byte

ASYNC(3)						     Library Functions Manual							  ASYNC(3)

NAME

       async - framing for a serial line to Datakit

SYNOPSIS

       ctlfd = open(".../ctl", ORDWR);
       write(ctlfd, "push async", 10);

DESCRIPTION

       This is not a device, but rather a stream module (see stream(3)) that can be pushed onto a stream.  This module provides the framing neces-
       sary to treat a serial line as a Datakit trunk.	It is usually pushed onto a stream before the dkmux module.  The  frame  includes  a  CRC.
       Any received frames with an incorrect CRC are discarded.

       The format of a message upstream of the module is:

	      channel # low byte
	      channel # high byte
	      control byte (0 means none)
	      data bytes

       The format of a frame is:

	      0x7d
	      0x7d
	      channel # low byte
	      channel # high byte
	      crc low byte
	      crc high byte
	      0x7d
	      0x7d

       All control bytes in the frame are preceded by a 0x9d byte.  All 0x9d and 0x7d bytes in the data are followed by a 0x00 byte to distinguish
       them from framing or control specifiers.

SEE ALSO

       stream(3), cons(3), dk(3)

SOURCE

       /sys/src/9/port/stasync.c

																	  ASYNC(3)