They often need too. The classic example is the Sparc, Mac, and PPC serial
ports. These interfaces support synchronous mode on a byte level needing
a very tty like interface
> line discipline could inform the low-level device driver what the
> "framing character" is, and this information would be used to determine
No framing character. Think instead
ioctl(tty_fd, TIOCSSYNC, &sync_defs);
v=TTY_LDISC_SYNCX25;
ioctl(tty_fd, TIOCLDISC, &v);
ioctl(tty_fd, SIOCGIFNAME, buf);
> stated above, synchronous devices will probably be always directly wired
> into the networking stack.
Not the low speed stuff. The tty layer is exactly what they need. I think
the framing is easy to handle too - just declare three of the error flags
for frame end, abort, and checksum byte (for the hardware computed HDLC
checksums off most chips).
Alan