Re: [ECOS] General PCI question

[John Newlin <jnewlin at gmail dot com>]

> > This is not specifically an ECOS question, but I'm curious if ECOS handles this.
> >
> > For the chip I am working with, the processor can map into it's
> > virtual address space up to 128MB view into PCI address space.  What
> > happens when the cards in PCI use more than 128MB of address space?
> > Can ECOS swap in and out mappings in the processor address space to
> > access different parts of the PCI space?
> 
> In general, no.  The mappings are contained in registers in the
> PCI configuration space for the card.  There are a fixed [6] number
> of them and they can cover large spaces of either memory or I/O.
> If the card provides a 128MB window and can actually map more than
> that, then you would have to fiddle the configuration registers to
> handle this.  Normally in eCos, we set the configuration registers
> only once, at boot time, to reflect the space that the card says it
> can map and then never fiddle with them again.
> 
> What sort of card would have a 128MB window on a potentially larger
> space?
> 

Some ATI video card.  Not something I would expect to be used in an
embedded system, but I had it, and was just testing that config cycles
were working correctly with multiple devices on the bus.

-John Newlin

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