Re: ALM-2 under SunOS4.1.1 on a 3/160-type machine? (SUMMARY)

From: Bob Cunningham (
Date: Mon Feb 11 1991 - 15:12:37 CST

Thanks to many (esp. Hal Stern). The essential checklist is:

(a) have you checked /etc/ttytab to make sure the ttyh* devices are
        turned on, have gettys running, and have "local" set correctly
        so that they will ignore the h/w carrier detect?
(b) do you have the mcp* devices configured into the kernel?
(c) do /dev/ttyh* exist?
(d) make sure you understand what ttysoftcar(8) is doing!

As it turns out, I had to do one extra little bit of "magic", rm'ing
/dev/mcp* and /dev/ttyh* and re-running

        /dev/MAKEDEV mcp0

in order to actually get things running after a kernal rebuild (which
shouldn't have been necessary, I still don't understand why the rest
of this wouldn't work right until after I did that).

The important part, however, not just for ALM-2 (aka MCP) boards, but
for ALL serial lines, is to understand something about how ttysoftcar(8)
works. I'm still not sure I do, but here's what I think I know:

In general under SunOS4.1.1 it's not necessary to fiddle with kernal
rebuilds or even eeprom settings in order to turn on or turn off
carrier detect. What IS necessary is to properly declare the ports
in /etc/ttytab. If "local" is there, software carrier detection
is turned ON (and hardware carrier detection disabled). If the
entry reads anything else, software carrier detection is turned
OFF, all of that via "/usr/etc/ttysoftcar -a > /dev/null 2>&1"
command in /etc/rc.local.

If the device is not listed in /etc/ttytab, apparently it defaults
to the flags value in the kernal configuration and/or eeprom setup.

Having said all of that, I should also add that--under some conditions
still not completely clear to me--ttysoftcar may not always work.
In particular, in using it directly (e.g., ttysoftcar [-y|-n] /dev/ttymumble)
the command sometimes seems to hang. Also, having "remote" instead
of "local" does not always seem to keep software carrier detection
off. On several systems here with modems (e.g., on ttya), I've
found myself having to add:

/usr/etc/ttysoftcar -n /dev/ttya the end of /etc/rc.local in order to actually get hardware
carrier detect.

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