Disable cache on 74xx

[Mark A. Greer]

Brian,

I know you are aware of this but I *always* experience cache coherency
problems with the GT64260A when Sysclk/Tclk are anything above 100MHz
and I believe that your board is clocked over that.  Try a 100MHz
crystal and see if the problem goes away.

Mark
--
Dan Malek wrote:

>
> Brian Waite wrote:
>
> > .... The memory controller (gt64260) seems to be
>
>> doing something very wrong and it is thought to be a cache coherency
>> issue.
>
>
> The problem is cache coherency is central to the operation of processor
> bus.  One possibility, especially in the example you described, is the gt
> is generating incorrect cache coherency control cycles on the bus.
> Disabling
> the processor cache isn't going to affect this.
>
>> So to prove this, I was asked to try running without any sort of cache.
>
>
> Make sure you disable it in the memory controller as well.
>
>> Hopefully between Gary's information and yours, Dan I can convince
>> people
>> that it is futile.
>
>
> Linux is a very poor diagnostic tool.  When I run Linux and discover this
> type of problem, I reduce it down into a non-Linux diagnostic that can
> generate the same type of bus cycles.  That way you can just flash it
> into
> rom and let some hardware engineer run it over and over without having to
> boot up something as complex as Linux and sorting through millions of
> bus cycles for the failure mode.  With these types of problems you have
> to determine exactly what causes the failure.  Since the processor hangs
> so completely it should be easy to see the condition of the failure.  If
> it is a memory controller timing problem, you should see exactly what
> failed and it should be clear how to program the controller to correct
> it.
>
> Of course, like Ben said, check the errata.
>
> Good Luck.
>
>
>     -- Dan
>
>
>
>
>


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