PCI caching question related to mvme5500

[Thomas Doerfler (nt)]

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Peter,

I have monitored the current discussion. I am not quite sure what you
actually want to achive with caching the memory area of your PCI card.

Accessing memory over the PCI with single accesses is dead slow, and
this is most likely what happens, when you copy its content to local
memory of you MVME5500. Enabling the data cache for that region will
perform burst accesses, and this will result in a higher troughput, with
the disadvantage of running into cache coherency problems.

Most PCI bridges include some DMA channels. I don't know about the
MVME5500 PCI bridge, but maybe you can use a built-in DMA channel to
transfer content efficently from your PCI card to your local memory?

wkr,
Thomas.


Peter Dufault schrieb:
> 
> On Nov 1, 2005, at 10:51 AM, gregory.menke at gsfc.nasa.gov wrote:
> 
>> It would kind of suck if you put a hardwired exception for your gizmo
>> into the source tree as a patch.  If it is desirable to feed back
>> hardware-specific hacks like this, then I think it would be preferable
>> to implement some kind of hack table in pci.c so that sort of thing
>> could be generalized without making a mess.
>>
> I assume no one would check such a hack in.  I mapped the entire PCI 
> bus in on another BAT cacheable and calculated the offset to get at it.
> 
> I'll look at what you suggested above and try to find a good hack.
> 
> Peter


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Thomas Doerfler           Herbststrasse 8
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