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RFC 0909

 
 
 

Loader Debugger Protocol

Part 2 of 4, p. 35 to 69
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prevText      Top       Page 35 
                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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          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.

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     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.

Top       Page 38 
                       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.

Top       Page 39 
                       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.

Top       Page 40 
                    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

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               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.

Top       Page 42 
                       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

Top       Page 43 
                                 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,

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     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

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     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.

Top       Page 46 
                       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

Top       Page 47 
          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.

Top       Page 48 
                       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

Top       Page 49 
          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.

Top       Page 50 
     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.

Top       Page 51 
                       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,

Top       Page 52 
          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.

Top       Page 53 
                       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

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          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.

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     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

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     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

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     the start and the end of the modification.

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                       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

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     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.

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                                 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.

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                       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.

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     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.

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     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.

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                       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.

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                       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.

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                       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

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          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

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          The address specifies the object the exception is for.

     Type

          The type of exception.  Values are target-dependent.

     Other Data

          Values are target-dependent.

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                                 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.


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