abcprintd protocol

FF 00	-> end of print job

FF FF	-> FF as part of print job

All other bytes are part of a print job


File sharing commands:
----------------------

All commands start with FF <opcode> <seq>, and all responses begin
with FF <opcode> <seq> <err>, where <err> is 0 for OK and otherwise
0x80+ABC80 error code.

FF A0 ss ixix NNNNNNNNEEE	OPEN TEXT

   	ixix = Address of IX-map (used as a handle)

	Open an existing file for reading in text mode
	If the filename is empty (all spaces), read the directory

FF A1 ss ixix NNNNNNNNEEE	OPEN BINARY

	Open an existing file for reading in binary (block) mode

FF A2 ss ixix NNNNNNNNEEE	PREPARE TEXT

   	Create a new file for writing in text mode

FF A3 ss ixix NNNNNNNNEEE	PREPARE BINARY

   	Create a new file for writing in binary (block) mode

FF A4 ss ixix			INPUT

   	Read a text line; response followed by len (2 bytes) + data

FF A5 ss ixix len		READ BLOCK

	Read a data block of specified len; response: len + data

FF A6 ss ixix len data...	PRINT

   	Write a text line or data block

FF A7 ss ixix			CLOSE

   	Close a file handle

FF A8 ss xxxx			CLOSE ALL

	All files are closed and forgotten.  xxxx ignored.

FF A9 ss xxxx			CLOSE ALL NO REPLY

	All files are closed and forgotten.  xxxx ignored.
	No response token is sent.


Debug console
-------------

FF C0 .... 00

	Text between FF C0 and terminating 00 are written out on
	stdout for abcprintd if the -c option was given.  Intended to
	be used for debugging messages.