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Date: Sun, 23 Jun 1996 05:12:54 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199606221912.FAA09329@godzilla.zeta.org.au>
To: FreeBSD-hackers@freebsd.org, revr@cadre.nl, wilko@yedi.iaf.nl
Subject: Re: HELP: serial port grief on Asus P55TP4N
Sender: owner-hackers@freebsd.org
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>I'm sending this to -hackers on behalf of a friend of mine who has 
>just converted to FreeBSD 2.1R. His system is a P100 on a Asus
>P55TP4N with 32Mb, SC200 and ATI Mach64 VGA.

>He has all sorts of problems when using the internal serial ports
>of the Asus in combination with UUCP. It's really weird... :-(

>The uucp config files are identical to mine (I have a P55TP4XE).

>Symptoms:

>- when X was running -> console messages 'tty level buffer overflow'
>- without X -> errors logged by uucp 'uucp checksum failed'
>- he also tried ijppp and that seems to work OK... (???)

Uucp checksum errors are known to be caused by bugs in the UMC i/o
chip which is found in some ASUS motherboards (e.g. the P55TP4XE
rev.2.4).  The UARTs lose sync when their speed is set while data
is arriving, and uucp sets the speed a lot as a side affect of doing
tcsetattr()'s (it doesn't change the speed but it I think it toggles
state bit(s)).  This can be worked around in most cases by changing
the driver to skip setting the speed if the speed hasn't changed.

Bruce