From owner-freebsd-alpha  Thu Oct 21 18:40:23 1999
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From: Terry Lambert <tlambert@primenet.com>
Message-Id: <199910220140.SAA05716@usr07.primenet.com>
Subject: Re: ata busmaster i/o port on alpha
To: gallatin@cs.duke.edu (Andrew Gallatin)
Date: Fri, 22 Oct 1999 01:40:08 +0000 (GMT)
Cc: sos@FreeBSD.ORG, freebsd-alpha@FreeBSD.ORG
In-Reply-To: <14348.40785.536064.278837@grasshopper.cs.duke.edu> from "Andrew Gallatin" at Oct 19, 99 01:02:14 pm
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> S=F8ren,
>=20
> I'm trying to get the on-board IDE controllers in some AlphaServer
> DS10 machines working well w/FreeBSD-current.  They use the Acer
> AladdinV IDE controller in combination with a FUJITSU MPD3108AT ATA-4
> disk.
>=20
> The problem is with where the "Bios" (aka the SRM console) puts the
> busmaster address:
>=20
> <12:45pm>opal/root:~#pciconf -r 'pci0:13:0' 0x20
> 0x00010111
>=20
> When you read the bus master address you mask off the upper 16 bits
> entirely and we see the address as 0x110 where as it should really be=20
> 0x10110.  When this happens, the disk is of course unusable.  After
> 5 retries, I see I/O errors when I try to access the disk.
>=20
> If I apply the following patch, DMA works:

[ ... ]

> So, my question:  Is are you loosing the upper 16 bits for a reason,
> or is it valid to look at the upper 16 bits on all platforms?

It's truly cool to see that there are people with more Alpha
knowledge than x86 knowledge who are FreeBSD junkies.  8-).

This masking is a bit of historical arcanum dating back to the
IBM PC AT.

On x86, the I/O address space wraps.  Some code depends on this
behaviour.

This masking should probably be done in a (platform changeable)
macro, in any case.

The reason for making it a macro is to allow the macro to be used
in the PnP case, when the (unwrapped) address space has been
exhausted.

A bigger address space may be a problem, if the ISA interface
only connects 16 bits (yes, some PC's do this!).


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.


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