[ECOS] General PCI question

Gary Thomas gary@mlbassoc.com
Fri Aug 27 15:41:00 GMT 2004

On Fri, 2004-08-27 at 09:07, John Newlin wrote:
> 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

Gary Thomas <gary@mlbassoc.com>
MLB Associates

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