Subject: Re: PWS 433a (Miata) question about SRM
To: Olaf Seibert <>
From: Jason Thorpe <>
List: port-alpha
Date: 11/20/1999 09:17:20
On Sat, 20 Nov 1999 15:41:49 +0100 
 Olaf Seibert <> wrote:

 > In the AlphaBIOS setup I selected the SRM for Digital Unix (that seemed
 > a better choice than SRM for OpenVMS). When I next powered down and up,
 > the SRM came up, but it told me there was an unsuppored card in slot 4,
 > and would I please remove it before it would do anything else.
 > The card in slot 4 was the video card (S3 864).

Earlier revisions of Miatas have a horrible core logic bug in them which
manifests itself when a device attempts to prefetch across a page boundary.
The SRM worked around this by refusing to enable cards that it didn't "know
about" which were plugged into the primary PCI bus.  These cards that it
"knew about" were known by SRM to not do the thing that caused the bug to

Plugging such devices into the secondary PCI bus (the 32-bit slots, which
are behind a PCI-PCI bridge, which prevents the bug from manifesting itself)
is allowed by SRM.

In the case of a video card, you're probably okay, since by default, that
card isn't going to be doing DMA.

However, if the card has a DMA engine on it for e.g. copying pixmaps from
host memory to display memory, there could be a problem when that DMA engine
is used.

I don't remember what card DEC generally OEM'd in those machines... I know
that AlphaServer 4100s often have S3 ... Trio64s maybe?  Or maybe 968s.

Anyhow, SRM is obviously allowing it to function, tho it probably didn't
set the Bus Master Enable bit in the PCI Command register on the card.

 > But my main question is: how can I use the SRM with the video card that
 > I have? It works well enough to show the countdown and the error
 > message,I don't see any reason why the SRM would have any trouble with
 > it. Besides, I obviously want to use the machine with wscons and X, not
 > headless.

So, maybe I'm misunderstanding... after it spews the error, it disables
the card?  Well, now, that's annoying.

I dunno what the score with PCI VGA on secondary busses is, but maybe if
you could try putting it in one of the 32-bit slots, it'll work okay.

        -- Jason R. Thorpe <>