RFC 186 (rfc186) - Page 2 of 17

Network graphics loader

RFC 186                A Network Graphics Loader            12 July 1971


   For each execution of the display program, the Graphics Loader sets
   the proper output mode (suppressing output to the cathode ray tube at
   the DGSD machine), initializes the WAR before execution and saves the
   final value of the WAR after execution.  Thus it is easy for the
   Graphics Loader to transmit to the user only the "visible output" of
   the display program.

DESCRIPTION OF REQUESTS FROM THE REMOTE USER PROGRAM

   Request are in the form of 36 bit words.  The first word of a request
   is interpreted as two 18 bit fields.  The left half contains a number
   identifying which of six operations is being requested.  The right
   half is either a mode or is ignored, depending on the requested
   operation.  (If the left half is not a valid operation number, an
   error message is sent and the next word is considered to begin a new
   request.)

   Depending upon the operation requested and upon the mode, one word of
   argument data may or may not be read.  This word is (also) treated as
   two 18 bit halves.  The interpretation of the halves depends on the
   operation.  In the description of individual operations, the left
   half will be called A1; the right half will be called A2 (standing
   for Arguments 1 and 2).

   Error checking of the arguments is performed next.  If an error
   condition is present, error information is sent to the user program
   at the originating site and the Graphics Loader prepares itself for
   the next command.  If no error condition is present, an acknowledging
   message is sent unless the Suppress Acknowledgement mode prevails.
   For certain requests, the operation is performed before the
   acknowledgement is transmitted.

   For those operations involving a transfer of display program
   information (either to or from the Graphics Loader), this transfer is
   done next, after the error checking of arguments has been performed
   and after an acknowledge message has been sent.

   This done, the Graphics Loader reads the next command.













Michener