From burke@vxdesy.desy.de Mon Feb  1 19:08:09 1993
Newsgroups: comp.sys.acorn.tech
From: burke@vxdesy.desy.de (Stephen Burke)
Subject: Throwback protocol (client end)
Organization: (DESY, Hamburg, Germany)
Date: Sun, 31 Jan 1993 16:40:05 GMT

Nobody else has posted this, so here goes. To use throwback (as a client) you
need the DDEUtils module, an editor which supports throwback, and (AFAIK) any
version of RISC OS. There are three SWIs:

DDEUtils_ThrowbackStart (&42587)

Entry: Don't Care

Exit: All registers preserved

Function: Start a throwback session


DDEUtils_ThrowbackSend (&42588) (The documentation actually calls this SWI
                                 Throwback_Send, but I think it's a mistake).

Entry: R0 = reason code
       R2-R5 variable

       R0 = 0 (Throwback_ReasonProcessing)
       R2 = pointer to full pathname of file (null terminated)

       R0 = 1 (Throwback_ReasonErrorDetails)
       R2 = pointer to full pathname of file (null terminated)
       R3 = error line number
       R4 = severity:
          = 0 for warning
          = 1 for error
          = 2 for serious error
       R5 = pointer to error description string (null terminated)

       R0 = 2 (Throwback_ReasonInfoDetails)
       R2 = pointer to full pathname of file (null terminated)
       R3 = line number to which info message refers
       R4 = 0
       R5 = pointer to informational message (null terminated)

Exit: R0-R4 preserved

Function: Call once with reason code 0, and then with code 1 or 2 for
          each error/message


DDEUtils_ThrowbackEnd (&42589)

Entry: Don't Care

Exit: All registers preserved

Function: End a throwback session


All three SWIs can give errors of "No task registered for throwback" and
"Throwback not available outside the desktop" (no error numbers given).

That's it; simple really :-)

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