Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!natinst!bigtex!james
From: james@bigtex.cactus.org (James Van Artsdalen)
Newsgroups: comp.unix.sysv386
Subject: Re: Ethernet Cards
Message-ID: <50695@bigtex.cactus.org>
Date: 5 Dec 90 02:57:40 GMT
References: <707@denwa.uucp> <200@bigfoot.first.gmd.de>
Reply-To: james@bigtex.cactus.org (James Van Artsdalen)
Organization: Institute of Applied Cosmology, Austin TX
Lines: 47

In <200@bigfoot.first.gmd.de>, tmh@bigfoot.FOKUS.GMD.DBP.DE (Thomas Hoberg)
	wrote:

> I am all confused! I remember to have read that with the AT bus
> design a 16-bit peripheral will automatically use up 128k of memory
> space (something to do with the signals available on the connector).

This is correct.  Any memory on the AT bus that is 16 bits wide
occupies the entire 128K area it's in.

There are two sets of addresses: LA<17:23> and SA<0:19>. LAs are
valid when BALE is high.  SAs are valid on the trailing edge of BALE.

The problem is that in order to tell the system that it's a 16 bit
cycle, you have to drive MEMCS16 quickly, before waiting for the
trailing edge of BALE.  So you must use LA<17:23>, which only has
granularity to 128K.  Bummer.

> This is probably not true for peripherals in the I/O space (disk
> controllers and the like)

Right.

> and I can't really believe it's true for LIM 3.2 type memory boards
> (such as the first Intel Above Board), that use a single 64k window.

Not right.  The AT memory controller doesn't know what's out there.
The rules are the same for everyone: if it's memory, and it's 16 bit,
it's 128K wide.

> However I recently experienced trouble with a VGA board that was
> jumpered for 16-bit ROM access, thus over- laying our Adaptec's ROM
> area. Rejumpering for 8-bit access solved the problem [...]

This is a very common problem.  If you have a 16 bit video ROM at
C000:0, you can't have a hard disk controller with 8 bit ROM at
C800:0 or even D800:0.

On the other hand, it might be possible to get away with an 8 bit VGA
ROM and a 16 bit w/RAM network card.  If your system shadows the VGA
ROM before the network card is turned on, then there might never be a
time when there is a conflict.  Same thing for unix - unix will never
use the VGA ROM again, so once the network card is turned on and bent
on messing up the VGA, you'll be safe.
-- 
James R. Van Artsdalen          james@bigtex.cactus.org   "Live Free or Die"
Dell Computer Co    9505 Arboretum Blvd Austin TX 78759         512-338-8789