rfc909.txt

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     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






























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     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.





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     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.






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     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



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     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




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     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  |
                      +---------------+---------------+