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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

	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 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."