Caches on MPC8260-like CPUs

[Thomas Doerfler]

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Leon Pollak wrote:
> On Wednesday, 8 בOctober 2008, Thomas Doerfler wrote:
>> Leon,
>>
>> the MPC5200 and the MPC83xx are also based on a 603le core (which is
>> only slightly different). We use the caches there properly. What aspects
>> are you interested in?
>>
>> wkr,
>> Thomas.
> Thank you Thomas.
> 
> I have a general question.
> 
> In MPC860 I had a lot of different ways to fill TLBs so, that I had 1:1 
> virtual memory mapping and still was able to define rather good separation 
> between different cache strategies for my RAM. This was provided by the 
> ability to define rather large pages in TLBs (up to 256MB).
> Thus, I never had the page miss interrupt.
> 
> 
> The MPC8260 TLBs have pages fixed to 4KB, as I was able to understand. And 
> there is 64 of them. This means that I need to use the page miss interrupt to 
> redefine the TLB with still the same 1:1 memory mapping?
> 
> I do not understand something here....
> 
> 
> I thought to use BATs, but there is only 8 of them, which seems to be a bit 
> tight...
> 
> Thank again.

Leon,

as Till already has pointed out, you are stuck with the 8 BAT register
pairs. The good news is that you have eight of them, the original 603
only has 4 (!).

You may use some TLBs additionally for small 4k pages of special stuff.
Keep in mind that AFAIK the BATs have a higher priority than the TLBs if
they are programmed to the same (or an overlapping) address range.

If you collect similar address spaces to a common address range, you may
find a way to live with this limitation.

wkr,
Thomas.


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