PCI I/O space on DEC Alpha machines

[Mitch Norcross <mitch@sunsvr.Pixera.com>]

> On 23 Aug 1996, 11:32:48, Mike wrote:
> >  Stephen  --  Could you explain once again *why* you want
> >  to put any new PCI device into IO space?  I'm having
> >  trouble following the thread related to your initial
> >  question.  If you are not a legacy device, I argue
> >  that no compelling reason exists.  Also what if your
> >  PWB ends up in an Alpha, Power PC, etc.  These *real*
> >  computers don't have IO space and everything ends up
> >  in memory space anyways.

I have a comment on the above, based on my experience with the
Alpha 21064/71/72 chipsets.

Alpha machines do have I/O space (PCI I/O space, that is),
they just don't have I/O instructions.
Access to PCI I/O space is provided through the core logic
chipsets by accessing certain address regions using
load/store instructions.

So, Alpha's lack of I/O instructions is not a reason
to avoid implementing I/O BARs. These machines do provide
access to PCI I/O space.

References:
http://ftp.digital.com/pub/Digital/info/semiconductor/literature/210712ds.pdf
http://www.digital.com:80/.i/info/DTJE04/DTJE04SC.TXT

/Mitch Norcross
 Pixera Corporation
 mitch@pixera.com
 http://www.pixera.com
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