Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!texsun!texsun.central-relay.sun.com!convex!trsvax!authorplaceholder
From: uhclem@trsvax.UUCP
Newsgroups: comp.unix.xenix
Subject: Re: tty error]
Message-ID: <196500012@trsvax>
Date: 1 Apr 88 14:49:00 GMT
References: <884@udccvax1.acs.udel.EDU>
Lines: 56
Nf-ID: #R:udccvax1.acs.udel.EDU:-88400:trsvax:196500012:000:2497
Nf-From: trsvax.UUCP!uhclem    Apr  1 09:49:00 1988


<>
Base notes wants help on message:

B>       init:/dev/ttyx05: getty keeps dying. There may be a problem 

As one of the responses has noted, this message may have come from
init for having to spin-off too many gettys in a short time.

If this is a real IBM AT serial/parallel adapter or one that is an exact
clone (used same RS232-C line receivers) then this information may assist.

The line driver IBM used the 75154 line receiver which is sensitive
to noise, more so than the 1489 which more systems use for RS232-C line
receivers.

Anyway, we found if you had an IBM AT adapter in your machine and
a non-ribbon cable (6ft) other than IBM's connected and it was not
connected to anything, if you enabled the line, the earlier releases
of XENIX-286 would bog down or die after a while.   The above message appears
to part of a way of keeping that from happening in the new releases.
It does come from /etc/init.   We did something similar in one of our
own XENIX releases.

What causes it?  We found that when the line was enabled, the CD line
would be floating high enough to cause a getty to be started.  The
banner would be transmitted and these transitions would cause the
CD line to swing low and high, very minute, but enough to generate
8 to 10 interrupts per character requesting the getty by killed and
another started.  The real, sold by big-blue IBM serial cable is
shielded and does not exhibit this problem unless you extend it with
a lot of unshielded stuff.   Perhaps a better word for the message
might have been "thrashing".

We also found that ribbon cable did not seem to have this problem - apparently
enough distance between 8 and 2/3 to reduce induction.  Adapter cards
from other vendors we tried all used 1489's and did not display this
problem.

The moral of all this was not to enable a line that did not have a computer,
modem or terminal attached.  

Hope that helps.

<This information is provided by an individual and is not nor should be
 construed  as  being  provided  by  Radio  Shack or Tandy Corp.  Radio
 Shack/Tandy Corp has no obligation to support the information provided
 in  any way.  Over half of the hydrocarbon pollution in Tarrant county
 comes from the northern third of the county which is in the country.
 What's doing it?   Cows burping.   How do you fit a smog device on that?>
						
						"Thank you, Uh Clem."
						Frank Durda IV
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