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Re: PCI I/O vs Memory space



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."