*BSD News Article 18580


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From: bde@kralizec.zeta.org.au (Bruce Evans)
Newsgroups: comp.os.386bsd.questions
Subject: Re: sio - problem with login hanging up
Date: 17 Jul 1993 00:41:03 +1000
Organization: Kralizec Dialup Unix Sydney: +61-2-837-1183 V.32bis
Lines: 26
Message-ID: <226elvINNt54@kralizec.zeta.org.au>
References: <g89r4222.742299445@kudu> <CA0ssD.1r2@sugar.NeoSoft.COM> <1993Jul12.075230.13102@cnplss5.cnps.philips.nl> <CA2HDw.FDp@sugar.NeoSoft.COM>
NNTP-Posting-Host: kralizec.zeta.org.au

In <CA2HDw.FDp@sugar.NeoSoft.COM> peter@NeoSoft.com (Peter da Silva) writes:

>> >SIO is pretty fascist about signals, apparently.

>SIO requires that you have all the right lines (DTR/DCD/etc) asserted before
>it'll work (I assume, all my cables carry all signals, and reported problems
>seem to be due to people with less complete ones). This isn't bad, it's just
>something you need to watch for.

Actually, it works with no special signals, at least talking to another sio,
provided the termio flags are set correctly (clocal -crtscts -hupcl).  By
a remarkable coincidence ;-) it starts up with the flags set correctly.
Unfortunately certain programs like to clobber the flags.  getty turns
clocal off and hupcl on (this is essential) so you need DCD connected or
wired high.  Dial-out programs don't need to change the flags.

There is a bug that causes infinite echoes talking to verbose modems.
The initial clocal setting allow open() to succeed when there is no
carrier.  getty clears clocal and enables echo.  Clearing clocal ought
to cause a fake hangup if there is no carrier, so that getty will start
again and block waiting for carrier.  The initial problem is easy to
work around using "stty -clocal </dev/sioNN" in /etc/rc.  However,
there may be problems later if a user sets clocal and hangs up, and
there may be problems with the dual bidirectional port.
-- 
Bruce Evans  bde@kralizec.zeta.org.au