Re: PC System BIOS and Base Address Register

[Daniele Beccari <Daniele_Beccari@grenoble.hp.com>]

Don James wrote:

>Your base address registers do not have to be contiguous. Any BIOS that
>stops searching when it finds a BAR of 0 will not pass the PCI SIG's
>compliance tests (specifically the PCIPOST test).

and David O'Shea wrote:

>System BIOS are supposed to scan all of the Base Address Registers,
>even if earlier registers were all 0's.   The operating systems which
>scan the BAR's also adhere to the requirement.   So your implimentation
>is accetable. 

in answer to w_wong@emulex.com:

> PCI Base Address Registers has total of 6 double words. Can
> system BIOS skip unused one and allocate resources to
> non-sequential Base Address Registers? In other word, I used
> only Offset 10h, 18h and 20h Base Address Registers and Skip
> 14h and 1Ch Base Address Registers which are filled with zeros.


I understand this is just a detail, and it is a good thing that
BIOSes scan all BARs. However, we should talk about DEVICE compliance
and not BIOS compliance.

A spec is a spec and the PCI spec says (as reported also by Bob
Goudreau):
	
	"The first Base Address register is always located at offset
	10h.  The second register may be at offset 14h or 18h
	depending on the size of the first.  The offsets of 
	subsequent Base Address registers are determined by the 
	size of previous Base Address registers."

So, w_wong@emulex.com's implementation, whether acceptable, is
unfortunately not respecting the PCI spec (since he is not using 
64 bits addressing, he must use 14h for his second BAR). Unless
somebody can prove that "may be" is to be interpreted as
"if you want it can be"...

What is the impact of this divergence from the spec? None, thanks
to those who wrote the BIOS compliance tests. But maybe future revisions
of the spec should have one more line to clear up this issue more
precisely.

Thanks for your attention,

				
				Daniele





__________________________________________________________
Daniele Beccari            Daniele_Beccari@grenoble.hp.com
Hewlett-Packard, Enterprise Networking & Security Division
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