RE: non-consistent byte enables

[Terry Trausch <TTrausch@msmail.radisys.com>]

>From PCI System Architecture, Third Edition, MindShare Inc., Tom Shanley/Don 
Anderson, pp. 151-153:

"It is illegal (and makes no sense) for the initiator to assert any byte 
enables of lesser significance than the one indicated by the AD[1:0] 
setting.  If the initiator does assert any of the illegal byte enable 
patterns, the target must terminate the transaction with a target abort ... 
(STOP# asserted, TRDY# and DEVSEL# deasserted) and terminate the transaction 
with no data transferred."

Terry Trausch
RadiSys Corp.
terry.trausch@radisys.com
Beaverton, OR

 ----------
From: pci-sig-request
To: Mailing List Recipients
Subject: non-consistent byte enables
Date: Tuesday, November 12, 1996 11:12AM

Hi everyone,

I'm struggling with the following question:

It says in the spec. (PCI spec. 2.1, pg.22, I/O read command) that
"The byte enables indicate the size of the transfer and must be
consistent with the byte address."  What happens if they are not?

For example, let's say the master requests an I/O read with the
byte address AD(1:0) = 01.  The Target then claims the access by
asserting DEVSEL#, but the byte enables are "0111" which would
correspond to AD(1:0) = 11.  Should the target go ahead and
complete the read in order to provide parity? (pg.29 last paragraph)
If so, does it matter what data is returned?

I'd truly appreciate any insight.

Thanks,
Suzie.
	ô