RE: BAR value of zero?

[Tom Hicks <thicks@fore.com>]

At 02:31 PM 5/26/98 -0700, Brooks Lame wrote:
>> -----Original Message-----
>> From:	Erin Hunter [SMTP:Erin_Hunter@spectrumsignal.com]
>> Sent:	Tuesday, 26 May, 1998 08:26
>> To:	Mailing List Recipients
>> Subject:	BAR value of zero?
>> 
>> Hi,
>> 
>> In section 3.2.2, Addressing, of the PCI spec 2.1 there is a brief
>> mention of a base address register value of zero being invalid (the
>> comment is in the implementation note on Device Address Space).  Is
>> there any more information on this subject in the spec?  How is a PCI
>> core supposed to respond if it is assigned a base address value of
>> zero?
>	[Brooks]  It's not; that's the point and that's how you disable
>individual BARs - set them to zero.  On a related subject, FFFFFFFFh
>_is_ a valid assignment for a BAR and a PCI device should accept that
>value in a config cycle, even though some bits may not be implemented in
>it's address decoder.

care to clarify on that one?  the BAR indicates the window size by NOT
implementing all the bits.  otherwise, how is configuration software to
tell how much memory sits behind a given BAR?

-tom
--
Tom Hicks					FORE Systems
Senior Design Engineer			2000 FORE Drive
ATM Edge Hardware				Warrendale, PA 15086
thicks@fore.com