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From: Terry Lambert <terry@lambert.org>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Problem using Serial Ports
Date: Mon, 26 Aug 1996 10:41:45 -0700
Organization: Me
Lines: 43
Message-ID: <3221E1D9.1C02DA5B@lambert.org>
References: <4vskqn$t95@prometheus.acsu.buffalo.edu>
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Patrick Leung wrote:
] Hi,
] I installed both Linux and FreeBSD recently. My serial
] ports work just fine with Linux, but not on FreeBSD. Each time
] FreeBSD tries to boot up my computer and detect the serial ports,
] my computer locks up and lots of dashed lines fly around on my
] screen. The only way I can get FreeBSD to boot the kernel all
] the way through to the login prompt is by disabling detection of
] my serial ports from the kernel config.
]
] I configured my kernel to use only the minumum number of drivers
] necessary:
] wd0 [harddrive], fd0 [floppy], sc0 [console].
] I have also tried FreeBSD on two of my friends computers, and
] got similar results. Does anyone know the cause of the problem
] and know the solution?
You are running an older version of FreeBSD and you have a MACH32
or MACH64 graphics interface.
The serial port probe for com4 (sio3) is writing to a register
that is normally reserved for use by com4.
What is happenening is that, due to an engineering screwup, the
com4 port address overlay is active when the mode that is supposed
to select it has not been invoked.
This is a bug in the MACH32/64 emulation of the IBM graphics
adapter standard which uses the com4 port range.
You should install a newer version of FreeBSD which does not
tickle the bug. Alternately, if you have a copy of the handbook
(if not, see the FAQ on www.freebsd.org), look up this problem.
The general fix for older versions of FreeBSD is to disable the
use of com4 in the /sys/i386/isa/sio.c file, and rebuild a kernel.
Terry Lambert
terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.