From owner-freebsd-questions  Tue Oct 10 01:10:04 1995
Return-Path: owner-questions
Received: (from root@localhost)
          by freefall.freebsd.org (8.6.12/8.6.6) id BAA22007
          for questions-outgoing; Tue, 10 Oct 1995 01:10:04 -0700
Received: from godzilla.zeta.org.au (godzilla.zeta.org.au [203.2.228.34])
          by freefall.freebsd.org (8.6.12/8.6.6) with ESMTP id BAA21992
          ; Tue, 10 Oct 1995 01:09:50 -0700
Received: (from bde@localhost) by godzilla.zeta.org.au (8.6.9/8.6.9) id SAA11883; Tue, 10 Oct 1995 18:02:33 +1000
Date: Tue, 10 Oct 1995 18:02:33 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199510100802.SAA11883@godzilla.zeta.org.au>
To: itsymbal@husc.harvard.edu, msmith@atrad.adelaide.edu.au
Subject: Re: FreeBSD & ATI Mach64 install problem (follow-up)
Cc: hardware@freebsd.org, questions@freebsd.org
Sender: owner-questions@freebsd.org
Precedence: bulk

>> I have found that if I start with -c flag during boot and disable ALL com 
>> ports - sio0-3 then the card behaves appropriately. I do need to use a 
>> mouse ( at least) and preferably a modem. 

>It would appear that the Mach64 in your configuration conflicts with your
>serial ports.

Probably only sio3.

>> The ATI install disk claims the card is using Base I/O address 0x2ECh; 
>> however, with all com ports disabled it works fine if sc0 is set to either 
>> 0x2ec (card's setting) or 0x60.

>Leave sc0 at 0x60.  It's not trying to talk to the special registers on the
>Mach64.  

Setting it to 0x2EC is harmless because sc0 ignores the setting.  This
setting may even help by confusing the conflict checking code into
thinking that sc0 uses ports 0x2EC-0x2FB (actually only X uses it).
These addresses overlap with the normal ones for sio1 and sio3, and sc0
is probed first, so sio1 and sio3 may be skipped due to the conflict.

>> If I leave any one com port enabled, the card will mess up. Wether or not 
>> the particular com port is actually present does not seem to make a 
>> difference. 

>Are you certain about this?  0x2ec will conflict with sio3, which is at 0x2e8.
>I would expect this to cause some problems.  Note that most/all S3 based 
>video boards occupy this address, and thus conflict to some degree with
>com4.

sio does an outb(0x2EC, 0) if _any_ com port is enabled :-(.  It does
this to handle braindamage involving edge triggered interrupts (all
ports sharing an IRQ must have their IRQ enable disabled although it is
only possible to use one such port so it would be natural not to
configure the other ones).

Bruce