Re: [NILO-discuss] Zen and the art of running in real mode

[Michael B. <mb...@fe...>]

On Wed, 9 Mar 2005, H. Peter Anvin wrote:
> > The MMIO/portio issue is driver-specific.  Drivers that use MMIO will use 
> > readX/writeX.  Since these functions won't work under -DKEEP_IT_REAL, we 
> > could just make the compiler throw an error.
> Right.  With appropriate descriptors set up they could work in 16-bit 
> protected mode, though, for supporting the PM entry point.

They could, but that wouldn't help the code when it's called via the RM 
entry point.

Also, the cards we're talking about are quite likely to need more than 
64kB of data buffers, in which case we can't fit it into the strict UNDI 
model (64kB code + 64kB data+bss+stack, all in base memory) anyway.  We 
have to accept that the PXE specification is actually incompatible with 
some network cards, and plan to carefully violate the spec.

> I have no idea how the FreeBSD people expect their things to work with
> MMIO-based cards.  I suspect they just tried a small number of cards, it
> worked, and they thought they were clever.

I imagine so, though I'd gladly be proved wrong.

Michael