PCI caching question related to mvme5500

Peter Dufault dufault at hda.com
Tue Nov 1 20:04:21 UTC 2005

On Nov 1, 2005, at 2:50 PM, Till Straumann wrote:

> No. Currently, PCI memory space is mapped through a BAT as
> cache-inhibited/guarded. Supporting pre-fetchable memory on
> PCI devices would require
>   a) setting up a second mapping marked as cacheable (BAT or
>      pagetables)
>   b) reconfiguring all cacheable devices to use addresses
>      mapped by a)
>   c) resolving coherency issues [probably the hardest]
> Regarding b), note that it is potentially dangerous to
> simply map the same physical address range twice, i.e.,
> both, caching-inhibited and caching-allowed.

I guess I'll stick with my local hack then, which is to map cacheable  
through a BAT and only access the boards sample memory there.  I  
don't get your note, though.   What can happen if you have something  
like that sample memory mapped twice?

It isn't worth signing an NDA and implementing DMA for this application.


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