RFC 186 (rfc186) - Page 2 of 17
Network graphics loader
Alternative Format: Original Text Document
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