GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools

Problem, Formatting or Query -  Send Feedback

Was this page helpful?-10+1


rfc:rfc909
                       Loader Debugger Protocol
                                RFC-909
                          Christopher Welles
                    BBN Communications Corporation
                            Walter Milliken
                           BBN Laboratories
                               July 1984

Status of This Memo

 This RFC specifies a proposed protocol for the ARPA Internet
 community, and requests discussion and suggestions for
 improvements.  Distribution of this memo is unlimited.
                           Table of Contents
   1   Introduction.......................................... 1
   1.1   Purpose of This Document............................ 1
   1.2   Summary of Features................................. 2
   2   General Description................................... 3
   2.1   Motivation.......................................... 3
   2.2   Relation to Other Protocols......................... 4
   2.2.1   Transport Service Requirements.................... 5
   3   Protocol Operation.................................... 9
   3.1   Overview............................................ 9
   3.2   Session Management.................................. 9
   3.3   Command Sequencing................................. 10
   3.4   Data Packing and Transmission...................... 10
   3.5   Implementations.................................... 12
   4   Commands and Formats................................. 15
   4.1   Packet Format...................................... 15
   4.2   Command Format..................................... 16
   4.2.1   Command Header................................... 16
   4.3   Addressing......................................... 19
   4.3.1   Long Address Format.............................. 20
   4.3.2   Short Address Format............................. 25
   5   Protocol Commands.................................... 29
   5.1   HELLO Command...................................... 29
   5.2   HELLO_REPLY........................................ 29
   5.3   SYNCH Command...................................... 33
   5.4   SYNCH_REPLY........................................ 34
   5.5   ABORT Command...................................... 35
   5.6   ABORT_DONE Reply................................... 35
   5.7   ERROR Reply........................................ 36
   5.8   ERRACK Acknowledgement............................. 39
   6   Data Transfer Commands............................... 41
   6.1   WRITE Command...................................... 42
   6.2   READ Command....................................... 43
   6.3   READ_DATA Response................................. 45
   6.4   READ_DONE Reply.................................... 47
   6.5   MOVE Command....................................... 48
   6.6   MOVE_DATA Response................................. 50
                                                              Page i
   6.7   MOVE_DONE Reply.................................... 52
   6.8   REPEAT_DATA........................................ 53
   6.9   WRITE_MASK Command (Optional)...................... 54
   7   Control Commands..................................... 59
   7.1   START Command...................................... 59
   7.2   STOP Command....................................... 61
   7.3   CONTINUE Command................................... 62
   7.4   STEP Command....................................... 62
   7.5   REPORT Command..................................... 63
   7.6   STATUS Reply....................................... 64
   7.7   EXCEPTION Trap..................................... 66
   8   Management Commands.................................. 69
   8.1   CREATE Command..................................... 69
   8.2   CREATE_DONE Reply.................................. 74
   8.3   DELETE Command..................................... 75
   8.4   DELETE_DONE Reply.................................. 76
   8.5   LIST_ADDRESSES Command............................. 76
   8.6   ADDRESS_LIST Reply................................. 77
   8.7   LIST_BREAKPOINTS Command........................... 79
   8.8   BREAKPOINT_LIST Reply.............................. 80
   8.9   LIST_PROCESSES Command............................. 82
   8.10   PROCESS_LIST Reply................................ 83
   8.11   LIST_NAMES Command................................ 84
   8.12   NAME_LIST Reply................................... 85
   8.13   GET_PHYS_ADDR Command............................. 87
   8.14   GOT_PHYS_ADDR Reply............................... 88
   8.15   GET_OBJECT Command................................ 90
   8.16   GOT_OBJECT Reply.................................. 91
   9   Breakpoints and Watchpoints.......................... 93
   9.1   BREAKPOINT_DATA Command............................ 95
   10   Conditional Commands................................ 99
   10.1   Condition Command Format......................... 100
   10.2   COUNT Conditions................................. 101
   10.3   CHANGED Condition................................ 102
   10.4   COMPARE Condition................................ 103
   10.5   TEST Condition................................... 105
   11   Breakpoint Commands................................ 109
   11.1   INCREMENT Command................................ 109
   11.2   INC_COUNT Command................................ 110
   11.3   OR Command....................................... 111
   11.4   SET_PTR Command.................................. 112
   11.5   SET_STATE Command................................ 113
   Page ii
   A   Diagram Conventions................................. 115
   B   Command Summary..................................... 117
   C   Commands, Responses and Replies..................... 121
   D   Glossary............................................ 123
                                                            Page iii
                                FIGURES
   1  Relation to Other Protocols............................ 4
   2  Form of Data Exchange Between Layers................... 6
   3  Packing of 16-bit Words............................... 11
   4  Packing of 20-bit Words............................... 12
   5  Network Packet Format................................. 15
   6  LDP Command Header Format............................. 16
   7  Command Classes....................................... 17
   8  Command Types......................................... 18
   9  Long Address Format................................... 20
   10  Long Address Modes................................... 21
   11  Short Address Format................................. 26
   12  Short Address Modes.................................. 27
   13  HELLO Command Format................................. 29
   14  HELLO_REPLY Format................................... 30
   15  System Types......................................... 31
   16  Target Address Codes................................. 31
   17  Feature Levels....................................... 32
   18  Options.............................................. 33
   19  SYNCH Command Format................................. 33
   20  SYNCH_REPLY Format................................... 34
   21  ABORT Command Format................................. 35
   22  ABORT_DONE Reply Format.............................. 36
   23  ERROR Reply Format................................... 37
   24  ERROR Codes.......................................... 38
   25  ERRACK Command Format................................ 40
   26  WRITE Command Format................................. 42
   27  READ Command Format.................................. 44
   28  DATA Response Format................................. 46
   29  READ_DONE Reply Format............................... 47
   30  MOVE Command Format.................................. 49
   31  MOVE_DATA Response Format............................ 51
   32  MOVE_DONE Reply Format............................... 52
   33  REPEAT_DATA Command Format........................... 54
   34  WRITE_MASK Format.................................... 56
   35  START Command Format................................. 60
   36  STOP Command Format.................................. 61
   37  CONTINUE Command Format.............................. 62
   38  STEP Command Format.................................. 63
   39  REPORT Command Format................................ 64
   40  STATUS Reply Format.................................. 65
   41  EXCEPTION Format..................................... 66
   42  CREATE Command Format................................ 70
   Page iv
   43  Create Types......................................... 71
   44  CREATE BREAKPOINT Format............................. 71
   45  CREATE MEMORY_OBJECT Format.......................... 73
   46  CREATE_DONE Reply Format............................. 74
   47  DELETE Command Format................................ 75
   48  DELETE_DONE Reply Format............................. 76
   49  LIST_ADDRESSES Command Format........................ 77
   50  ADDRESS_LIST Reply Format............................ 78
   51  LIST_BREAKPOINTS Command Format...................... 80
   52  BREAKPOINT_LIST Reply Format......................... 81
   53  LIST_PROCESSES Command Format........................ 82
   54  PROCESS_LIST Reply Format............................ 84
   55  LIST_NAMES Command Format............................ 85
   56  NAME_LIST Reply Format............................... 86
   57  GET_PHYS_ADDR Command Format......................... 88
   58  GOT_PHYS_ADDR Reply Format........................... 89
   59  GET_OBJECT Command Format............................ 90
   60  GOT_OBJECT Reply Format.............................. 91
   61  Commands to Manipulate Breakpoints................... 93
   62  Breakpoint Conditional Command Lists................. 95
   63  BREAKPOINT_DATA Command Format....................... 96
   64  Breakpoint Data Stream Format........................ 97
   65  Conditional Command Summary.......................... 99
   66  Condition Command Header............................ 101
   67  COUNT Condition Format.............................. 101
   68  CHANGED Condition................................... 102
   69  COMPARE Condition................................... 104
   70  TEST Condition...................................... 106
   71  Breakpoint Command Summary.......................... 109
   72  INCREMENT Command Format............................ 110
   73  INC_COUNT Command Format............................ 111
   74  OR Command Format................................... 111
   75  SET_PTR Command Format.............................. 112
   76  SET_STATE Command Format............................ 113
   77  Sample Diagram...................................... 115
   78  Command Summary..................................... 118
   79  Commands, Responses and Replies..................... 122
                                                              Page v
                               CHAPTER 1
                             Introduction
        The Loader-Debugger Protocol (LDP) is an  application  layer
   protocol   for  loading, dumping  and  debugging  target machines
   from hosts in a network environment.  This protocol  is  designed
   to  accommodate a variety  of  target  cpu  types.  It provides a
   powerful set of debugging services.  At  the  same  time,  it  is
   structured  so  that  a  simple  subset  may  be  implemented  in
   applications like boot  loading   where efficiency and space  are
   at a premium.
        The authors would like  to  thank  Dan  Franklin  and  Peter
   Cudhea  for providing many of the ideas on which this protocol is
   based.
   1.1  Purpose of This Document
        This is a technical specification for the LDP protocol.   It
   is intended to be comprehensive enough to be used by implementors
   of the  protocol.   It  contains  detailed  descriptions  of  the
   formats  and usage of over forty commands.  Readers interested in
   an overview of LDP should read the Summary  of  Features,  below,
   and  skim  Sections  2  through  3.1.   Also  see Appendix B, the
   Command Summary.  The remainder of the document reads  best  when
   accompanied by strong coffee or tea.
                                                              Page 1
   RFC-909                                                 July 1984
   1.2  Summary of Features
        LDP has the following features:
        o   commands to perform loading, dumping and debugging
        o   support for multiple connections to a single target
        o   reliable performance in an internet environment
        o   a small protocol subset for target loaders
        o   addressing  modes  and  commands  to  support   multiple
            machine types
        o   breakpoints and watchpoints  which  run  in  the  target
            machine.
   Page 2
   LDP Specification                             General Description
                               CHAPTER 2
                          General Description
   2.1  Motivation
        LDP is an  application  protocol  that  provides  a  set  of
   commands  used  by  application programs for loading, dumping and
   debugging target machines across a network.
        The goals of this protocol are shown in the following list:
        o   The protocol should support various processor types  and
            operating  systems.   Overhead  and complexity should be
            minimized for simpler cases.
        o   The protocol should provide support for applications  in
            which  more  than  one  user  can  debug the same target
            machine.  This implies an underlying transport mechanism
            that supports multiple connections between a host-target
            pair.
        o   LDP should have a minimal subset of  commands  for  boot
            loading  and dumping.  Target machine implementations of
            these applications are often restricted in the amount of
            code-space  they  may  take.   The  services  needed for
            loading and dumping  should  be  provided  in  a  small,
            easily implemented set of commands.
        o   There should be a means for communicating exceptions and
            errors from the target LDP process to the host process.
        o   LDP should allow the application to implement a full set
            of debugging functions without crippling the performance
            of the target's application (i.e., PSN,  PAD,  gateway).
            For  example,  a  breakpoint  mechanism  that  halts the
            target machine while breakpoint commands are  sent  from
            the  host  to the target is of limited usefulness, since
            the target will  be  unable  to  service  the  real-time
                                                              Page 3
   RFC-909                                                 July 1984
            demands of its application.
   2.2  Relation to Other Protocols
        LDP is an application protocol that fits  into  the  layered
   internet  protocol environment. Figure 1 illustrates the place of
   LDP in the protocol hierarchy.
                +------------------------------+
                |              LDP             |        Application
                +------------------------------+        Layer
                      |                  |
                      |                  |
                      |                  |
                +---------+          +---------+
                |   RDP   |    or    |  TCP    |        Transport Layer
                +---------+          +---------+
                  | or |                |
                  |    |                |
                  |  +--------------------+
                  |  |  Internet Protocol |             Internetwork
                  |  +--------------------+             Layer
                  |              |
                +------------------------------+
                |    Network Access Protocol   |        Network Layer
                +------------------------------+
                      Relation to Other Protocols
                               Figure 1
   Page 4
   LDP Specification                             General Description
   2.2.1  Transport Service Requirements
        LDP requires that the underlying transport layer:
        o   allow connections to be opened by specifying  a  network
            (or  internet)  address.   Support  passive  and  active
            opens.
        o   for each connection, specify the maximum message size.
        o   provide a mechanism for sending and  receiving  messages
            over an open connection.
        o   deliver messages reliably and in sequence
        o   support multiple connections, and  distinguish  messages
            associated  with  different connections.  This is only a
            requirement where LDP is  expected  to  support  several
            users at the same time.
        o   explictly return the outcome (success/failure)  of  each
            request  (open,  send,  receive), and provide a means of
            querying the  status  of  a  connection  (unacknowledged
            message count, etc.).
        Data is passed from the application program to the LDP  user
   process  in  the  form of commands.  In the case of an LDP server
   process, command responses originate in LDP itself.  Below LDP is
   the  transport  protocol.  The  Reliable  Data  Protocol  (RDP --
   RFC 908) is the recommended transport procotol.  Data  is  passed
   across  the  LDP/RDP interface in the form of messages.  (TCP may
   be used in place of RDP, but it will be  less  efficient  and  it
   will  require  more  resources  to implement.)  An internet layer
   (IP) normally comes between RDP and the network  layer,  but  RDP
   may exchange data packets directly with the network layer.
        Figure  2  shows  the  flow  of  data  across  the  protocol
   interfaces:
                                                              Page 5
   RFC-909                                                 July 1984
                             +------+
                             |      |
                             |Appli-|
                             |cation|
                             |      |
                             +------+
                                ^
                     Commands   |
                                V
                             +------+
                             |      |
                             | LDP  |
                             |      |
                             +------+
                                ^
                     Messages   |
                                V
                             +-----+
                             |     |
                             | RDP |
                             |     |
                             +-----+
                                ^
                     Segments   |
                                V
                              +----+
                              |    |
                              | IP |
                              |    |
                              +----+
                                ^
                     Datagrams  |
                                V
                            ?  *     !
                         $  =      ^   +
                           *
                        >    Internet
                          ,            ?
                               !    )
                            *   %     $
                 Form of Data Exchange Between Layers
                               Figure 2
   Page 6
   LDP Specification                             General Description
                                                              Page 7
   RFC-909                                                 July 1984
   Page 8
   LDP Specification                              Protocol Operation
                               CHAPTER 3
                          Protocol Operation
   3.1  Overview
        An LDP session consists  of  an  exchange  of  commands  and
   responses  between an LDP user process and an LDP server process.
   Normally,  the  user  process  resides  on  a  host  machine   (a
   timesharing  computer  used  for network monitoring and control),
   and the server process resides on a  target  machine  (PSN,  PAD,
   gateway,  etc.).   Throughout  this document, host and target are
   used  as  synonyms  for  user   process   and   server   process,
   respectively,  although  in  some implementations (the Butterfly,
   for example) this  correspondence  may  be  reversed.   The  host
   controls  the  session  by  sending commands to the target.  Some
   commands elicit responses, and all commands may elicit  an  error
   reply.
        The protocol contains five classes  of  commands:  protocol,
   data  transfer,  management,   control  and breakpoint.  Protocol
   commands are used to verify the command sequencing mechanism  and
   to handle erroneous commands.  Data transfer commands involve the
   transfer of data from one place to another, such  as  for  memory
   examine/deposit,  or  loading.  Management  commands are used for
   creating   and   deleting   objects   (processes,    breakpoints,
   watchpoints,  etc.)  in the target machine.  Control commands are
   used to control the execution of  target  code  and  breakpoints.
   Breakpoint commands are used to control the execution of commands
   inside breakpoints and watchpoints.
   3.2  Session Management
        An LDP session consists of a series of commands sent from  a
   host  LDP  to  a  target  LDP,  some  of which may be followed by
   responses from the target.  A session begins when a host opens  a
   transport  connection to a target listening on a well known port.
   LDP uses RDP port number zzz or TCP port number  yyy.   When  the
   connection  has been established, the host sends a HELLO command,
   and the target  replies  with  a  HELLO_REPLY.   The  HELLO_REPLY
   contains  parameters that describe the target's implementation of
   LDP, including protocol  version,  implementation  level,  system
                                                              Page 9
   RFC-909                                                 July 1984
   type,  and  address format.  The session terminates when the host
   closes the underlying  transport  connection.   When  the  target
   detects  that the transport connection has been closed, it should
   deallocate any resources dedicated to the session.
        The target process is the passive partner in an LDP session,
   and  it  waits for the host process to terminate the session.  As
   an implementation consideration, either LDP  or  the   underlying
   transport  protocol  in  the  target  should  have  a  method for
   detecting if the host process  has  died.   Otherwise,   an   LDP
   target  that  supported  only  one  connection  could be rendered
   useless by a host that crashed in the  middle of a session.   The
   problem  of  detecting  half-dead  connections  can be avoided by
   taking a different tack:  the target could allow new  connections
   to  usurp  inactive  connections.  A  connection with no activity
   could be declared 'dead', but would  not  be  usurped  until  the
   connection  resource  was  needed.   However,  this  would  still
   require the transport layer to support two  connection  channels:
   one  to  receive  connection  requests, and another to use for an
   active connection.
   3.3  Command Sequencing
        Each command sent from the host to the target has a sequence
   number.   The  sequence  number is used by the target to refer to
   the command in normal replies and error replies.  To save  space,
   these  numbers  are  not  actually  included  in  host  commands.
   Instead, each command sent from the host is assigned an  implicit
   sequence  number.   The  sequence  number  starts  at zero at the
   beginning of the LDP  session  and  increases  by  one  for  each
   command sent.  The host and target each keep track of the current
   number.  The SYNCH <sequence number> command may be used  by  the
   host to synchronize the sequence number.
   3.4  Data Packing and Transmission
        The convention for the order of data packing was chosen  for
   its  simplicity:  data  are packed most significant bit first, in
   order of increasing target address, into  eight-bit  octets.  The
   octets of packed data are transmitted in sequential order.
   Page 10
   LDP Specification                              Protocol Operation
        Data are always packed according to the  address  format  of
   the  target  machine.   For  example, in an LDP session between a
   20-bit host and  a  16-bit  target,  16-bit  words  (packed  into
   octets)   are  transmitted  in  both  directions.   For  ease  of
   discussion, targets are treated here  as  if  they  have  uniform
   address  spaces.  In practice, the size of address units may vary
   within a target -- 16-bit macromemory, 32-bit micromemory, 10-bit
   dispatch  memory,  etc.   Data packing between host and target is
   tailored to the units of the current target address space.
        Figures showing the packing of data for targets with various
   address  unit  sizes  are given below.  The order of transmission
   with respect to the diagrams is top to bottom.  Bit numbering  in
   the  following diagrams refers to significance in the octet:  bit
   zero  is  the  least  significant  bit  in  an  octet.   For   an
   explanation  of  the bit numbering convention that applies in the
   rest of this document, please see Appendix A.
        The packing of data for targets with word lengths  that  are
   multiples   of  8  is  straightforward.   The  following  diagram
   illustrates 16-bit packing:
                        7                               0
                        ---------------------------------
             Octet 0    |      WORD 0 bits 15-08        |
                        ---------------------------------
             Octet 1    |      WORD 0 bits 07-00        |
                        ---------------------------------
             Octet 2    |      WORD 1 bits 15-08        |
                        ---------------------------------
             Octet 3    |      WORD 1 bits 07-00        |
                        ---------------------------------
                                      *
                                      *
                                      *
                        ---------------------------------
             Octet 2n-1 |      WORD n bits 07-00        |
                        ---------------------------------
                        Packing of 16-bit Words
                               Figure 3
                                                             Page 11
   RFC-909                                                 July 1984
   Packing  for  targets  with  peculiar  word   lengths   is   more
   complicated.   For  20-bit  machines,  2 words of data are packed
   into  5  octets.   When  an  odd  number  of  20-bit  words   are
   transmitted,  the  partially used octet is included in the length
   of the command, and the octet is padded to the right with zeroes.
                        7                               0
                        ---------------------------------
             Octet 0    |      WORD 0 bits 19-12        |
                        ---------------------------------
             Octet 1    |      WORD 0 bits 11-04        |
                        ---------------------------------
             Octet 2    |  WORD 0 03-00 |  WORD 1 19-16 |
                        ---------------------------------
             Octet 3    |      WORD 1 bits 15-08        |
                        ---------------------------------
             Octet 4    |      WORD 1 bits 07-00        |
                        ---------------------------------
                        Packing of 20-bit Words
                               Figure 4
   3.5  Implementations
        A subset of LDP commands may be implemented in targets where
   machine  resources  are  limited and the full capabilities of LDP
   are  not  needed.  There  are  three  basic  levels   of   target
   implementations:       LOADER_DUMPER,      BASIC_DEBUGGER     and
   FULL_DEBUGGER.  The target communicates  its  LDP  implementation
   level  to the host during session initiation.  The implementation
   levels are described below:
   Page 12
   LDP Specification                              Protocol Operation
   LOADER_DUMPER
        Used  for   loading/dumping    of   the   target    machine.
        Includes   all  protocol   class  commands and replies; data
        transfer commands READ, WRITE,  MOVE  and  their  responses;
        control   command   START  and  control  reply    EXCEPTION.
        Understands at least PHYS_MACRO and HOST  addressing  modes;
        others if desired.
   BASIC_DEBUGGER
        Implements  LOADER_DUMPER  commands,  all  control commands,
        all  addressing modes appropriate to the target machine, but
        does  not  have finite state machine  (FSM)  breakpoints  or
        watchpoints.   Default  breakpoints  are  implemented.   The
        target understands long addressing mode.
   FULL_DEBUGGER
        Implements all commands and addressing modes appropriate  to
        the   target  machine,  and  includes  breakpoint  commands,
        conditional commands and BREAKPOINT_DATA.   Watchpoints  are
        optional.
                                                             Page 13
   RFC-909                                                 July 1984
   Page 14
   LDP Specification                            Commands and Formats
                               CHAPTER 4
                         Commands and Formats
   4.1  Packet Format
        LDP commands are enclosed in RDP transport messages.  An RDP
   message  may contain more than one command, but each command must
   fit entirely within a single message.  Network packets containing
   LDP commands have the format shown in Figure 5.
                    +----------------+
                    |  Local Network |
                    |    Header(s)   |
                    +----------------+
                    |   IP Header    |
                    +----------------+
                    |   RDP Header   |
                    +----------------+     +-+
                    |   LDP Command  |      |
                    |   Header       |      |
                    +----------------+      |
                    |   Optional     |      |
                    .   LDP          .      | LDP Command
                    .   Data         .      | Format
                    |                |      |
                    +----------------+      |
                    |   LDP Padding  |      |
                    +----------------+     +-+
                    |   Additional   |
                    .   LDP          .
                    .   Commands     .
                    .                .
                    +----------------+
                         Network Packet Format
                               Figure 5
                                                             Page 15
   RFC-909                                                 July 1984
   4.2  Command Format
        LDP commands consist of a standard two-word header  followed
   optionally  by  additional data.  To facilitate parsing of multi-
   command messages, all commands contain an even number of  octets.
   Commands that contain an odd number of data octets must be padded
   with a null octet.
        The commands defined by the LDP specification  are  intended
   to  be of universal application to provide a common basis for all
   implementations.  Command class and type codes from 0 to 63.  are
   reserved  by the protocol.  Codes above 63. are available for the
   implementation of target-specific commands.
   4.2.1  Command Header
        LDP commands begin with a fixed length header.   The  header
   specifies the type of command and its length in octets.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |     Command Length (octets)   |
                    +---------------+---------------+
                  1 | Command Class | Command Type  |
                    +---------------+---------------+
                       LDP Command Header Format
                               Figure 6
   HEADER FIELDS:
   Command Length
        The command length gives the total number of octets  in  the
        command,  including the length field and data, and excluding
        padding.
   Command Class
   Command Type
   Page 16
   LDP Specification                            Commands and Formats
        The command class and type  together  specify  a  particular
        command.   The  class selects one of six command categories,
        and the type gives the command within  that  category.   All
        codes are decimal.  The symbols given in Figures 7 and 8 for
        command classes and types are used in the remainder of  this
        document for reference.
        The command classes that have been defined are:
                   Command Class  |  Symbol
                  ----------------+-----------
                          1       | PROTOCOL
                          2       | DATA_TRANSFER
                          3       | CONTROL
                          4       | MANAGEMENT
                          5       | BREAKPOINT
                          6       | CONDITION
                          7 - 63  | <reserved>
                            Command Classes
                               Figure 7
        Command  type  codes  are  assigned  in  order  of  expected
        frequency  of use.  Commands and their responses/replies are
        numbered  sequentially.   The  command  types,  ordered   by
        command class, are:
                                                             Page 17
   RFC-909                                                 July 1984
                   Command Class  |  Command Type | Symbol
                  ----------------+---------------+----------
                    PROTOCOL      |       1       | HELLO
                                  |       2       | HELLO_REPLY
                                  |       3       | SYNCH
                                  |       4       | SYNCH_REPLY
                                  |       5       | ERROR
                                  |       6       | ERRACK
                                  |       7       | ABORT
                                  |       8       | ABORT_DONE
                                  |       9 - 63  | <reserved>
                                  |               |
                    DATA_TRANSFER |       1       | WRITE
                                  |       2       | READ
                                  |       3       | READ_DONE
                                  |       4       | READ_DATA
                                  |       5       | MOVE
                                  |       6       | MOVE_DONE
                                  |       7       | MOVE_DATA
                                  |       8       | REPEAT_DATA
                                  |       9       | BREAKPOINT_DATA
                                  |       10      | WRITE_MASK
                                  |       11 - 63 | <reserved>
                                  |               |
                    CONTROL       |       1       | START
                                  |       2       | STOP
                                  |       3       | CONTINUE
                                  |       4       | STEP
                                  |       5       | REPORT
                                  |       6       | STATUS
                                  |       7       | EXCEPTION
                                  |       8 - 63  | <reserved>
                                  |               |
                    MANAGEMENT    |       1       | CREATE
                                  |       2       | CREATE_DONE
                                  |       3       | DELETE
                                  |       4       | DELETE_DONE
                                  |       5       | LIST_ADDRESSES
                                  |       6       | ADDRESS_LIST
                                  |       7       | GET_PHYS_ADDRESS
                                  |       8       | GOT_PHYS_ADDRESS
                                  |       9       | GET_OBJECT
                                  |       10      | GOT_OBJECT
                                  |       11      | LIST_BREAKPOINTS
                                  |       12      | BREAKPOINT_LIST
   Page 18
   LDP Specification                            Commands and Formats
                                  |       13      | LIST_NAMES
                                  |       14      | NAME_LIST
                                  |       15      | LIST_PROCESSES
                                  |       16      | PROCESS_LIST
                                  |       17 - 63 | <reserved>
                                  |               |
                    BREAKPOINT    |       1       | INCREMENT
                                  |       2       | INC_COUNT
                                  |       3       | OR
                                  |       4       | SET_PTR
                                  |       5       | SET_STATE
                                  |       6 - 63  | <reserved>
                                  |               |
                    CONDITION     |       1       | CHANGED
                                  |       2       | COMPARE
                                  |       3       | COUNT_EQ
                                  |       4       | COUNT_GT
                                  |       5       | COUNT_LT
                                  |       6       | TEST
                                  |       7 - 63  | <reserved>
                             Command Types
                               Figure 8
   4.3  Addressing
        Addresses are used  in  LDP  commands  to  refer  to  memory
   locations,  processes,  buffers,  breakpoints and other entities.
   Many of these entities are machine-dependent; some machines  have
   named  objects,  some  machines have multiple address spaces, the
   size of address spaces varies, etc.  The  format  for  specifying
   addresses  needs  to  be  general  enough  to handle all of these
   cases.   This  speaks  for  a  large,  hierarchically  structured
   address  format.   However, the disadvantage of a large format is
   that it imposes extra overhead on communication with targets that
   have simpler address schemes.
        LDP resolves this conflict by employing two address formats:
   a  short  three-word format for addressing simpler targets, and a
   long five-word format for others.  Each target LDP is required to
   implement  at least one of these formats.  At the start of an LDP
   session, the target specifies the address format(s)  it  uses  in
                                                             Page 19
   RFC-909                                                 July 1984
   the  Flag field of the HELLO_REPLY message.  In each address, the
   first bit of the mode octet is a format flag:  0  indicates  LONG
   address format, and 1 indicates SHORT format.
   4.3.1  Long Address Format
        The long address format is five words long and consists of a
   three-word  address  descriptor and a two-word offset (see Figure
   9). The descriptor specifies an address space to which the offset
   is applied.  The descriptor is subdivided into several fields, as
   described below.  The structuring of the descriptor  is  designed
   to  support  complex  addressing  modes.  For example, on targets
   with  multiple  processes,  descriptors  may  reference   virtual
   addresses,  registers,  and  other  entities  within a particular
   process.
        The addressing modes defined below are intended as a base to
   which  target-specific  modes  may be added.  Modes up to 63. are
   reserved by the protocol.  The range 64. to 127. may be used  for
   target-specific address modes.
             Long Format - Format bit is LONG=0
              0             0 0   1         1
              0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
             +-------------------------------+  +-+
             |0|       Mode  |  Mode Arg     |   |
             +-------------------------------+   |
             |                    (31-16)    |   | Descriptor
             +----          ID            ---+   |
             |                    (15-0)     |   |
             +-------------------------------+  +-+
             |                    (31-16)    |   |
             +----        Offset          ---+   | Offset
             |                    (15-0)     |   |
             +-------------------------------+  +-+
                          Long Address Format
                               Figure 9
   LONG ADDRESS FIELDS:
   Page 20
   LDP Specification                            Commands and Formats
   Mode
        The address mode identifies the type of address space  being
        referenced.   The mode is qualified by the mode argument and
        the ID field.  Implementation of modes other  than  physical
        and  host is machine-dependent.  Currently defined modes and
        the address space they reference are shown in Figure 10.
        Mode | Symbol               | Address space
        -----+----------------------+---------------------------
          0    HOST                   Host
          1    PHYS_MACRO             Macromemory
          2    PHYS_MICRO             Micromemory
          3    PHYS_I/O               I/O space
          4    PHYS_MACRO_PTR         Macro contains a pointer
          5    PHYS_REG               Register
          6    PHYS_REG_OFFSET        Register plus offset
          7    PHYS_REG_INDIRECT      Register contains address
                                      of a pointer
          8    PROCESS_CODE           Process code space
          9    PROCESS_DATA           Process data space
         10    PROCESS_DATA_PTR       Process data contains a ptr
         11    PROCESS_REG            Process virtual register
         12    PROCESS_REG_OFFSET     Process register plus offset
         13    PROCESS_REG_INDIRECT   Process register contains
                                      address of a pointer
         14    OBJECT_OFFSET          Memory object (queue, pool)
         15    OBJECT_HEADER          System header for an object
         16    BREAKPOINT             Breakpoint
         17    WATCHPOINT             Watchpoint
         18    BPT_PTR_OFFSET         Breakpoint ptr plus offset
         19    BPT_PTR_INDIRECT       Breakpoint ptr plus offset
                                      gives address of a pointer
         20 -  <reserved>
         63
                          Long Address Modes
                               Figure 10
   Mode Argument
                                                             Page 21
   RFC-909                                                 July 1984
        Provides a numeric argument to the  mode  field.   Specifies
        the  register  in  physical  and  process REG and REG_OFFSET
        modes.
   ID Field
        Identifies a particular process, buffer or object.
   Offset
        The offset into the linear  address  space  defined  by  the
        mode.  The size of the machine word determines the number of
        significant bits in the offset.   Likewise,  the  addressing
        units of the target are the units of the offset.
   The interpretation of the mode argument, ID field and offset  for
   each address mode is given below:
   HOST
        The ID and offset fields are numbers assigned arbitrarily by
        the  host  side  of the debugger.  These numbers are used in
        MOVE and MOVE_DATA messages.  MOVE_DATA responses containing
        this  mode  as the destination are sent by the target to the
        host.  This may occur in debugging when data is sent to  the
        host from the target breakpoint.
   PHYS_MACRO
        The  offset  contains  the  32-bit  physical  address  of  a
        location in macromemory.  The mode argument and ID field are
        not used.   For  example,  mode=PHYS_MACRO  and  offset=1000
        specifies location 1000 in physical memory.
   PHYS_MICRO
        Like PHYS_MACRO, but the location is in micromemory.
   PHYS_I/O
        Like PHYS_MACRO, but the location is in I/O space.
   PHYS_MACRO_PTR
        The offset contains the address of a pointer in macromemory.
        The  location  pointed to (the effective address) is also in
        macromemory.  The mode argument and ID field are unused.
   Page 22
   LDP Specification                            Commands and Formats
   PHYS_REG
        The mode argument  gives  the  physical  register.   If  the
        register  is  used by the LDP target process, then the saved
        copy from  the  previous  context  is  used.   This  comment
        applies  to  PHYS_REG_OFFSET  mode as well.  The ID field is
        not used.
   PHYS_REG_OFFSET
        The offset is added to the contents of a register  given  as
        the mode argument.  The result is used as a physical address
        in macromemory.  ID is unused.
   PHYS_REG_INDIRECT
        The register specified in the mode arg contains the  address
        of  a  pointer in macromemory.  The effective address is the
        macromemory location specified  in  the  pointer,  plus  the
        offset.  The ID field is unused.
   PROCESS_CODE
        The ID is a process ID, the offset is into  the  code  space
        for this process.  Mode argument is not used.
   PROCESS_DATA
        The ID is a process ID, the offset is into  the  data  space
        for  this  process.   Mode argument is not used.  On systems
        that do not distinguish between code and data  space,  these
        two  modes are equivalent, and reference the virtual address
        space of the process.
   PROCESS_DATA_PTR
        The offset contains the address of a  pointer  in  the  data
        space  of  the  process  specified  by the ID.  The location
        pointed to (the effective  address)  is  also  in  the  data
        space.  The mode argument is not used.
   PROCESS_REG
        Accesses the  registers  (and  other  system  data)  of  the
        process  given  by the ID field.  Mode argument 0 starts the
        registers.  After the registers, the  mode  argument  is  an
        offset into the system area for the process.
                                                             Page 23
   RFC-909                                                 July 1984
   PROCESS_REG_OFFSET
        The offset plus the contents of the register  given  in  the
        mode  argument specifies a location in the data space of the
        process specified by the ID.
   PROCESS_REG_INDIRECT
        The register specified in the mode arg contains the  address
        of  a  pointer in the data space of the process given by the
        ID.  The effective address is the location in  process  data
        space specified in the pointer, plus the offset.
   OBJECT_OFFSET (optional)
        The offset is into the memory space defined by the object ID
        in   ID.    Recommended  for  remote  control  of  parameter
        segments.
   OBJECT_HEADER (optional)
        The  offset  is  into  the  system  header  for  the  object
        specified by the ID.  Intended for use with the Butterfly.
   BREAKPOINT
        The descriptor specifies a breakpoint.  The offset is  never
        used,  this  type  is  only used in descriptors referring to
        breakpoints.  (See Breakpoints and Watchpoints,  below,  for
        an explanation of breakpoint descriptors.)
   WATCHPOINT
        The descriptor specifies a watchpoint.  The offset is  never
        used,  this  type  is  only used in descriptors referring to
        watchpoints.  (See Breakpoints and Watchpoints,  below,  for
        an explanation of watchpoint descriptors).
   BPT_PTR_OFFSET
        For  this  mode  and  BPT_PTR_INDIRECT,  the  mode  argument
        specifies  one  of two breakpoint pointer variables local to
        the breakpoint in which this address occurs.  These pointers
        and  the  SET_PTR command which manipulates them provide for
        an  arbitrary  amount  of  address  indirection.   They  are
        intended for use in traversing data structures: for example,
        chasing queues.  In BPT_PTR_OFFSET, the offset is  added  to
   Page 24
   LDP Specification                            Commands and Formats
        the  pointer  variable  to  give  the effective address.  In
        targets which support multiple processes, the location is in
        the  data  space of the process given by the ID.  Otherwise,
        the  location  is  a  physical  address   in   macro-memory.
        BPT_PTR.*   modes   are   valid   only  in  breakpoints  and
        watchpoints.
   BPT_PTR_INDIRECT
        Like BPT_PTR_OFFSET, except that it uses one more  level  of
        indirection.    The  pointer  variable  given  by  the  mode
        argument plus the offset specify an address which points  to
        the    effective    address.    See   the   description   of
        BPT_PTR_OFFSET for a discussion of  usage,  limitations  and
        address space.
   4.3.2  Short Address Format
        The  short  address  format   is   intended   for   use   in
   implementations  where protocol overhead must be minimized.  This
   format is a subset of the long address format:  it  contains  the
   same  fields  except  for  the  ID  field.   Therefore, the short
   addressing format supports only HOST and  PHYS_*  address  modes.
   Only  the LOADER_DUMPER implementation level commands may be used
   with the short addressing format.  The short  address  format  is
   three  words  long,  consisting  of  a 16-bit word describing the
   address space, and a 32-bit offset.
                                                             Page 25
   RFC-909                                                 July 1984
                  Short Format - Format bit is SHORT=1
                   0             0 0   1         1
                   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                  +-------------------------------+
                  |1|       Mode  | Mode Argument |
                  +-------------------------------+  +-+
                  |                    (31-16)    |   |
                  +----        Offset          ---+   | Offset
                  |                    (15-0)     |   |
                  +-------------------------------+  +-+
                         Short Address Format
                               Figure 11
   SHORT ADDRESS FIELDS:
   Mode
        The high-order  bit  is  1,  indicating  the  short  address
        format.   A  list  of  the  address modes supported is given
        below.  The interpretation of the  remaining  fields  is  as
        described above for the long addressing format.
   Page 26
   LDP Specification                            Commands and Formats
        Mode | Symbol             | Address space
        -----+--------------------+---------------------------
          0    HOST                 Host
          1    PHYS_MACRO           Macro-memory
          2    PHYS_MICRO           Micro-memory
          3    PHYS_I/O             I/O space
          4    PHYS_MACRO_PTR       Macro contains a pointer
          5    PHYS_REG             Register
          6    PHYS_REG_OFFSET      Register plus offset
          7    PHYS_REG_INDIRECT    Register contains address
                                    of a pointer
          8 -
          32   <reserved>
                          Short Address Modes
                               Figure 12
                                                             Page 27
   RFC-909                                                 July 1984
   Page 28
   LDP Specification                               Protocol Commands
                               CHAPTER 5
                           Protocol Commands
        Protocol  commands  are  used  for   error   handling,   for
   synchronizing  the command sequence number, and for communicating
   protocol implementation parameters.  Every protocol command has a
   corresponding  reply.   All  protocol  commands are sent from the
   host  to  the  target,  with  replies  flowing  in  the  opposite
   direction.
   5.1  HELLO Command
        The HELLO command is sent by the host to signal the start of
   an LDP session.  The target responds with HELLO_REPLY.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               4               |
                    +---------------+---------------+
                  1 |   PROTOCOL    |    HELLO      |
                    +---------------+---------------+
                         HELLO Command Format
                               Figure 13
   5.2  HELLO_REPLY
        A HELLO_REPLY is sent by the target in response to the HELLO
   command  at  the  start of an LDP session.  This reply is used to
   inform the host about the  target's implementation of LDP.
                                                             Page 29
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               10              |
                    +---------------+---------------+
                  1 |    PROTOCOL   |   HELLO_REPLY |
                    +---------------+---------------+
                  2 |   LDP Version |  System Type  |
                    +---------------+---------------+
                  3 |   Options |W|S| Implementation|
                    +---------------+---------------+
                  4 | Address Code  |    Reserved   |
                    +---------------+---------------+
                          HELLO_REPLY Format
                               Figure 14
   HELLO_REPLY FIELDS:
   LDP Version
        The  target's  LDP  protocol  version.    If   the   current
        host  protocol  version  does not agree  with  the  target's
        protocol  version,  the  host may terminate the session,  or
        may  continue it, at the discretion of the implementor.  The
        current version number is 2.
   System Type
        The type of system running on the target.  This is used as a
        check  against what the host thinks the target is.  The host
        is expected to have a table  of  target  system  types  with
        information  about  target  address  spaces, target-specific
        commands and addressing modes, and so forth.
        Currently defined system types are shown in Figure 15.  This
        list  includes  some  systems normally thought of as 'hosts'
        (e.g. C70, VAX), for implementations where targets  actively
        initiate and direct a load of themselves.
   Page 30
   LDP Specification                               Protocol Commands
           Code |  System       |  Description
        --------+---------------+---------------------------
             1     C30_16_BIT      BBN 16-bit C30
             2     C30_20_BIT      BBN 20-bit C30
             3     H316            Honeywell-316
             4     BUTTERFLY       BBN Butterfly
             5     PDP-11          DEC PDP-11
             6     C10             BBN C10
             7     C50             BBN C50
             8     PLURIBUS        BBN Pluribus
             9     C70             BBN C70
            10     VAX             DEC VAX
            11     MACINTOSH       Apple MacIntosh
                             System Types
                               Figure 15
   Address Code
        The address code indicates which LDP address  format(s)  the
        target is prepared to use.  Address codes are show in Figure
        16.
         Address Code |  Symbol       | Description
        --------------+---------------+-----------------------------
              1         LONG_ADDRESS    Five word address format.
                                        Supports all address modes
                                        and commands.
              2         SHORT_ADDRESS   Three word address format.
                                        Supports only physical and
                                        host address modes.  Only
                                        the LOADER_DUMPER set of
                                        commands are supported.
                         Target Address Codes
                               Figure 16
   Implementation
                                                             Page 31
   RFC-909                                                 July 1984
        The implementation level   specifies   which   features   of
        the   protocol   are  implemented  in the target.  There are
        three levels of protocol implementation.  These  levels  are
        intended to correspond to the three most likely applications
        of LDP:  simple loading and dumping,  basic  debugging,  and
        full  debugging.   (Please see Implementations, above, for a
        detailed description of implementation  levels.)  There  are
        are  also several optional features that are not included in
        any particular level.
        Implementation levels are cumulative, that is,  each  higher
        level  includes  the  features  of all previous levels.  The
        levels are shown in Figure 17.
        Feature Level |  Symbol       | Description
        --------------+---------------+-----------------------------
               1        LOADER_DUMPER   Loader/dumper subset of LDP
               2        BASIC_DEBUGGER  Control commands, CREATE
               3        FULL_DEBUGGER   FSM breakpoints
                            Feature Levels
                               Figure 17
   Options
        The options field (see  Figure  18)  is  an  eight-bit  flag
        field.   Bit  flags  are  used to indicate if the target has
        implemented particular optional commands.  Not all  optional
        commands  are  referenced  in  this  field.  Commands  whose
        implementation   depends  on  target  machine  features  are
        omitted.   The  LDP  application is expected to 'know' about
        target features that are  not  intrinsic  to  the  protocol.
        Examples  of  target-dependent  commands  are  commands that
        refer to named objects (CREATE, LIST_NAMES).
   Page 32
   LDP Specification                               Protocol Commands
              Mask |  Symbol     | Description
             ------+-------------+---------------+-----------------
               1     STEP          The STEP command is implemented
               2     WATCHPOINTS   Watchpoints are implemented
                                Options
                               Figure 18
   5.3  SYNCH Command
        The SYNCH command is sent by the host  to  the  target.  The
   target  responds  with  a  SYNCH_REPLY.   The SYNCH - SYNCH_REPLY
   exchange serves two functions: it synchronizes the host-to-target
   implicit sequence number and acts as a cumulative acknowledgement
   of the receipt and execution of  all  host  commands  up  to  the
   SYNCH.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               6               |
                    +---------------+---------------+
                  1 |   PROTOCOL    |    SYNCH      |
                    +---------------+---------------+
                  2 |       Sequence Number         |
                    +---------------+---------------+
                         SYNCH Command Format
                               Figure 19
   SYNCH FIELDS:
   Sequence Number
                                                             Page 33
   RFC-909                                                 July 1984
        The sequence number of this command.  If this  is  not  what
        the  target  is  expecting,  the target will reset to it and
        respond with an ERROR reply.
   5.4  SYNCH_REPLY
        A SYNCH_REPLY is sent by the target in reponse  to  a  valid
   SYNCH  command.   A SYNCH command is valid if its sequence number
   agrees  with  the  sequence  number  the  target  is   expecting.
   Otherwise, the target will reset its sequence number to the SYNCH
   command and send an ERROR reply.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               6               |
                    +---------------+---------------+
                  1 |   PROTOCOL    |  SYNCH_REPLY  |
                    +---------------+---------------+
                  2 |       Sequence Number         |
                    +---------------+---------------+
                          SYNCH_REPLY Format
                               Figure 20
   SYNCH_REPLY FIELDS:
   Sequence Number
        The sequence number of  the  SYNCH  command  to  which  this
        SYNCH_REPLY is the response.
   Page 34
   LDP Specification                               Protocol Commands
   5.5  ABORT Command
        The ABORT command is sent from the host to abort all pending
   operations  at  the target.  The target responds with ABORT_DONE.
   This is primarily intended to stop large data transfers from  the
   target.  A likely application would be during a debugging session
   when the user types an interrupt to abort  a  large  printout  of
   data  from  the  target.   The ABORT command has no effect on any
   breakpoints or watchpoints that may be enabled in the target.
        As a practical matter, the ABORT command may be difficult to
   implement  on  some  targets.   Its  ability to interrupt command
   processing on the target depends on the target being able to look
   ahead at incoming commands and receive an out-of-band signal from
   the host.  However, the effect of an ABORT  may  be  achieved  by
   simply closing and reopening the transport connection.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               4               |
                    +---------------+---------------+
                  1 |   PROTOCOL    |    ABORT      |
                    +---------------+---------------+
                         ABORT Command Format
                               Figure 21
   5.6  ABORT_DONE Reply
        The ABORT_DONE reply is sent from the target to the host  in
   response to an ABORT command.  This indicates that the target has
   terminated all  operations  that  were  pending  when  the  ABORT
   command  was  received.  The sequence number of the ABORT command
   is included in the reply.
                                                             Page 35
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               4               |
                    +---------------+---------------+
                  1 |   PROTOCOL    |    ABORT_DONE |
                    +---------------+---------------+
                  2 |       Sequence Number         |
                    +---------------+---------------+
                        ABORT_DONE Reply Format
                               Figure 22
   ABORT_DONE FIELDS:
   Sequence Number
        The sequence number of the ABORT command that elicited  this
        reply.   This  enables   the  host  to  distinguish  between
        replies to multiple aborts.
   5.7  ERROR Reply
        The ERROR reply is sent by the target in response to  a  bad
   command.   The  ERROR  reply  gives  the  sequence  number of the
   offending command and a reason code.  The target ignores  further
   commands   until  an  ERRACK command is received.  The reason for
   ignoring commands is that the  proper  operation  of  outstanding
   commands  may  be  predicated  on  the execution of the erroneous
   command.
   Page 36
   LDP Specification                               Protocol Commands
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 |   PROTOCOL    |    ERROR      |
                    +---------------+---------------+
                  2 |   Command Sequence Number     |
                    +---------------+---------------+
                  3 |          Error code           |
                    +---------------+---------------+
                  4 |       Optional Data           |
                    +---------------+---------------+
                                    *
                                    *
                                    *
                    +---------------+---------------+
                  n |       Optional Data           |
                    +---------------+---------------+
                          ERROR Reply Format
                               Figure 23
   ERROR Reply FIELDS:
   Command Sequence Number
        The implicit sequence number of the erroneous command.
   Error Code
        A code specifying what error has taken place.  The currently
        defined codes are shown in Figure 24.
                                                             Page 37
   RFC-909                                                 July 1984
                  Error Code |  Symbol
                  -----------+------------------------
                      1         BAD_COMMAND
                      2         BAD_ADDRESS_MODE
                      3         BAD_ADDRESS_ID
                      4         BAD_ADDRESS_OFFSET
                      5         BAD_CREATE_TYPE
                      6         NO_RESOURCES
                      7         NO_OBJECT
                      8         OUT_OF_SYNCH
                      9         IN_BREAKPOINT
                              ERROR Codes
                               Figure 24
        An explanation of each of these error codes follows:
        BAD_COMMAND
             The command was not meaningful to the  target  machine.
             This includes commands that are valid but unimplemented
             in this target.  Also, the command  was  not  valid  in
             this context.  For example, a command given by the host
             that  is  only  legal  in  a   breakpoint   (e.g.   IF,
             SET_STATE).
        BAD_ADDRESS_MODE <offending-address>
             The mode of an address given  in  the  command  is  not
             meaningful  to  this  target  system.   For  example, a
             PROCESS address mode on a target that does not  support
             multi-processing.
        BAD_ADDRESS_ID <offending-address>
             The ID field of an  address  didn't  correspond  to  an
             appropriate  thing.  For example, for a PROCESS address
             mode, the ID of a non-existent process.
        BAD_ADDRESS_OFFSET <offending-address>
             The offset field of the address was outside  the  legal
             range  for the thing addressed.  For example, an offset
             of 200,000 in PHYS_MACRO mode on a target with  64K  of
   Page 38
   LDP Specification                               Protocol Commands
             macro-memory.
        BAD_CREATE_TYPE
             The object type in a CREATE command was unknown.
        NO_RESOURCES
             A CREATE  command  failed  due  to  lack  of  necessary
             resources.
        NO_OBJECT
             A GET_OBJECT command failed to find the named object.
        OUT_OF_SYNCH
             The sequence  number  of  the  SYNCH  command  was  not
             expected  by the target.  The target has resynchronized
             to it.
        IN_BREAKPOINT <breakpoint-descriptor> <breakpoint-sequence#>
             <reason-code> [<optional-info>]
             An error occurred within  a  breakpoint  command  list.
             The given 16-bit sequence-number refers to the sequence
             number  of  the  CREATE  command   that   created   the
             breakpoint,  while  breakpoint-sequence#  refers to the
             sequence number of the command  within  the  breakpoint
             given by <breakpoint-descriptor>.
   5.8  ERRACK Acknowledgement
        An  ERRACK  is sent by the host  in  response  to  an  ERROR
   reply  from  the  target.  The ERRACK is used to acknowledge that
   the host has received the ERROR reply.
                                                             Page 39
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               4               |
                    +---------------+---------------+
                  1 |   PROTOCOL    |    ERRACK     |
                    +---------------+---------------+
                         ERRACK Command Format
                               Figure 25
   Page 40
   LDP Specification                          Data Transfer Commands
                               CHAPTER 6
                        Data Transfer Commands
        Data transfer commands  transfer data between the  host  and
   the  target.  These commands are used for loading and dumping the
   target, and examining and depositing  locations  on  the  target.
   The  READ  command  reads  data from the target, the MOVE command
   moves data within the  target  or  from  the  target  to  another
   entity,  and  the  WRITE  command  writes  data  to  the  target.
   REPEAT_DATA makes copies of a pattern to  the  target  --  it  is
   useful  for  zeroing memory.  WRITE_MASK writes data with a mask,
   and is intended for modifying target  parameter tables.
        Data transmitted to  and from the target always  contains  a
   target  address.   In  writes  to the target, this is used as the
   destination of the data.  In reads from the  target,  the  target
   address  is  used by the host to identify where in the target the
   data came from.  In addition, the  MOVE  command  may  contain  a
   'host'  address  as  its  destination;  this  permits the host to
   further discriminate between possible sources of  data  from  the
   target -- from different breakpoints, debugging windows, etc.
        A read request to  the  target  may  generate  one  or  more
   response  messages.   In  particular,  responses  to requests for
   large amounts of data -- core  dumps,  for  example  --  must  be
   broken  up into multiple messages, if the block of data requested
   plus the LDP header exceeds the transport layer message size.
        In commands which contain data (WRITE, READ_DATA,  MOVE_DATA
   and REPEAT_DATA), if there are an odd number of data octets, then
   a  null octet is appended.  This is so that the next  command  in
   the  message,  if  any, will begin on an even octet.  The command
   length is the sum of the number of octets in the  command  header
   and  the  number  of octets of data, excluding the null octet, if
   any.
        The addressing formats which may be used with data  transfer
   commands  are  specified for each LDP session at the start of the
   session by the target  in  the  HELLO_REPLY  response.   See  the
   section  entitled  'Addressing',  above, for a description of LDP
   addressing formats and modes.   In  the  command  diagrams  given
   below,  the  short  addressing  format  is  illustrated.  For LDP
   sessions using long addressing, addresses are  five  words  long,
                                                             Page 41
   RFC-909                                                 July 1984
   instead of three words, as shown here.  In both addressing modes,
   descriptors are three words and offsets are two words.
   6.1  WRITE Command
        The WRITE command is used to send octets of  data  from  the
   host  to  the  target.  This command specifies the address in the
   target where the data is to be stored, followed by  a  stream  of
   data  octets.   If  the  data  stream  contains  an odd number of
   octets, then a  null octet is appended so that the next  command,
   if  any,  will  begin  on  an even octet.  Since LDP must observe
   message size limitations  imposed  by  the  underlying  transport
   layer,  a  single  logical  write  may  need to be broken up into
   multiple WRITEs in separate transport messages.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 | DATA_TRANSFER |    WRITE      |
                    +---------------+---------------+
                  2 |                               |
                    +--          Target           --+
                  3 |            Start              |
                    +--          Address          --+
                  4 |                               |
                    +---------------+---------------+
                  5 |  Data Octet   |  Data Octet   |
                    +---------------+---------------+
                                    *
                                    *
                                    *
                    +---------------+---------------+
                  n |  Data Octet   | Data or Null  |
                    +---------------+---------------+
                         WRITE Command Format
                               Figure 26
   Page 42
   LDP Specification                          Data Transfer Commands
   WRITE FIELDS:
   Command Length
        The command  length  gives  the  number  of  octets  in  the
        command,  including  data  octets, but excluding the padding
        octet, if any.
   Target Start Address
        This is the address to begin storing  data  in  the  target.
        The  length  of the data to be stored may be inferred by the
        target from the command length.  An illegal address or range
        will generate an ERROR reply.
   Data Octets
        Octets of data to be stored in the target.  Data are  packed
        according  to  the packing convention described above.  Ends
        with a null octet if there are an odd number of data octets.
   6.2  READ Command
        The host uses the READ command  to   ask   the   target   to
   send  back  a contiguous block of data.  The data is specified by
   a target starting address and a count.  The  target  returns  the
   data  in  one or more READ_DATA commands, which give the starting
   address (in the target) of each segment of returned  data.   When
   the  transfer  is completed, the target sends a READ_DONE command
   to the host.
                                                             Page 43
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               14              |
                    +---------------+---------------+
                  1 | DATA_TRANSFER |    READ       |
                    +---------------+---------------+
                  2 |                               |
                    +--          Target           --+
                  3 |            Start              |
                    +--          Address          --+
                  4 |                               |
                    +---------------+---------------+
                  5 |            Address            |
                    +--          Unit             --+
                  6 |            Count              |
                    +---------------+---------------+
                          READ Command Format
                               Figure 27
   READ FIELDS:
   Target Start Address
        The starting address of the requested block of target  data.
        The  target  sends an ERROR reply if the starting address is
        illegal, if the ending address computed from the sum of  the
        start  and the count is illegal, or if holes are encountered
        in the middle of the range.
   Address Unit Count
        The count of the number  of  target  indivisibly-addressable
        units  to be transferred.  For example, if the address space
        is PHYS_MACRO, a count of two and a start  address  of  1000
        selects the contents of locations 1000 and 1001.  'Count' is
        used instead of 'length' to avoid the problem of determining
        units  the  length  should be denominated in (octets, words,
        etc.).  The size and type of the unit will vary depending on
        the address space selected by the target start address.  The
        target should  reply  with  an  error  (if  it  is  able  to
   Page 44
   LDP Specification                          Data Transfer Commands
        determine  in  advance of a transfer) if the inclusive range
        of addresses specified by the start address  and  the  count
        contains an illegal or nonexistent address.
   6.3  READ_DATA Response
        The target uses the  READ_DATA  response  to  transmit  data
   requested  by  a  host  READ  command.   One  or  more  READ_DATA
   responses  may  be  needed  to  fulfill  a  given  READ  command,
   depending  on  the  size  of  the  data  block  requested and the
   transport layer message size  limits.   Each  READ_DATA  response
   gives the target starting address of its segment of data.  If the
   response contains an odd number of data octets, the  target  ends
   the response with a null octet.
                                                             Page 45
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 | DATA_TRANSFER |    READ_DATA  |
                    +---------------+---------------+
                  2 |                               |
                    +--          Target           --+
                  3 |            Start              |
                    +--          Address          --+
                  4 |                               |
                    +---------------+---------------+  +-+
                  5 |  Data Octet   |  Data Octet   |   |
                    +---------------+---------------+   |
                                    *                   |
                                    *                   | Data
                                    *                   |
                    +---------------+---------------+   |
                  n |  Data Octet   | Data or Null  |   |
                    +---------------+---------------+  +-+
                         DATA Response Format
                               Figure 28
   READ_DATA FIELDS:
   Command Length
        The command  length  gives  the  number  of  octets  in  the
        command,  including  data  octets, but excluding the padding
        octet, if any.  The host can calculate  the  length  of  the
        data  by  subtracting  the  header  length  from the command
        length.  Since the target address may be either three  words
        (short format) or five words (long format), the address mode
        must be checked to determine which is being used.
   Target Start Address
        This is the starting address of the  data  segment  in  this
        message.  The host may infer the length of the data from the
        command length.  The address format (short or long)  is  the
   Page 46
   LDP Specification                          Data Transfer Commands
        same as on the initial READ command.
   Data Octets
        Octets of data from the target.  Data are  packed  according
        to the packing convention described above.  Ends with a null
        octet if there are an odd number of data octets.
   6.4  READ_DONE Reply
        The target sends a READ_DONE reply to the host after it  has
   finished  transferring  the  data  requested  by  a READ command.
   READ_DONE specifies the sequence number of the READ command.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               6               |
                    +---------------+---------------+
                  1 | DATA_TRANSFER |    READ_DONE  |
                    +---------------+---------------+
                  2 |      READ Sequence Number     |
                    +---------------+---------------+
                        READ_DONE Reply Format
                               Figure 29
   READ_DONE FIELDS:
   READ Sequence Number
        The sequence number of the READ command this is a reply to.
                                                             Page 47
   RFC-909                                                 July 1984
   6.5  MOVE Command
        The MOVE command is sent by the host to move a block of data
   from  the  target  to  a  specified destination.  The destination
   address may specify a location in the target, in the host, or  in
   another  target  (for loading one target from another).  The data
   is specified by a target starting address  and  an  address  unit
   count.   The  target sends an ERROR reply if the starting address
   is illegal, if the ending address computed from the  sum  of  the
   start  and  the  count is illegal, or if holes are encountered in
   the middle of the range.  If the MOVE destination is  off-target,
   the  target  moves the data in one or MOVE_DATAs.  Other commands
   arriving at the target during the transfer should be processed in
   a  timely fashion, particularly the ABORT command.  When the data
   has been moved,  the  target  sends  a  MOVE_DONE  to  the  host.
   However,   a  MOVE  within  a  breakpoint  will  not  generate  a
   MOVE_DONE.
        A MOVE with a host destination differs from a READ  in  that
   it contains a host address.  This field is specified  by the host
   in the MOVE command and copied by the target into the  responding
   MOVE_DATA(s).   The   address   may   be  used  by  the  host  to
   differentiate data returned from multiple  MOVE  requests.   This
   information   may  be  useful  in  breakpoints,  in  multi-window
   debugging  and  in  communication  with  targets  with   multiple
   processors.   For example, the host sends the MOVE command to the
   target to  be  executed  during  a breakpoint.  The ID  field  in
   the  host address might be an index into a host breakpoint table.
   When the breakpoint executes,  the  host  would  use  the  ID  to
   associate the returning MOVE_DATA with this breakpoint.
   Page 48
   LDP Specification                          Data Transfer Commands
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 | DATA_TRANSFER |    MOVE       |
                    +---------------+---------------+
                  2 |                               |
                    +--          Source           --+
                  3 |            Start              |
                    +--          Address          --+
                  4 |                               |
                    +---------------+---------------+
                  5 |            Address            |
                    +--          Unit             --+
                  6 |            Count              |
                    +---------------+---------------+
                  7 |                               |
                    +--          Destination      --+
                  8 |            Start              |
                    +--          Address          --+
                  9 |                               |
                    +---------------+---------------+
                          MOVE Command Format
                               Figure 30
   MOVE  FIELDS:
   Source Start Address
        The starting address of the requested block of target  data.
        An illegal address type will generate an error reply.
   Address Unit Count
        The count of the number  of  target  indivisibly-addressable
        units  to be transferred.  For example, if the address space
        is PHYS_MACRO, a count of two and a start  address  of  1000
        selects the contents of locations 1000 and 1001.  'Count' is
        used instead of 'length' to avoid the problem of determining
        units  the  length  should be denominated in (octets, words,
                                                             Page 49
   RFC-909                                                 July 1984
        etc.).  The size and type of the unit will vary depending on
        the address space selected by the target start address.  The
        target should  reply  with  an  error  (if  it  is  able  to
        determine  in  advance of a transfer) if the inclusive range
        of addresses specified by the start address  and  the  count
        contains an illegal or nonexistent address.
   Destination Address
        The destination of the MOVE.  If the address space is on the
        target,  the address unit size should agree with that of the
        source address space.  If the address  mode  is  HOST,   the
        values  and  interpretations of the remaining address fields
        are   arbitrary,   and   are   determined   by   the    host
        implementation.    For  example,  the  mode  argument  might
        specify a table (breakpoint, debugging window, etc.) and the
        ID field an index into the table.
   6.6  MOVE_DATA Response
        The target uses the MOVE_DATA  responses  to  transmit  data
   requested  by  a  host  MOVE  command.   One  or  more  MOVE_DATA
   responses  may  be  needed  to  fulfill  a  given  MOVE  command,
   depending  on  the  size  of  the  data  block  requested and the
   transport layer message size  limits.   Each  MOVE_DATA  response
   gives the target starting address of its segment of data.  If the
   response contains an odd number of data octets, the target should
   end the response with a null octet.
   Page 50
   LDP Specification                          Data Transfer Commands
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 | DATA_TRANSFER |    MOVE_DATA  |
                    +---------------+---------------+
                  2 |                               |
                    +--          Source           --+
                  3 |            Start              |
                    +--          Address          --+
                  4 |                               |
                    +---------------+---------------+
                  5 |                               |
                    +--          Destination      --+
                  6 |            Start              |
                    +--          Address          --+
                  7 |                               |
                    +---------------+---------------+    +-+
                  8 |  Data Octet   |  Data Octet   |     |
                    +---------------+---------------+     |
                                    *                     |
                                    *                     | Data
                                    *                     |
                    +---------------+---------------+     |
                  n |  Data Octet   | Data or Null  |     |
                    +---------------+---------------+    +-+
                       MOVE_DATA Response Format
                               Figure 31
   MOVE_DATA FIELDS:
   Command Length
        The command  length  gives  the  number  of  octets  in  the
        command,  including  data  octets, but excluding the padding
        octet, if any.
   Source Start Address
        This is the starting address of the  data  segment  in  this
                                                             Page 51
   RFC-909                                                 July 1984
        message.   The  host  may  infer length of the data from the
        command length.
   Destination Address
        The destination address copied from the  MOVE  command  that
        initiated this transfer.  In the case of HOST MOVEs, this is
        used by the host to identify the source of the data.
   Data Octets
        Octets of data from the target.  Data are  packed  according
        to the packing convention described above.  Ends with a null
        octet if there are an odd number of data octets.
   6.7  MOVE_DONE Reply
        The target sends a MOVE_DONE reply to the host after it  has
   finished  transferring  the  data  requested  by  a MOVE command.
   MOVE_DONE specifies the sequence number of the MOVE command.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               6               |
                    +---------------+---------------+
                  1 | DATA_TRANSFER |    MOVE_DONE  |
                    +---------------+---------------+
                  2 |      MOVE Sequence Number     |
                    +---------------+---------------+
                        MOVE_DONE Reply Format
                               Figure 32
   MOVE_DONE FIELDS:
   MOVE Sequence Number
        The sequence number of the MOVE command this is a reply to.
   Page 52
   LDP Specification                          Data Transfer Commands
   6.8  REPEAT_DATA
        The REPEAT_DATA command is sent by the host to write  copies
   of  a  specified  pattern  into  the  target.   This  provides an
   efficient way of zeroing target memory  and  initializing  target
   data  structures.   The  command  specifies  the  target starting
   address, the number of copies of the pattern to be  made,  and  a
   stream of octets that constitutes the pattern.
        This command differs from the other data  transfer  commands
   in  that  the effect of a REPEAT_DATA with a large pattern cannot
   be duplicated by sending the data in smaller chunks over  several
   commands.   Therefore,  the maximum size of a pattern that can be
   copied with REPEAT_DATA will depend on the message size limits of
   the transport layer.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 | DATA_TRANSFER | REPEAT_DATA   |
                    +---------------+---------------+
                  2 |                               |
                    +--          Target           --+
                  3 |            Start              |
                    +--          Address          --+
                  4 |                               |
                    +---------------+---------------+
                  6 |         Repeat Count          |
                    +---------------+---------------+  +-+
                  7 |  Data Octet   |  Data Octet   |   |
                    +---------------+---------------+   |
                                    *                   |
                                    *                   | Pattern
                                    *                   |
                    +---------------+---------------+   |
                  n |  Data Octet   | Data or Null  |   |
                    +---------------+---------------+  +-+
                      REPEAT_DATA Command Format
                               Figure 33
                                                             Page 53
   RFC-909                                                 July 1984
   REPEAT_DATA FIELDS:
   Command Length
        The command  length  gives  the  number  of  octets  in  the
        command, including data octets in the pattern, but excluding
        the padding octet, if any.
   Target Start Address
        This is the starting address where the  first  copy  of  the
        pattern  should be written in the target.  Successive copies
        of the  pattern  are  made  contiguously  starting  at  this
        address.
   Repeat Count
        The repeat count specifies  the  number  of  copies  of  the
        pattern that should be made in the target.  The repeat count
        should be greater than zero.
   Pattern
        The pattern to be copied into  the  target,  packed  into  a
        stream  of octets.  Data are packed according to the packing
        convention described above.  Ends with a null octet if there
        are an odd number of data octets.
   6.9  WRITE_MASK Command (Optional)
        The host sends a WRITE_MASK command to the target  to  write
   one  or  more  masked  values.   The  command  uses an address to
   specify a target base location, followed by one or  more  offset-
   mask-value triplets.  Each triplet gives an offset from the base,
   a value, and a mask indicating which bits in the location at  the
   offset are to be changed.
        This optional command is intended for use in controlling the
   target  by changing locations in a table.  For example, it may be
   used  to  change  entries  in  a  target  parameter  table.   The
   operation  of  modifying a specified location with a masked value
   is intended to be atomic.  In other words, another target process
   should  not be able to access the location to be modified between
   Page 54
   LDP Specification                          Data Transfer Commands
   the start and the end of the modification.
                                                             Page 55
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 | DATA_TRANSFER | WRITE_MASK    |
                    +---------------+---------------+
                  2 |                               |
                    +--          Target           --+
                  3 |            Base               |
                    +--          Address          --+
                  4 |                               |
                    +---------------+---------------+   +-+
                  5 |                               |    |
                    +--          Offset           --+    |
                  6 |                               |    |
                    +---------------+---------------+    | Offset-Mask-Value
                  7 |                               |    | Triplet
                    +--          Mask             --+    |
                  8 |                               |    |
                    +---------------+---------------+    |
                  9 |                               |    |
                    +--          Value            --+    |
                  10|                               |    |
                    +---------------+---------------+   +-+
                                    *
                                    *
                                    *
                    +---------------+---------------+   +-+
                    |                               |    |
                    +--          Offset           --+    |
                    |                               |    |
                    +---------------+---------------+    | Offset-Mask-Value
                    |                               |    | Triplet
                    +--          Mask             --+    |
                    |                               |    |
                    +---------------+---------------+    |
                    |                               |    |
                    +--          Value            --+    |
                    |                               |    |
                    +---------------+---------------+   +-+
                           WRITE_MASK Format
                               Figure 34
   Page 56
   LDP Specification                          Data Transfer Commands
   WRITE_MASK FIELDS:
   Command Length
        The command  length  gives  the  number  of  octets  in  the
        command.  The number of offset-value pairs may be calculated
        from this, since the command  header  is  either  10  or  12
        octets  long  (short  or  long  address  format),  and  each
        offset-mask-value triplet is 12 octets long.
   Target Base Address
        Specifies the target location to which the offset  is  added
        to yield the location to be modified.
   Offset
        An offset to be added to the base to select a location to be
        modified.
   Mask
        Specifies which bits in the value are to be copied into  the
        location.
   Value
        A value to be stored at the specified offset from the  base.
        The  set  bits in the mask determine which bits in the value
        are applied to the location.  The following  algorithm  will
        achieve  the  intended result:  take the one's complement of
        the mask and AND it with the location, leaving the result in
        the  location.   Then AND the mask and the value, and OR the
        result into the location.
                                                             Page 57
   RFC-909                                                 July 1984
   Page 58
   LDP Specification                                Control Commands
                               CHAPTER 7
                           Control Commands
        Control commands are used to control the execution of target
   code,  breakpoints  and  watchpoints.  They are also used to read
   and report  the  state  of  these  objects.   The  object  to  be
   controlled  or reported on is specified with a descriptor.  Valid
   descriptor modes include PHYS_* (for some commands) PROCESS_CODE,
   BREAKPOINT  and  WATCHPOINT.   Control  commands which change the
   state of the target are START, STOP, CONTINUE and  STEP.   REPORT
   requests  a  STATUS  report  on  a target object.  EXCEPTION is a
   spontaneous report on an  object,  used  to  report  asynchronous
   events such as hardware traps.  The host may verify the action of
   a START, STOP, STEP or CONTINUE command by following  it  with  a
   REPORT command.
   7.1  START Command
        The START command is sent by the host to start execution  of
   a  specified  object  in  the  target.  For targets which support
   multiple processes, a PROCESS_CODE address specifies the  process
   to  be  started.  Otherwise, one of the  PHYS_* modes may specify
   a location  in  macro-memory  where  execution  is  to  continue.
   Applied  to  a  breakpoint or watchpoint, START sets the value of
   the object's state variable, and activates the  breakpoint.   The
   breakpoint counter and pointer variables are initialized to zero.
                                                             Page 59
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               14              |
                    +---------------+---------------+
                  1 |   CONTROL     |     START     |
                    +---------------+---------------+  +-+
                  2 |    Mode       |     0         |   |
                    +---------------+---------------+   |
                  3 |                               |   |
                    +--            ID             --+   |
                  4 |              Field            |   |  Address
                    +-------------------------------+   |
                  5 |                               |   |
                    +--            Offset         --+   |
                  6 |                               |   |
                    +-------------------------------+  +-+
                         START Command Format
                               Figure 35
   START FIELDS:
   Address
        The descriptor specifies the object to be started.   If  the
        mode  is  PROCESS_CODE,  ID  specifies  the  process  to  be
        started, and offset gives the  process  virtual  address  to
        start at.  If the mode is PHYS_*, execution of the target is
        continued at the specified address.
        For modes of BREAKPOINT and WATCHPOINT, the offset specifies
        the  new  value  of the FSM state variable.  This is for FSM
        breakpoints and watchpoints.
   Page 60
   LDP Specification                                Control Commands
   7.2  STOP Command
        The STOP command is sent by the host to stop execution of  a
   specified  object  in  the  target.   A  descriptor specifies the
   object. Applied to a breakpoint or watchpoint,  STOP  deactivates
   it.   The  breakpoint/watchpoint may be re-activated by issuing a
   START or a CONTINUE command for it.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               10              |
                    +---------------+---------------+
                  1 |   CONTROL     |     STOP      |
                    +---------------+---------------+  +-+
                  2 |    Mode       |     0         |   |
                    +---------------+---------------+   |
                  3 |                               |   |  Descriptor
                    +--            ID             --+   |
                  4 |              Field            |   |
                    +-------------------------------+  +-+
                          STOP Command Format
                               Figure 36
   STOP FIELDS:
   Descriptor
        The  descriptor  specifies  the  object  to  be  stopped  or
        disarmed.  If the mode is PROCESS_CODE, the ID specifies the
        process to be stopped.
        For  modes  of  BREAKPOINT  and  WATCHPOINT,  the  specified
        breakpoint  or  watchpoint  is  deactivated.   It may be re-
        activated by a CONTINUE or START command.
                                                             Page 61
   RFC-909                                                 July 1984
   7.3  CONTINUE Command
        The CONTINUE command is sent by the host to resume execution
   of  a specified object in the target.  A descriptor specifies the
   object. Applied to a breakpoint or watchpoint, CONTINUE activates
   it.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               10              |
                    +---------------+---------------+
                  1 |   CONTROL     |     CONTINUE  |
                    +---------------+---------------+  +-+
                  2 |    Mode       |     0         |   |
                    +---------------+---------------+   |
                  3 |                               |   |  Descriptor
                    +--            ID             --+   |
                  4 |              Field            |   |
                    +-------------------------------+  +-+
                        CONTINUE Command Format
                               Figure 37
   CONTINUE FIELDS:
   Descriptor
        The descriptor specifies the object to be resumed or  armed.
        If the mode is PROCESS_CODE, the ID specifies the process to
        be resumed.
        For  modes  of  BREAKPOINT  and  WATCHPOINT,  the  specified
        breakpoint or watchpoint is armed.
   7.4  STEP Command
        The STEP command is sent by the  host  to  the  target.   It
   requests   the  execution  of  one  instruction  (or  appropriate
   operation) in the object specified by the descriptor.
   Page 62
   LDP Specification                                Control Commands
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               10              |
                    +---------------+---------------+
                  1 |   CONTROL     |     STEP      |
                    +---------------+---------------+  +-+
                  2 |    Mode       |     0         |   |
                    +---------------+---------------+   |
                  3 |                               |   |  Descriptor
                    +--            ID             --+   |
                  4 |              Field            |   |
                    +-------------------------------+  +-+
                          STEP Command Format
                               Figure 38
   STEP FIELDS:
   Descriptor
        The descriptor specifies the object to be stepped.   If  the
        mode is PROCESS_CODE, the ID specifies a process.
   7.5  REPORT Command
        The REPORT command is sent by the host to request  a  status
   report on a specified target object.  The status is returned in a
   STATUS reply.
                                                             Page 63
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               10              |
                    +---------------+---------------+
                  1 |   CONTROL     |     REPORT    |
                    +---------------+---------------+  +-+
                  2 |    Mode       |     0         |   |
                    +---------------+---------------+   |
                  3 |                               |   |  Descriptor
                    +--            ID             --+   |
                  4 |              Field            |   |
                    +-------------------------------+  +-+
                         REPORT Command Format
                               Figure 39
   REPORT FIELDS:
   Descriptor
        The descriptor specifies  the  object  for  which  a  STATUS
        report  is  requested.   For  a mode of PROCESS_CODE, the ID
        specifies a process.  Other valid modes are  PHYS_MACRO,  to
        query  the  status of the target application, and BREAKPOINT
        and WATCHPOINT,  to  get  the  status  of  a  breakpoint  or
        watchpoint.
   7.6  STATUS Reply
        The target sends a STATUS reply  in  response  to  a  REPORT
   command  from  the  host.   STATUS gives the state of a specified
   object.  For example, it may tell  whether  a  particular  target
   process is running or stopped.
   Page 64
   LDP Specification                                Control Commands
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |         Command Length        |
                    +---------------+---------------+
                  1 |   CONTROL     |     STATUS    |
                    +---------------+---------------+  +-+
                  2 |    Mode       |     0         |   |
                    +---------------+---------------+   |
                  3 |                               |   |  Descriptor
                    +--            ID             --+   |
                  4 |              Field            |   |
                    +-------------------------------+  +-+
                  5 |              Status           |
                    +-------------------------------+  +-+
                                    *                   |
                                    *                   |
                                    *                   |  Other Data
                    +-------------------------------+   |
                  n |        Other Data             |   |
                    +-------------------------------+  +-+
                          STATUS Reply Format
                               Figure 40
   STATUS FIELDS:
   Descriptor
        The descriptor specifies the object whose  status  is  being
        given.  If the mode is PROCESS_CODE, then the ID specifies a
        process.  If the mode is PHYS_MACRO, then the status is that
        of the target application.
   Status
        The status code describes the status of the object.   Status
        codes  are  0=STOPPED  and  1=RUNNING.   For breakpoints and
        watchpoints, STOPPED means disarmed and RUNNING means armed.
   Other Data
        For breakpoints and watchpoints, Other Data  consists  of  a
                                                             Page 65
   RFC-909                                                 July 1984
        16-bit  word  giving  the  current  value  of  the FSM state
        variable.
   7.7  EXCEPTION Trap
        An EXCEPTION is a spontaneous message sent from  the  target
   indicating   a   target-machine   exception   associated  with  a
   particular object. The object is specified by an address.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |         Command Length        |
                    +---------------+---------------+
                  1 |   CONTROL     |   EXCEPTION   |
                    +---------------+---------------+  +-+
                  2 |    Mode       |     0         |   |
                    +---------------+---------------+   |
                  3 |                               |   |
                    +--            ID             --+   |
                  4 |              Field            |   |  Address
                    +-------------------------------+   |
                  5 |                               |   |
                    +--            Offset         --+   |
                  6 |                               |   |
                    +-------------------------------+  +-+
                  7 |              Type             |
                    +-------------------------------+  +-+
                                    *                   |
                                    *                   |
                                    *                   |  Other Data
                    +-------------------------------+   |
                  n |        Other Data             |   |
                    +-------------------------------+  +-+
                           EXCEPTION Format
                               Figure 41
   EXCEPTION FIELDS:
   Address
   Page 66
   LDP Specification                                Control Commands
        The address specifies the object the exception is for.
   Type
        The type of exception.  Values are target-dependent.
   Other Data
        Values are target-dependent.
                                                             Page 67
   RFC-909                                                 July 1984
   Page 68
   LDP Specification                             Management Commands
                               CHAPTER 8
                          Management Commands
        Management commands are used to  control  resources  in  the
   target  machine.   There  are  two kinds of commands:  those that
   interrogate the remote machine about resources,  and  those  that
   allocate  and  free  resources.  There are management commands to
   create,  list  and  delete  breakpoints.    All   commands   have
   corresponding  replies  which  include the sequence number of the
   request command.  Failing requests produce ERROR replies.
        There are  two  resource  allocation  commands,  CREATE  and
   DELETE,  which  create  and delete objects in the remote machine.
   There are a number of listing commands for listing a  variety  of
   target objects -- breakpoints, watchpoints, processes, and names.
   The amount of data returned  by  listing  commands  may  vary  in
   length,  depending  on the state of the target.  If a list is too
   large to fit in a single message, the  target  will  send  it  in
   several  list  replies.   A  flag in each reply specifies whether
   more messages are to follow.
   8.1  CREATE Command
        The CREATE command is sent from the host to  the  target  to
   create  a target object.  If the CREATE is successful, the target
   returns  a  CREATE_DONE  reply,  which  contains   a   descriptor
   associated  with  the  CREATEd object.  The types of objects that
   may be specified in  a  CREATE  include  breakpoints,  processes,
   memory  objects  and  descriptors.   All  are optional except for
   breakpoints.
                                                             Page 69
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 | MANAGEMENT    |     CREATE    |
                    +---------------+---------------+
                  2 |           Create Type         |
                    +---------------+---------------+   +-+
                                    *                    |
                                    *                    |  Create
                                    *                    |  Arguments
                    +---------------+---------------+    |
                  n |         Create Arguments      |    |
                    +---------------+---------------+   +-+
                         CREATE Command Format
                               Figure 42
   CREATE FIELDS:
   Create Type
        The type of object to be created.  Arguments vary  with  the
        type.   Currently defined types are shown in Figure 43.  All
        are optional except for BREAKPOINT.
                  Create Type  |  Symbol
                  -------------+----------------
                     0            BREAKPOINT
                     1            WATCHPOINT
                     2            PROCESS
                     3            MEMORY_OBJECT
                     4            DESCRIPTOR
                             Create Types
                               Figure 43
   Page 70
   LDP Specification                             Management Commands
   Create Arguments
        Create arguments depend on the type of object being created.
        The formats for each type of object are described below.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               22              |
                    +---------------+---------------+
                  1 |   MANAGEMENT  |     CREATE    |
                    +---------------+---------------+
                  2 |           BREAKPOINT          |
                    +---------------+---------------+  +-+
                  3 |    Mode       | Mode Argument |   |
                    +---------------+---------------+   |
                  4 |                               |   |
                    +--            ID             --+   |  Create
                  5 |              Field            |   |  BREAKPOINT
                    +-------------------------------+   |  Arguments
                  6 |                               |   |
                    +--            Offset         --+   |
                  7 |                               |   |
                    +-------------------------------+   |
                  8 |        Maximum States         |   |
                    +---------------+---------------+   |
                  9 |        Maximum Size           |   |
                    +---------------+---------------+   |
                  10|     Maximum Local Variables   |   |
                    +---------------+---------------+  +-+
                       CREATE BREAKPOINT Format
                               Figure 44
   BREAKPOINT and WATCHPOINT
        The format  is the same for  CREATE  BREAKPOINT  and  CREATE
        WATCHPOINT.   In  the following discussion, 'breakpoint' may
        be taken to mean either breakpoint or watchpoint.
        The address is the location where the breakpoint  is  to  be
        set.   In  the  case of watchpoints it is the location to be
                                                             Page 71
   RFC-909                                                 July 1984
        watched.  Valid modes are any  PHYS_*  mode  that  addresses
        macro-memory,  PROCESS_CODE for breakpoints and PROCESS_DATA
        for watchpoints.
        'Maximum states' is the number of states  the  finite  state
        machine  for  this  breakpoint  will  have.  A value of zero
        indicates a default breakpoint, for  targets  which  do  not
        implement finite state machine (FSM) breakpoints.  A default
        breakpoint is the same as an FSM with one  state  consisting
        of  a  STOP  and a REPORT command for the process containing
        the breakpoint.
        'Maximum  size'  is  the  total  size,  in  octets,  of  the
        breakpoint  data  to  be sent via subsequent BREAKPOINT_DATA
        commands.  This is the size of the data only, and  does  not
        include the LDP command headers and breakpoint descriptors.
        'Maximum local variables' is the number of 32-bit  longs  to
        reserve  for  local variables for this breakpoint.  Normally
        this value will be zero.
   PROCESS
        Creates a new process.  Arguments are target-dependent.
   Page 72
   LDP Specification                             Management Commands
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 |   MANAGEMENT  |     CREATE    |
                    +---------------+---------------+
                  2 |         MEMORY_OBJECT         |
                    +---------------+---------------+
                  3 |         Object Size           |
                    +---------------+---------------+
                  4 |           Name Size           |
                    +-------------------------------+  +-+
                  5 |    Name char  |  Name char    |   |
                    +-------------------------------+   |
                                    *                   |  Object
                                    *                   |  Name
                                    *                   |
                    +---------------+---------------+   |
                  n | 0 or Name char|       0       |   |
                    +---------------+---------------+  +-+
                      CREATE MEMORY_OBJECT Format
                               Figure 45
   MEMORY_OBJECT
        Creates an object of size Object Size, with the given  name.
        Object  Size  is in target dependent units.  The name may be
        the null string for unnamed objects.  Name  Size  gives  the
        number  of  characters  in  Object  Name,  and must be even.
        Always ends with a null octect.
   DESCRIPTOR
        Used for obtaining descriptors from IDs  on  target  systems
        where  IDs  are  longer  than  32  bits.   There is a single
        argument, Long ID, whose length is target dependent.
                                                             Page 73
   RFC-909                                                 July 1984
   8.2  CREATE_DONE Reply
        The target sends a CREATE_DONE reply to the host in response
   to  a successful CREATE command.  The reply contains the sequence
   number of the CREATE request, and a  descriptor  for  the  object
   created.   This  descriptor  is  used  by the host to specify the
   object in subsequent commands referring to  it.   Commands  which
   refer  to  created  objects  include  LIST_* commands, DELETE and
   BREAKPOINT_DATA.  For example, to delete a  CREATEd  object,  the
   host  sends  a  DELETE  command  that  specifies  the  descriptor
   returned by the CREATE_DONE reply.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               12              |
                    +---------------+---------------+
                  1 |   MANAGEMENT  |  CREATE_DONE  |
                    +---------------+---------------+
                  2 |     Create Sequence Number    |
                    +---------------+---------------+  +-+
                  3 |    Mode       | Mode Argmuent |   |
                    +---------------+---------------+   |  Created
                  4 |                               |   |  Object
                    +--            ID             --+   |  Descriptor
                  5 |              Field            |   |
                    +---------------+---------------+  +-+
                       CREATE_DONE Reply Format
                               Figure 46
   CREATE_DONE FIELDS:
   Create Sequence Number
        The sequence number of the CREATE command to which  this  is
        the reply.
   Created Object Descriptor
        A descriptor assigned by the target to the  created  object.
        The  contents  of  the  descriptor  fields  are  arbitrarily
   Page 74
   LDP Specification                             Management Commands
        assigned by the target at its convenience.  The host  treats
        the  descriptor  as  a unitary object, used for referring to
        the created object in subsequent commands.
   8.3  DELETE Command
        The host sends a DELETE command to remove an object  created
   by  an  earlier  CREATE  command.   The  object  to be deleted is
   specified  with  a  descriptor.   The  descriptor  is  from   the
   CREATE_DONE reply to the original CREATE command.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               10              |
                    +---------------+---------------+
                  1 |   MANAGEMENT  |    DELETE     |
                    +---------------+---------------+  +-+
                  2 |    Mode       | Mode Argument |   |
                    +---------------+---------------+   |
                  3 |                               |   |  Created
                    +--            ID             --+   |  Object
                  4 |              Field            |   |  Descriptor
                    +---------------+---------------+  +-+
                         DELETE Command Format
                               Figure 47
   DELETE FIELDS:
        Created Object Descriptor
        Specifies the object to be deleted.  This is the  descriptor
        that  was returned by the target in the CREATE_DONE reply to
        the original CREATE command.
                                                             Page 75
   RFC-909                                                 July 1984
   8.4  DELETE_DONE Reply
        The target sends a DELETE_DONE reply to the host in response
   to  a successful DELETE command.  The reply contains the sequence
   number of the DELETE request.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               6               |
                    +---------------+---------------+
                  1 |   MANAGEMENT  | DELETE_DONE   |
                    +---------------+---------------+
                  2 |     Delete Sequence Number    |
                    +---------------+---------------+
                       DELETE_DONE Reply Format
                               Figure 48
   DELETE_DONE FIELDS:
   Request Sequence Number
        The sequence number of the DELETE command to which  this  is
        the reply.
   8.5  LIST_ADDRESSES Command
        The host sends a LIST_ADDRESSES command to request a list of
   valid address ranges for a specified object.  The object is given
   by a descriptor.  Typical objects are a target  process,  or  the
   target   physical   machine.    The   target   responds  with  an
   ADDRESS_LIST reply.  This command is used for obtaining the  size
   of dynamic address spaces and for determining dump ranges.
   Page 76
   LDP Specification                             Management Commands
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               10              |
                    +---------------+---------------+
                  1 |   MANAGEMENT  | LIST_ADDRESSES|
                    +---------------+---------------+  +-+
                  2 |    Mode       | Mode Argument |   |
                    +---------------+---------------+   |  Object
                  3 |                               |   |  Descriptor
                    +--            ID             --+   |
                  4 |              Field            |   |
                    +---------------+---------------+  +-+
                     LIST_ADDRESSES Command Format
                               Figure 49
   LIST_ADDRESSES FIELDS:
        Object Descriptor
        Specifies the object whose address ranges are to be  listed.
        Valid  modes  include  PHYS_MACRO, PHYS_MICRO, PROCESS_CODE,
        and PROCESS_DATA.
   8.6  ADDRESS_LIST Reply
        The target sends  an  ADDRESS_LIST  reply  to  the  host  in
   response  to  a  successful  LIST_ADDRESSES  command.   The reply
   contains the sequence number of the LIST_ADDRESSES  request,  the
   descriptor  of  the  object being listed, and a list of the valid
   address ranges within the  object.
                                                             Page 77
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 |   MANAGEMENT  | ADDRESS_LIST  |
                    +---------------+---------------+
                  2 |      List Sequence Number     |
                    +---------------+---------------+
                  3 |   Flags     |M| Item Count    |
                    +---------------+---------------+
                  4 |                               |
                    +--                           --+
                  5 |          Descriptor           |
                    +--                           --+
                  6 |                               |
                    +---------------+---------------+  +-+
                  7 |                               |   |
                    +--        First Address      --+   | First
                  8 |                               |   | Address
                    +-------------------------------+   | Range
                  9 |                               |   |
                    +--         Last Address      --+   |
                  10|                               |   |
                    +-------------------------------+  +-+
                                    *
                                    *
                                    *
                    +---------------+---------------+  +-+
                    |                               |   |
                    +--        First Address      --+   | Last
                    |                               |   | Address
                    +-------------------------------+   | Range
                    |                               |   |
                    +--         Last Address      --+   |
                    |                               |   |
                    +-------------------------------+  +-+
                       ADDRESS_LIST Reply Format
                               Figure 50
   Page 78
   LDP Specification                             Management Commands
   ADDRESS_LIST FIELDS:
   List Sequence Number
        The sequence number of the LIST_ADDRESSES command  to  which
        this is the reply.
   Flags
        If M=1, the  address  list  is  continued  in  one  or  more
        subsequent  ADDRESS_LIST replies.  If M=0, this is the final
        ADDRESS_LIST.
   Item Count
        The number of address ranges described in this command.
   Descriptor
        The descriptor of the object being listed.
   Address Range
        Each address range is composed of a pair of 32-bit addresses
        which  give  the  first and last addresses of the range.  If
        there are 'holes' in the address space of the  object,  then
        multiple  address  ranges will be used to describe the valid
        address space.
   8.7  LIST_BREAKPOINTS Command
        The host sends a LIST_BREAKPOINTS command to request a  list
   of  all  breakpoints associated with the current connection.  The
   target replies with BREAKPOINT_LIST.
                                                             Page 79
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               4               |
                    +---------------+---------------+
                  1 |   MANAGEMENT  |LIST_BREAKPOINTS
                    +---------------+---------------+
                    LIST_BREAKPOINTS Command Format
                               Figure 51
   8.8  BREAKPOINT_LIST Reply
        The target sends a BREAKPOINT_LIST  reply  to  the  host  in
   response  to  a LIST_BREAKPOINTS command.  The reply contains the
   sequence number of the LIST_BREAKPOINTS request, and  a  list  of
   all  breakpoints  associated  with  the  current connection.  The
   descriptor and address of each breakpoint are listed.
   Page 80
   LDP Specification                             Management Commands
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 |   MANAGEMENT  |BREAKPOINT_LIST|
                    +---------------+---------------+
                  2 |      List Sequence Number     |
                    +---------------+---------------+
                  3 |   Flags     |M| Item Count    |
                    +---------------+---------------+  +-+
                  4 |    Mode       |     0         |   |
                    +---------------+---------------+   |
                  5 |                               |   |  Breakpoint
                    +--            ID             --+   |  Descriptor
                  6 |              Field            |   |
                    +---------------+---------------+  +-+
                  7 |    Mode       | Mode Argument |   |
                    +---------------+---------------+   |
                  8 |                               |   |
                    +--            ID             --+   |  Breakpoint
                  9 |              Field            |   |  Address
                    +-------------------------------+   |
                  10|                               |   |
                    +--            Offset         --+   |
                  11|                               |   |
                    +-------------------------------+  +-+
                                    *                   |  Additional
                                    *                   |  Descriptor-Address
                                    *                   |  Pairs
                                                       +-+
                     BREAKPOINT_LIST Reply Format
                               Figure 52
   BREAKPOINT_LIST FIELDS:
   List Sequence Number
        The sequence number of the LIST_BREAKPOINTS command to which
        this is the reply.
   Flags
                                                             Page 81
   RFC-909                                                 July 1984
        If M=1, the breakpoint list is  continued  in  one  or  more
        subsequent  BREAKPOINT_LIST  replies.   If  M=0, this is the
        final BREAKPOINT_LIST.
   Item Count
        The number of breakpoints described in this list.
   Breakpoint Descriptor
        A descriptor assigned by  the  target  to  this  breakpoint.
        Used   by   the   host   to   specify   this  breakpoint  in
        BREAKPOINT_DATA and DELETE commands.
   Breakpoint Address
        The address at which this breakpoint is set.
   8.9  LIST_PROCESSES Command
        The host sends a LIST_PROCESSES command to request a list of
   descriptors  for all processes on the target.  The target replies
   with PROCESS_LIST.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               4               |
                    +---------------+---------------+
                  1 |   MANAGEMENT  |LIST_PROCESSES |
                    +---------------+---------------+
                     LIST_PROCESSES Command Format
                               Figure 53
   Page 82
   LDP Specification                             Management Commands
   8.10  PROCESS_LIST Reply
        The target  sends  a  PROCESS_LIST  reply  to  the  host  in
   response  to  a  LIST_PROCESSES  command.  The reply contains the
   sequence number of the LIST_PROCESSES request, and a list of  all
   processes  in  the  target.  For each process, a descriptor and a
   target-dependent amount of process data are given.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 |   MANAGEMENT  | PROCESS_LIST  |
                    +---------------+---------------+
                  2 |      List Sequence Number     |
                    +---------------+---------------+
                  3 |   Flags     |M| Item Count    |
                    +---------------+---------------+  +-+
                  4 | PROCESS_CODE  |     0         |   |
                    +---------------+---------------+   |
                  5 |                               |   |  Process
                    +--            ID             --+   |  Descriptor
                  6 |              Field            |   |
                    +---------------+---------------+  +-+
                  7 |       Process data count      |   |
                    +---------------+---------------+   |
                  8 |  Process data |  Process data |   |
                    +-------------------------------+   |  Process
                                    *                   |  Data
                                    *                   |
                                    *                   |
                    +---------------+---------------+   |
                  n |  Process data |  Process data |   |
                    +-------------------------------+  +-+
                                    *                   |  Additional
                                    *                   |  Descriptor-Data
                                    *                   |  Pairs
                                                       +-+
                       PROCESS_LIST Reply Format
                               Figure 54
                                                             Page 83
   RFC-909                                                 July 1984
   PROCESS_LIST FIELDS:
   List Sequence Number
        The sequence number of the LIST_PROCESSES command  to  which
        this is the reply.
   Flags
        If M=1, the  process  list  is  continued  in  one  or  more
        subsequent  PROCESS_LIST replies.  If M=0, this is the final
        PROCESS_LIST.
   Item Count
        The number of processes described in this  list.   For  each
        process  there  is  a  descriptor  and  a variable number of
        octets of process data.
   Process Descriptor
        A descriptor assigned by the target to this  process.   Used
        by the host to specify this PROCESS in a DELETE command.
   Process Data Count
        Number of octets of process data for this process.  Must  be
        even.
   Process Data
        Target-dependent information about this process.  Number  of
        octets is given by the process data count.
   8.11  LIST_NAMES Command
        The host sends a LIST_NAMES command to  request  a  list  of
   available names as strings.  The target replies with NAME_LIST.
   Page 84
   LDP Specification                             Management Commands
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               4               |
                    +---------------+---------------+
                  1 |   MANAGEMENT  | LIST_NAMES    |
                    +---------------+---------------+
                       LIST_NAMES Command Format
                               Figure 55
   8.12  NAME_LIST Reply
        The target sends a NAME_LIST reply to the host  in  response
   to  a LIST_NAMES command.  The reply contains the sequence number
   of the LIST_NAMES request, and a list of  all  target  names,  as
   strings.
                                                             Page 85
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 |   MANAGEMENT  | NAME_LIST     |
                    +---------------+---------------+
                  2 |      List Sequence Number     |
                    +---------------+---------------+
                  3 |   Flags     |M| Item Count    |
                    +---------------+---------------+  +-+
                  4 |           Name Size           |   |
                    +---------------+---------------+   |
                  5 |  Name Char    |   Name Char   |   |  Name
                    +---------------+---------------+   |  String
                                    *                   |
                                    *                   |
                                    *                   |
                    +---------------+---------------+   |
                  n | 0 or Name Char|       0       |   |
                    +---------------+---------------+  +-+
                                    *                   |  Additional
                                    *                   |  Name
                                    *                   |  Strings
                                                       +-+
                        NAME_LIST Reply Format
                               Figure 56
   NAME_LIST FIELDS:
   List Sequence Number
        The sequence number of the LIST_NAMES command to which  this
        is the reply.
   Page 86
   LDP Specification                             Management Commands
   Flags
        If M=1, the name list is continued in one or more subsequent
        NAME_LIST replies.  If M=0, this is the final NAME_LIST.
   Item Count
        The number of name strings in this list.  Each  name  string
        consists  of  a character count and a null-terminated string
        of characters.
   Name Size
        The number of octets in this name string.  Must be even.
   Name Characters
        A string of octets composing the name.   Ends  with  a  null
        octet.   The  number  of  characters must be even, so if the
        terminating null comes on an  odd  octet,  another  null  is
        appended.
   8.13  GET_PHYS_ADDR Command
        The host sends a GET_PHYS_ADDR command to convert an address
   into physical form.  The target returns the physical address in a
   GOT_PHYS_ADDR  reply.   For  example,  the  host  could  send   a
   GET_PHYS_ADDR  command  containing a register-offset address, and
   the target would return the physical address derived from this in
   a GOT_PHYS_ADDR reply.
                                                             Page 87
   RFC-909                                                 July 1984
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               14              |
                    +---------------+---------------+
                  1 |   MANAGEMENT  | GET_PHYS_ADDR |
                    +---------------+---------------+  +-+
                  2 |    Mode       | Mode Argument |   |
                    +---------------+---------------+   |
                  3 |              ID               |   |
                    +--            Field          --+   |
                  4 |                               |   |  Address
                    +---------------+---------------+   |
                  5 |                               |   |
                    +--            Offset         --+   |
                  6 |                               |   |
                    +---------------+---------------+  +-+
                     GET_PHYS_ADDR Command Format
                               Figure 57
   GET_PHYS_ADDR FIELDS:
   Address
        The address to be converted to a physical address.  The mode
        may    be   one   of   PHYS_REG_OFFSET,   PHYS_REG_INDIRECT,
        PHYS_MACRO_PTR, any OBJECT_* mode, and  any  PROCESS_*  mode
        except for PROCESS_REG.
   8.14  GOT_PHYS_ADDR Reply
        The target sends  a  GOT_PHYS_ADDR  reply  to  the  host  in
   response  to  a  successful  GET_PHYS_ADDR  command.   The  reply
   contains the sequence number of the  GET_PHYS_ADDR  request,  and
   the specified address converted into a physical address.
   Page 88
   LDP Specification                             Management Commands
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               16              |
                    +---------------+---------------+
                  1 |   MANAGEMENT  | GOT_PHYS_ADDR |
                    +---------------+---------------+
                  2 |      Get  Sequence Number     |
                    +---------------+---------------+  +-+
                  3 | PHYS_MACRO    |      0        |   |
                    +---------------+---------------+   |
                  4 |                               |   |
                    +--             0             --+   |
                  5 |                               |   |  Address
                    +---------------+---------------+   |
                  6 |                               |   |
                    +--            Offset         --+   |
                  7 |                               |   |
                    +---------------+---------------+  +-+
                      GOT_PHYS_ADDR Reply Format
                               Figure 58
   GOT_PHYS_ADDR FIELDS:
   Get Sequence Number
        The sequence number of the GET_PHYS_ADDR  command  to  which
        this is the reply.
   Address
        The address resulting from translating the address given  in
        the  GET_PHYS_ADDR command into a physical address.  Mode is
        always PHYS_MACRO and ID and mode argument are always  zero.
        Offset gives the 32-bit physical address.
                                                             Page 89
   RFC-909                                                 July 1984
   8.15  GET_OBJECT Command
        The host sends a GET_OBJECT command to convert a name string
   into  a  descriptor.   The  target  returns  the  descriptor in a
   GOT_OBJECT reply.  Intended for use in finding control  parameter
   objects.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |        Command Length         |
                    +---------------+---------------+
                  1 |   MANAGEMENT  | GET_OBJECT    |
                    +---------------+---------------+  +-+
                  2 |           Name Size           |   |
                    +---------------+---------------+   |
                  3 |  Name Char    |   Name Char   |   |  Name
                    +---------------+---------------+   |  String
                                    *                   |
                                    *                   |
                                    *                   |
                    +---------------+---------------+   |
                  n | 0 or Name Char|       0       |   |
                    +---------------+---------------+  +-+
                       GET_OBJECT Command Format
                               Figure 59
   GET_OBJECT FIELDS:
   Name String
        The name of an object.
   Name Size
        The number of octets in this name string.  Must be even.
   Name Characters
        A string of octets composing the name.   Ends  with  a  null
        octet.   The  number  of  characters must be even, so if the
   Page 90
   LDP Specification                             Management Commands
        terminating null comes on an  odd  octet,  another  null  is
        appended.
   8.16  GOT_OBJECT Reply
        The target sends a GOT_OBJECT reply to the host in  response
   to  a  successful  GET_OBJECT  command.   The  reply contains the
   sequence number of the  GET_OBJECT  request,  and  the  specified
   object name converted into a descriptor.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |               12              |
                    +---------------+---------------+
                  1 |   MANAGEMENT  | GOT_OBJECT    |
                    +---------------+---------------+
                  2 |      Get  Sequence Number     |
                    +---------------+---------------+  +-+
                  3 | Mode          | Mode Argument |   |
                    +---------------+---------------+   |
                  4 |                               |   |
                    +--             ID            --+   |  Object
                  5 |                               |   |  Descriptor
                    +---------------+---------------+  +-+
                        GOT_OBJECT Reply Format
                               Figure 60
   GOT_OBJECT FIELDS:
   Get Sequence Number
        The sequence number of the GET_OBJECT command to which  this
        is the reply.
   Descriptor
                                                             Page 91
   RFC-909                                                 July 1984
        The  descriptor  of  the  object  named  in  the  GET_OBJECT
        command.
   Page 92
   LDP Specification                     Breakpoints and Watchpoints
                               CHAPTER 9
                      Breakpoints and Watchpoints
        Breakpoints  and   watchpoints   are   used   in   debugging
   applications.   Each  breakpoint or watchpoint is associated with
   one debugger connection and one address.  When  a  breakpoint  or
   watchpoint is triggered, the target executes one or more commands
   associated with it.  A breakpoint is triggered when  its  address
   is  executed.   A  watchpoint  is  triggered  when its address is
   modified.  The same mechanism is used for structuring  breakpoint
   and  watchpoint  commands.  For brevity's sake, 'breakpoint' will
   be used in the remainder of this document to refer  to  either  a
   breakpoint or a watchpoint.
        The commands used by the host to manipulate breakpoints  are
   given in Figure 61, in the order in which they are normally used.
   All commands are sent from the  host  to  the  target,  and  each
   specifies the descriptor of a breakpoint.
    Command               Description
   ---------------------+------------------------------------
    CREATE                Create a breakpoint
    BREAKPOINT_DATA       Send commands to be executed in an
                          FSM breakpoint
    START                 Activate a breakpoint, set state
                          and initialize breakpoint variables
    STOP                  Deactivate a breakpoint
    CONTINUE              Activate a breakpoint
    LIST_BREAKPOINTS      List all breakpoints
    REPORT                Report the status of a breakpoint
    DELETE                Delete a breakpoint
                  Commands to Manipulate Breakpoints
                               Figure 61
                                                             Page 93
   RFC-909                                                 July 1984
        There are two kinds of breakpoints:  default breakpoints and
   finite state machine (FSM) breakpoints.  They differ in their use
   of commands.
        Default breakpoints  do  not  contain  any  commands.   When
   triggered,  a  default  breakpoint stops the target object (i.e.,
   target process or application) it is located in.  A STATUS report
   on  the  stopped  object is sent to the host.  At this point, the
   host may send further commands to debug the target.
        An FSM breakpoint has one or more conditional command lists,
   organized into a finite state machine.  When an FSM breakpoint is
   created, the total number of states is specified.  The host  then
   sends commands (using BREAKPOINT_DATA) to be associated with each
   state.  The target maintains a state variable for the breakpoint,
   which  determines  which  command  list  will  be executed if the
   breakpoint is triggered.  When  the  breakpoint  is  created  its
   state  variable is initialized to zero (zero is the first state).
   A breakpoint command, SET_STATE, may be used within a  breakpoint
   to  change  the  value  of  the state variable.  A REPORT command
   applied to a breakpoint descriptor returns its  address,  whether
   it is armed or disarmed, and the value of its state variable.
        Commands valid in breakpoints include all  implemented  data
   transfer and control commands, a set of conditional commands, and
   a set of breakpoint commands.  The conditional commands  and  the
   breakpoint  commands  act on a set of local breakpoint variables.
   The  breakpoint  variables  consist  of  the  state  variable,  a
   counter,  and  two  pointer  variables.  The conditional commands
   control the execution of breakpoint command lists  based  on  the
   contents  of  one  of  the  breakpoint variables.  The breakpoint
   commands are used to set the value of the  breakpoint  variables:
   SET_STATE  sets  the  state  variable,  SET_PTR  sets  one of the
   pointer  variables,  and  INC_COUNT  increments  the   breakpoint
   counter.   There may be implementation restrictions on the number
   of breakpoints, the number of states, the number  of  conditions,
   and  the  size  of  the  command  lists.  Management commands and
   protocol commands are forbidden in breakpoints.
        In FSM breakpoints, the execution of commands is  controlled
   as  follows.   When  a  breakpoint is triggered, the breakpoint's
   state  variable  selects  a  particular  state.   One   or   more
   conditional  command  lists  is  associated  with  this state.  A
   conditional  command  list  consists  of  a  list  of  conditions
   followed  by  a  list  of  commands  which  are  executed  if the
   condition list is satisfied.  The debugger starts a breakpoint by
   executing  the  first  of  these lists.  If the condition list is
   Page 94
   LDP Specification                     Breakpoints and Watchpoints
   satisfied, the debugger executes the associated command list  and
   leaves the breakpoint.  If the condition list fails, the debugger
   skips  to  the  next  conditional  command  list.   This  process
   continues  until  the  debugger  either  encounters  a successful
   condition list, or exhausts all the conditional command lists for
   the  state.   The  relationship  of commands, lists and states is
   shown in Figure 62 (IFs,  THENs  and  ELSEs  are  used  below  to
   clarify  the  logical structure within a state; they are not part
   of the protocol).
                  State 0
                          IF <condition list 0>
                             THEN <command list 0>
                          ELSE IF <condition list 1>
                             THEN <command list 1>
                          ELSE IF <condition list n>
                              THEN <command list n>
                          ELSE <exit>
                    *
                    *
                    *
                  State n
                 Breakpoint Conditional Command Lists
                               Figure 62
   9.1  BREAKPOINT_DATA Command
        BREAKPOINT_DATA is a data transfer command used by the  host
   to  send  commands to be executed in breakpoints and watchpoints.
   The command  specifies  the  descriptor  of  the   breakpoint  or
   watchpoint, and a stream of commands to be appended to the end of
   the  breakpoint's  command  list.   BREAKPOINT_DATA  is   applied
   sequentially  to  successive  breakpoint  states,  and successive
                                                             Page 95
   RFC-909                                                 July 1984
   command lists within each state.  Multiple  BREAKPOINT_DATAs  may
   be  sent  for a given breakpoint.  Breaks between BREAKPOINT_DATA
   commands may occur anywhere within the data stream,  even  within
   individual  commands  in the data.  Sufficient space to store the
   data must have been allocated by the maximum size  field  in  the
   CREATE BREAKPOINT/WATCHPOINT command.
                0             0 0   1         1
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
               +---------------+---------------+
             0 |        Command Length         |
               +---------------+---------------+
             1 | DATA_TRANSFER |BREAKPOINT_DATA|
               +---------------+---------------+  +-+
             2 |    Mode       | Mode Argument |   |
               +---------------+---------------+   |  Breakpoint or
             3 |                               |   |  Watchpoint
               +--            ID             --+   |  Descriptor
             4 |              Field            |   |
               +-------------------------------+  +-+
             5 |     Data      |  Data         |   |
               +-------------------------------+   |
                               *                   |
                               *                   |  Data
                               *                   |
               +---------------+---------------+   |
             n |     Data      |  Data or 0    |   |
               +---------------+---------------+  +-+
                    BREAKPOINT_DATA Command Format
                               Figure 63
   BREAKPOINT_DATA FIELDS:
   Command Length
        Total length of this  command  in  octets,  including  data,
        excluding the final padding octet, if any.
   Data
        A stream of data  to  be  appended  to  the  data  for  this
        breakpoint  or  watchpoint.  This stream has the form of one
        or more states, each  containing  one  or  more  conditional
   Page 96
   LDP Specification                     Breakpoints and Watchpoints
        command lists.  The first BREAKPOINT_DATA command sent for a
        breakpoint contains data starting with state zero.  The data
        for  each  state  starts with the state size.  A conditional
        command list is composed of two parts: a condition list, and
        a command list.  Each list begins with a word that gives its
        size in octets.
        <state 0 size>
                 <condition list 0 size> <condition list 0>
                 <command list 0 size>   <command list 0>
                            *
                            *
                            *
                 <condition list n size> <condition list n>
                 <command list n size>   <command list n>
        <state 1 size>
                          <etc>
             *
             *
             *
        <state n size>
                     Breakpoint Data Stream Format
                               Figure 64
                                                             Page 97
   RFC-909                                                 July 1984
   Sizes
        All sizes are stored in 16-bit words, and include their  own
        length.   The state size gives the total number of octets of
        breakpoint data for the  state.   The  condition  list  size
        gives  the total octets of breakpoint data for the following
        condition list.  A condition list size  of  2  indicates  an
        empty  condition  list:  in  this case the following command
        list is executed unconditionally.   The  command  list  size
        gives  the total octets of breakpoint data for the following
        command list.
   Lists
        Condition  and  command  lists  come  in  pairs.   When  the
        breakpoint  occurs,  the condition list controls whether the
        following command list should be executed.  A condition list
        consists  of one or more commands from the CONDITION command
        class.  A command list consists one or  more  LDP  commands.
        Valid   commands  are  any  commands  from  the  BREAKPOINT,
        DATA_TRANSFER or CONTROL command classes.
   Page 98
   LDP Specification                            Conditional Commands
                              CHAPTER 10
                         Conditional Commands
        Conditional commands are used in breakpoints to control  the
   execution  of  breakpoint  commands.   One  or more conditions in
   sequence form a condition list.  If a condition list is satisfied
   (evaluates  to  TRUE),  the  breakpoint  command list immediately
   following it is  executed.   (See  Breakpoints  and  Watchpoints,
   above,  for a discussion of the logic flow in conditional/command
   lists.) Conditional commands perform tests  on  local  breakpoint
   variables,  and  other  locations.   Each  condition evaluates to
   either  TRUE  or  FALSE.   Figure  65  contains  a   summary   of
   conditional commands:
    Command                       Description
   -----------------------------+------------------------------------
   CHANGED <loc>                  Determine if a location has changed
   COMPARE <loc1> <mask> <loc2>   Compare two locations, using a mask
   COUNT_[EQ | GT | LT] <value>   Compare the counter to a value
   TEST  <loc> <mask> <value>     Compare a location to a value
                      Conditional Command Summary
                               Figure 65
   The rules for forming and evaluating condition lists are:
   o   consecutive conditions have an implicit logical  AND  between
       them.  A sequence of such conditions is called an 'and_list'.
       and_lists are delimited by an OR command and by  the  end  of
       the condition list.
   o   the breakpoint OR command may be inserted between any pair of
       conditions
   o   AND takes precedence over OR
   o   nested condition lists are not supported.  A  condition  list
       is simply one or more and_lists, separated by ORs.
                                                             Page 99
   RFC-909                                                 July 1984
   o   the condition list is evaluated in sequence  until  either  a
       TRUE  and_list  is found (condition list <- TRUE), or the end
       of the condition list is reached (condition list  <-  FALSE).
       An and_list is TRUE if all its conditions are TRUE.
   The distillation of these rules into BNF is:
       <condition_list> :== <and_list>  [OR <and_list>]*
       <and_list>       :== <condition> [AND <condition>]*
       <condition>      :== CHANGED | COMPARE | COUNT | TEST
       where:  OR  is a breakpoint command
               AND is implicit for any pair of consecutive conditions
   For example, the following condition list, with one  command  per
   line,
       COUNT_EQ 1
       OR
       COUNT_GT 10
       COUNT_LT 20
   evaluates to:
       (COUNT = 1) OR (COUNT > 10  AND COUNT < 20)
   and will cause the command list that follows it to be executed if
   the counter is equal to one, or is between 10 and 20.
   10.1  Condition Command Format
        Condition  commands  start  with  the  standard   four-octet
   command  header.   The high-order bit of the command type byte is
   used as a negate flag:  if this bit is set, the boolean value  of
   the  condition  is  negated.   This flag applies to one condition
   only, and not to other conditions in the condition list.
   Page 100
   LDP Specification                            Conditional Commands
                0             0 0   1         1
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
               +---------------+---------------+
             0 |        Command Length         |
               +---------------+---------------+
             1 | CONDITION     |N|    Type     |
               +---------------+---------------+
                       Condition Command Header
                               Figure 66
   10.2  COUNT Conditions
        The COUNT conditions (COUNT_EQ, COUNT_GT and  COUNT_LT)  are
   used to compare the breakpoint counter to a specified value.  The
   counter is set to zero when the breakpoint  is  STARTed,  and  is
   incremented  by  the INC_COUNT breakpoint command.  The format is
   the same for the COUNT_EQ, COUNT_GT and COUNT_LT conditions.
                0             0 0   1         1
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
               +---------------+---------------+
             0 |               8               |
               +---------------+---------------+
             1 | CONDITION     |N|  Type       |
               +---------------+---------------+
             2 |                               |
               +--          Value            --+
             3 |                               |
               +---------------+---------------+
                        COUNT Condition Format
                               Figure 67
   COUNT_* Condition FIELDS:
                                                            Page 101
   RFC-909                                                 July 1984
   Type
        One of COUNT_EQ, COUNT_LT and COUNT_GT.   The  condition  is
        TRUE  if  the  breakpoint  counter  is  [EQ  |  LT | GT] the
        specified value.
   Value
        A 32-bit value to be compared to the counter.
   10.3  CHANGED Condition
        The CHANGED  condition  is  TRUE  if  the  contents  of  the
   specified   location  have  changed  since  the  last  time  this
   breakpoint occurred.  Only one location may be specified  as  the
   object   of  CHANGED  conditions  per  breakpoint.   The  CHANGED
   condition is always FALSE the first time the breakpoint occurs.
                0             0 0   1         1
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
               +---------------+---------------+
             0 |              14               |
               +---------------+---------------+
             1 | CONDITION     |N|  CHANGED    |
               +---------------+---------------+
             2 |                               |
               +--                           --+
             3 |            Address            |
               +--                           --+
             4 |                               |
               +--                           --+
             5 |                               |
               +--                           --+
             6 |                               |
               +---------------+---------------+
                           CHANGED Condition
                               Figure 68
   Page 102
   LDP Specification                            Conditional Commands
   CHANGED FIELDS:
   Address
        The full 5-word address of the location to be tested by  the
        CHANGED command.
   10.4  COMPARE Condition
        The COMPARE condition compares two locations using  a  mask.
   The condition is TRUE if (<loc1> & <mask>) = (<loc2> & <mask>).
                                                            Page 103
   RFC-909                                                 July 1984
                0             0 0   1         1
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
               +---------------+---------------+
             0 |              28               |
               +---------------+---------------+
             1 | CONDITION     |N|  COMPARE    |
               +---------------+---------------+
             2 |                               |
               +--                           --+
             3 |            Address 1          |
               +--                           --+
             4 |                               |
               +--                           --+
             5 |                               |
               +--                           --+
             6 |                               |
               +---------------+---------------+
             7 |                               |
               +--          Mask             --+
             8 |                               |
               +-------------------------------+
             9 |                               |
               +--                           --+
             10|            Address 2          |
               +--                           --+
             11|                               |
               +--                           --+
             12|                               |
               +--                           --+
             13|                               |
               +-------------------------------+
                           COMPARE Condition
                               Figure 69
   Page 104
   LDP Specification                            Conditional Commands
   COMPARE FIELDS:
   Address 1
   Address 2
        The 5-word addresses of the locations to be compared.
   Mask
        A 32-bit mask specifying which bits in the locations  should
        be compared.
   10.5  TEST Condition
        The TEST condition is used to compare a location to a value,
   using  a  mask.   The  condition  is  TRUE  if (<loc> & <mask>) =
   <value>.
                                                            Page 105
   RFC-909                                                 July 1984
                0             0 0   1         1
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
               +---------------+---------------+
             0 |              22               |
               +---------------+---------------+
             1 | CONDITION     |N|  TEST       |
               +---------------+---------------+
             2 |                               |
               +--                           --+
             3 |            Address            |
               +--                           --+
             4 |                               |
               +--                           --+
             5 |                               |
               +--                           --+
             6 |                               |
               +---------------+---------------+
             7 |                               |
               +--          Mask             --+
             8 |                               |
               +-------------------------------+
             9 |                               |
               +--          Value            --+
             10|                               |
               +-------------------------------+
                            TEST Condition
                               Figure 70
   TEST FIELDS:
   Address
        The 5-word address of the location to  be  compared  to  the
        value.
   Mask
        A 32-bit mask specifying which bits in the  location  should
        be compared.
   Value
        A 32-bit value to compare to the masked location.
   Page 106
   LDP Specification                            Conditional Commands
                                                            Page 107
   RFC-909                                                 July 1984
   Page 108
   LDP Specification                             Breakpoint Commands
                              CHAPTER 11
                          Breakpoint Commands
        Breakpoint commands are used to set the value of  breakpoint
   variables.   These commands are only valid within breakpoints and
   watchpoints.  They are sent from the host to the target  as  data
   in  BREAKPOINT_DATA  commands.   Figure  71 contains a summary of
   breakpoint commands:
    Command                  Description
   ------------------------+-------------------------------------
   INCREMENT <location>      Increment the specified location
   INC_COUNT                 Increment the breakpoint counter
   OR                        OR two breakpoint condition lists
   SET_PTR <n> <location>    Set pointer <n> to the contents of
                             <location>
   SET_STATE <n>             Set the breakpoint state variable
                             to <n>
                      Breakpoint Command Summary
                               Figure 71
   11.1  INCREMENT Command
        The INCREMENT command increments the contents of a specified
   location.  The location may be in any address space writable from
   LDP.
                                                            Page 109
   RFC-909                                                 July 1984
                0             0 0   1         1
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
               +---------------+---------------+
             0 |               14              |
               +---------------+---------------+
             1 | BREAKPOINT    |  INCREMENT    |
               +---------------+---------------+
             2 |                               |
               +--                           --+
             3 |            Address            |
               +--                           --+
             4 |                               |
               +--                           --+
             5 |                               |
               +--                           --+
             6 |                               |
               +---------------+---------------+
                       INCREMENT Command Format
                               Figure 72
   INCREMENT FIELDS:
   Address
        The full address of the location whose contents  are  to  be
        incremented.
   11.2  INC_COUNT Command
        The INC_COUNT command  increments  the  breakpoint  counter.
   There  is  one  counter  variable  for  each   breakpoint.  It is
   initialized to zero when the breakpoint is created,  when  it  is
   armed  with  the START command, and whenever the breakpoint state
   changes.  The counter is tested by the COUNT_* conditions.
   Page 110
   LDP Specification                             Breakpoint Commands
                0             0 0   1         1
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
               +---------------+---------------+
             0 |               4               |
               +---------------+---------------+
             1 | BREAKPOINT    |  INC_COUNT    |
               +---------------+---------------+
                       INC_COUNT Command Format
                               Figure 73
   11.3  OR Command
        The OR command delineates  two  and_lists  in  a  breakpoint
   condition  list.   A  condition  list  is  TRUE  if any of the OR
   separated and_lists in it are TRUE.  A breakpoint condition  list
   may  contain  zero,  one  or,  many  OR commands.  See 'Condition
   Commands' for an explanation of condition lists.
                0             0 0   1         1
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
               +---------------+---------------+
             0 |               4               |
               +---------------+---------------+
             1 | BREAKPOINT    |      OR       |
               +---------------+---------------+
                           OR Command Format
                               Figure 74
                                                            Page 111
   RFC-909                                                 July 1984
   11.4  SET_PTR Command
        The SET_PTR command loads the specified  breakpoint  pointer
   with  the  contents of a location.  The pointer variables and the
   SET_PTR command are intended to provide a primitive but unlimited
   indirect    addressing   capability.    Two   addressing   modes,
   BPT_PTR_OFFSET and BPT_PTR_INDIRECT, are used for referencing the
   breakpoint  pointers.   For example, to follow a linked list, use
   SET_PTR to load a pointer with the start of the  list,  then  use
   successive  SET_PTR  commands with addressing mode BPT_PTR_OFFSET
   to get successive elements.
                0             0 0   1         1
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
               +---------------+---------------+
             0 |               16              |
               +---------------+---------------+
             1 | BREAKPOINT    |  SET_PTR      |
               +---------------+---------------+
             2 |            Pointer            |
               +---------------+---------------+
             3 |                               |
               +--                           --+
             4 |            Address            |
               +--                           --+
             5 |                               |
               +--                           --+
             6 |                               |
               +--                           --+
             7 |                               |
               +---------------+---------------+
                        SET_PTR Command Format
                               Figure 75
   SET_PTR FIELDS:
   Pointer
        The pointer to be changed.  Allowable values are 0 and 1.
   Address
   Page 112
   LDP Specification                             Breakpoint Commands
        The full address of the location whose contents  are  to  be
        loaded into the given pointer variable.
   11.5  SET_STATE Command
        The SET_STATE command sets the breakpoint state variable  to
   the  specified  value.   This  is  the  only method of changing a
   breakpoint's state from within  a  breakpoint.  The  breakpoint's
   state  may  be  also be changed by a START command from the host.
   The state variable is initialized to zero when the breakpoint  is
   created.
                0             0 0   1         1
                0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
               +---------------+---------------+
             0 |               6               |
               +---------------+---------------+
             1 | BREAKPOINT    |  SET_STATE    |
               +---------------+---------------+
             2 |         State Value           |
               +-------------------------------+
                       SET_STATE Command Format
                               Figure 76
   SET_STATE FIELDS:
   State Value
        The new value for the breakpoint state variable.   Must  not
        be  greater  than  the  maximum state value specified in the
        CREATE BREAKPOINT command that created this breakpoint.
                                                            Page 113
   RFC-909                                                 July 1984
   Page 114
   LDP Specification                             Diagram Conventions
                              APPENDIX A
                          Diagram Conventions
        Command and message diagrams are used in  this  document  to
   illustrate  the  format  of these entities.   Words are listed in
   order of transmission down the page.   The  first  word  is  word
   zero.   Bits within a word run left to right, most significant to
   least.   However,   following  a  convention  observed  in  other
   protocol  documents,  bits are numbered in order of transmission;
   the most significant bit in a word is transmitted first.  The bit
   labelled '0' is the most significant bit.
                     0             0 0   1         1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +---------------+---------------+
                  0 |M|                           |L|
                    +---------------+---------------+
                  1 | Most Sig Octet| Least S. Octet|
                    +---------------+---------------+
                    M = most significant bit in word zero,
                        transmitted first
                    L = least significant bit in word zero,
                        transmitted last
                            Sample Diagram
                               Figure 77
                                                            Page 115
   RFC-909                                                 July 1984
   Page 116
   LDP Specification                                 Command Summary
                              APPENDIX B
                            Command Summary
        The following table lists all non-breakpoint LDP commands in
   alphabetical order, with a brief description of each.
                                                            Page 117
   RFC-909                                                 July 1984
                          Sender
   Command            | Host Target | Function
   -------------------+-------------+---------------------------
   ABORT                 X            Abort outstanding commands
   ABORT_DONE                  X      Acknowledge ABORT
   ADDRESS_LIST                X      Return valid address ranges
   BREAKPOINT_DATA       X            Send breakpoint commands
   BREAKPOINT_LIST             X      Return list of breakpoints
   CONTINUE              X            Resume execution
   CREATE                X            Create target object
   CREATE_DONE                 X      Acknowledge CREATE
   DELETE                X            Delete target object
   DELETE_DONE                 X      Acknowledge DELETE
   EXCEPTION                   X      Report target exception
   ERROR                       X      Report error with a host command
   ERRACK                X            Acknowledge ERROR
   GET_OBJECT            X            Get object descriptor from name
   GET_PHYS_ADDRESS      X            Get address in physical form
   GOT_OBJECT                  X      Return object descriptor
   GOT_PHYS_ADDRESS            X      Return physical address
   HELLO                 X            Initiate LDP session
   HELLO_REPLY                 X      Return LDP parameters
   LIST_ADDRESSES        X            Request valid address ranges
   LIST_BREAKPOINTS      X            Request breakpoint list
   LIST_NAMES            X            Request name list
   LIST_PROCESSES        X            Request process list
   MOVE                  X            Read data from target
   MOVE_DONE                   X      Acknowledge MOVE completion
   MOVE_DATA                   X      Send data request by MOVE
   NAME_LIST                   X      Return name list
   PROCESS_LIST                X      Return process list
   READ                  X            Read data from target
   READ_DATA                   X      Return data requested by READ
   READ_DONE                   X      Acknowledge READ completion
   REPEAT_DATA           X            Write copies of data
   REPORT                X            Request status of object
   START                 X            Start target object
   STATUS                      X      Return status of object
   STEP                  X            Step execution of target object
   STOP                  X            Stop target object
   SYNCH                 X            Check sequence number
   SYNCH_REPLY                 X      Confirm sequence number
   WRITE                 X            Write data
   WRITE_MASK            X            Write data with mask
   Page 118
   LDP Specification                                 Command Summary
                            Command Summary
                               Figure 78
                                                            Page 119
   RFC-909                                                 July 1984
   Page 120
   LDP Specification                 Commands, Responses and Replies
                              APPENDIX C
                    Commands, Responses and Replies
        The following table shows the relationship between commands,
   responses  and  replies.   Commands are sent from the host to the
   target.  Some commands elicit responses and/or replies  from  the
   target.   Responses  and  replies are sent from the target to the
   host.  The distinction between them is that the target sends only
   one  reply  to  a  command,  but  may  send  multiple  responses.
   Responses always contain data, whereas replies may or may not.
                                                            Page 121
   RFC-909                                                 July 1984
        Command            | Response     | Reply
        -------------------+--------------+------------------
        ABORT                               ABORT_DONE
        BREAKPOINT_DATA
        CONTINUE
        CREATE                              CREATE_DONE
        DELETE                              DELETE_DONE
        GET_OBJECT                          GOT_OBJECT
        GET_PHYS_ADDRESS                    GOT_PHYS_ADDRESS
        HELLO                               HELLO_REPLY
        LIST_ADDRESSES                      ADDRESS_LIST
        LIST_BREAKPOINTS                    BREAKPOINT_LIST
        LIST_NAMES                          NAME_LIST
        LIST_PROCESSES                      PROCESS_LIST
        MOVE               MOVE_DATA        MOVE_DONE
        READ               READ_DATA        READ_DONE
        REPEAT_DATA
        REPORT                              STATUS
        START
        STEP
        STOP
        SYNCH                               SYNCH_REPLY
        WRITE
        WRITE_MASK
                    Commands, Responses and Replies
                               Figure 79
   Page 122
   LDP Specification                                        Glossary
                              APPENDIX D
                               Glossary
   FSM
        Finite  state  machine.   Commands  of  each  breakpoint  or
        watchpoint   are  implemented  as  part  of  a  finite state
        machine.  A list of breakpoint commands is  associated  with
        each state.  There are several breakpoint commands to change
        from one state to another.
   host
        The 'host' in an LDP session is the  timesharing  system  on
        which the user process runs.
   long
        A long is a 32-bit quantity.
   octet
        An octet is an eight-bit quantity.
   RDP
        The  Reliable  Data  Protocol  (RDP) is  a  transport  layer
        protocol designed as a low-overhead alternative to TCP.  RDP
        is a connection oriented protocol  that  provides  reliable,
        sequenced message delivery.
   server process
        The LDP server process is the passive participant in an  LDP
        session.   The  server  process  usually resides on a target
        machine such as a PAD, PSN or gateway.  The  server  process
        waits for a user process to initiate a session, and responds
        to commands from the user  process.   In  response  to  user
        commands, the server may perform services on the target like
        reading and writing memory locations or setting breakpoints.
        'Server'  is  sometimes  employed as a shorthand for 'server
        process'.
                                                            Page 123
   RFC-909                                                 July 1984
   target
        The 'target' in an LDP session is the PSN,  PAD  or  gateway
        that  is  being  loaded,  dumped  or  debugged  by the host.
        Normally, LDP will be implemented in the target as a  server
        process.     However,   in   some   targets   with   strange
        requirements, notably the Butterfly, the target LDP may be a
        user process.
   user process
        The LDP user process is the active  participant  in  an  LDP
        session.   The  user  process  initiates  and terminates the
        session and sends commands  to  the  server  process   which
        control  the session.  The user process usually resides on a
        timesharing host and is  driven  by  a  higher-level  entity
        (e.g., an application program like an interactive debugger).
        'User' is  sometimes  employed  as  a  shorthand  for  'user
        process'.
   word
        A word is a sixteen-bit quantity.
   Page 124
                                 INDEX
   ABORT command............................................ 35
   ABORT_DONE reply......................................... 36
   address.............................................. 60, 66
   address descriptor....................................... 20
   address format................................... 19, 25, 31
   address ID............................................... 22
   address mode......................................... 20, 22
   address mode argument.................................... 21
   address offset........................................... 20
   addressing............................................... 19
   ADDRESS_LIST reply................................... 76, 77
   BASIC_DEBUGGER....................................... 12, 32
   breakpoint... 9, 13, 57, 60, 71, 79, 92, 93, 95, 96, 99, 107
   breakpoint commands.......................... 9, 94, 95, 107
   breakpoint counter........................ 94, 100, 101, 110
   breakpoint data...................................... 97, 99
   breakpoint state variable........................... 94, 107
   breakpoint variables..................................... 94
   BREAKPOINT_DATA command..................... 73, 94, 95, 107
   BREAKPOINT_LIST reply................................ 79, 80
   CHANGED condition....................................... 102
   command class............................................ 16
   command length field..................................... 16
   COMPARE Condition....................................... 103
   condition command header................................ 101
   conditional commands................................. 94, 99
   CONTINUE command......................................... 62
   control commands...................................... 9, 57
   COUNT condition.................................... 110, 111
   COUNT_EQ condition...................................... 101
   COUNT_GT condition...................................... 101
   COUNT_LT condition...................................... 101
   CREATE command............................... 69, 70, 73, 75
   create types............................................. 70
   CREATE_DONE reply.................................... 73, 75
   data octets...................................... 43, 47, 52
   data packing............................................. 10
   data transfer commands................................ 9, 41
   data transmission........................................ 10
   datagrams................................................. 5
   debugging.............................................. 1, 3
                                                            Page 125
   default breakpoint................................... 71, 92
   DELETE command....................................... 73, 75
   DELETE_DONE reply........................................ 75
   descriptor........... 20, 57, 61, 62, 63, 64, 65, 73, 75, 93
   dumping................................................... 3
   ERRACK............................................... 10, 39
   ERROR codes.............................................. 38
   ERROR reply.......................................... 37, 67
   EXCEPTION trap........................................... 66
   finite state machine................................. 60, 93
   FSM breakpoint................................... 71, 92, 94
   FULL-DEBUGGER............................................ 12
   FULL_DEBUGGER............................................ 32
   gateway................................................ 3, 9
   GET_OBJECT command................................... 89, 91
   GET_PHYS_ADDR command................................ 87, 88
   GOT_OBJECT reply..................................... 89, 91
   GOT_PHYS_ADDR reply.................................. 87, 88
   HELLO command......................................... 9, 29
   HELLO_REPLY....................................... 9, 19, 30
   host descriptor.......................................... 41
   implementation....................................... 12, 31
   INC_COUNT command......................... 94, 107, 110, 111
   INCREMENT command....................................... 109
   internet.................................................. 5
   internet protocols........................................ 4
   IP........................................................ 5
   LDP command formats...................................... 15
   LDP header........................................... 15, 16
   LDP Version.............................................. 30
   LIST commands............................................ 73
   LIST_ADDRESSES command............................... 76, 77
   LIST_BREAKPOINTS command............................. 79, 80
   LIST_NAMES command................................... 84, 85
   LIST_PROCESSES command................................... 82
   LOADER_DUMPER........................................ 12, 32
   loading................................................ 1, 3
   long address format...................................... 20
   management commands...................................... 67
   memory object............................................ 73
   MOVE command................................. 22, 41, 47, 49
   MOVE sequence number..................................... 52
   MOVE_DATA response................................... 22, 51
   MOVE_DONE reply.......................................... 52
   NAME_LIST reply...................................... 84, 85
   offset............................................... 20, 22
   OR command.............................................. 111
   Page 126
   PAD.................................................... 3, 9
   pattern.................................................. 54
   PHYS_ADDRESS............................................. 57
   PHYS_MACRO............................................... 60
   PROCESS.................................................. 57
   PROCESS_CODE............................................. 60
   PROCESS_LIST reply....................................... 82
   protocol commands......................................... 9
   PSN.................................................... 3, 9
   RDP................................................... 5, 15
   READ command..................................... 41, 43, 44
   READ sequence number..................................... 47
   READ_DATA response................................... 45, 46
   READ_DONE reply.......................................... 47
   repeat count............................................. 54
   REPEAT_DATA command.................................. 41, 53
   REPORT command................................... 63, 64, 94
   sequence number...................................... 10, 39
   session................................................... 9
   SET_PTR command................................ 94, 111, 112
   SET_STATE command.............................. 94, 107, 113
   short address format..................................... 25
   START command........................................ 59, 60
   STATUS reply..................................... 64, 65, 94
   STEP command......................................... 62, 63
   STOP command......................................... 60, 61
   SYNCH.................................................... 10
   SYNCH command............................................ 33
   SYNCH_REPLY.............................................. 34
   system type.............................................. 30
   target start address......................... 43, 44, 46, 54
   transport................................................. 9
   watchpoint.......... 13, 57, 60, 71, 92, 93, 95, 96, 99, 107
   WRITE command........................................ 41, 42
   WRITE_MASK command....................................... 56
                                                            Page 127
   Page 128
/data/webs/external/dokuwiki/data/pages/rfc/rfc909.txt · Last modified: 1992/09/23 19:37 (external edit)