Re: Claiming 1M when using 8K

["Monish Shah" <monish@hpfcmss.fc.hp.com>]

On Apr 16,  8:24am, Bob Huebner wrote:
> Subject: Claiming 1M when using 8K
> We have designed a PCI Adapter that requires 8K of memory space and 16
> bytes of I/O space for a PC-based application.
> When the memory and I/O BARs are programmed to take 8K and 64 bytes
> and the bits are set to allow them to be placed
> 'anywhere in memory', we have observed one BIOS that puts the 8K
> memory space below the 1Meg limit.
>
> Since this presents the problem of a possible conflict with Legacy ISA
> adapters, we are now thinking of claiming 1M for
> both the I/O and memory BARs to force them into 'upper memory' and
> prevent any possibility of a conflict with an ISA
> device. We have confirmed the BIOS in question now puts the memory
> resource in upper memory.

As other responders have argued, any conflicts here are the BIOS's fault
or the user's fault if the user forgot to tell the BIOS about some non PnP
ISA card.

However, I can imagine that a user who runs into such a problem would not
know enough to place blame accurately.  So, I am sympathetic to your desire
to eliminate the problem.

Still, I think 1 MB is too much to ask for when all you need is 8 KB.  PCI
is showing up in ever larger systems, such that hundreds of PCI slots might
exist in a single system.  If all cards in these slots started asking for a
MB each, there could be problems.

So, I would suggest that you ask for 128 KB only.  Any PC modern enough to
have PCI is bound have full 640KB of base memory and VGA and various BIOS
areas.  The result is that at most 96 KB would be available for mapping PCI
and ISA card's memory spaces below 1M.  So, asking for 128 KB is enough to
guarantee that you'd wind up above 1M.

> Thanks,
> Bob Huebner

Monish Shah
Hewlett Packard
5ìÜ