[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: PCI I/O vs Memory space
- To: Mailing List Recipients <pci-sig-request@znyx.com>
- Subject: Re: PCI I/O vs Memory space
- From: jww@anchor.eng.hou.compaq.com (Jeff Wolford)
- Date: Thu, 29 Aug 96 9:51:10 CDT
- Resent-Date: Thu, 29 Aug 96 9:51:10 CDT
- Resent-From: pci-sig-request@znyx.com
- Resent-Message-Id: <"Dv8xz.0.n12.wiR9o"@dart>
- Resent-Sender: pci-sig-request@znyx.com
Re: PCI Memory vs I/O Space...
One of the big differences is that I/O space has the following
properties:
1) Non postable
2) Non prefetchable
3) Non write gatherable
4) Real time completion order is maintained.
This is why the new ACPI control space is in I/O space,
so real time completion order is maintained during a
power down/up of a subsystem.
Some of the above can be corrected by the memory attributes, but
not all and its not clear to me who would set up these
memory attributes for a I/O card.
Q: Anyone have any insight into who/how a x86 PCI machine would
set up the memory attributes.
Q: Any one else have other reasons to use I/O space instead
of memory space or visa-versa.
Jeff
--
Jeff Wolford INTERNET: jww@compaq.com
Senior Member of Technical Staff
Advanced Architecture - Advanced Technology Development
Compaq Computer Corp
(713) 514-9465
"The views expressed here are my own, and not those of my employer."
ð ß