SSP_Commands


 A  number  of  commands  have  been  defined  that  all  the
 subsiduary SSPs must understand:

 -------------------------------------------------------------
 ASCII    Subroutine   Action may include:
 command  called
 -------------------------------------------------------------
 INIT     INITIALIZE   Initialize modules,crate etc
 STAR     START        Initialize counters etc.
 BSPI     BEGIN_SPILL  Initialize data buffer pointers etc.
 EVNT     EVENT        Read data from modules into data buffer
 ESPI     END_SPILL    Process data
 PAUS     PAUSE        None
 CONT     CONTINUE     None


 The  subroutines  called  on  each  command  (which  may  be
 dummies) are also listed.  The subroutines will typically be
 different for every subsiduary SSP, depending on  the  crate
 contents.




 Sending_a_command



                           CAUTION

     The use of SR and front-panel trigger  for  the  SSP
     described  below  makes the assumption that there is


     only one SSP in the system, and the host  is  acting
     as  the master.  In this case, the SSP asserts SR on
     the crate segment to interrupt the host.


 To send any of the above commands, the master must write the
 4  character  ASCII command word to the location $COMMAND in
 the SSP, followed by sending SSP GO to start the SSP.

 On receipt of SSP  GO,  the  SSPs  must  lower  SR  (service
 request).   After every command has been executed (except if
 SSP front panel trigger is enabled), the SSPs will raise  SR
 to  inform the master that they have finished, and halt.  In
 the case of front panel trigger being enabled, a  soft  halt
 is set, and SR is not raised.

 After the SSP has halted the master  must  read  the  return
 code  (see  $RET_CODE)  to  check  whether  the  routine has
 successfully executed.




 Soft_Halt


 The SSP is controlled by a Run bit in CSR 0 and  a  trigger.
 The  trigger may either come from a bit in CSR 0 or from the
 front panel input.  The SSP will start if the run bit is set
 and  a trigger occurs.  A normal HALT instruction will clear
 the run bit, which may only be set  again  via  FASTBUS.   A
 soft  halt instruction stops the SSP but the run bit remains
 set, so that a subsequent trigger will restart the SSP.

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