term% cat index.txt 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)