(allocating non-cachable memory) (or More on the i82596)

Justin (Gus) Hurwitz ghurwitz at dyndns.com
Thu Jun 28 20:43:20 EST 2001

Hrm... well, that's not the answer that I wanted, but it does explain a
lot :-/

It sounds like you know a lot more about what's going on here, Paul, but
since it sounds like we're in the same boat, I'm more than willing to help
in whatever way I can (especially since I have nothing better to do until
I get the ethernet controller working, and that just isn't happening
without this fixed :)

And thanks for the heads up that setting PAGE_NO_CACHE doesn't work- I'd
just tried disabling caches entirely and was about to go in and start
mucking with lower level things- starting with a BAT entry :)

Back to the debugger...

On Thu, 28 Jun 2001, Paul White wrote:

> Justin,
> >From my recent experience, this does not work.  We have a device on our
> PCI bus which is DMAing to SDRAM, and so far I can't get anything to
> work without cache coherency support in the system controller.
> If you find anything out, please let me know.  I may end up adding a new
> memory queue for non-cacheable memory, and just use another BAT entry
> for some pre-defined amount of memory for a non-cacheable pool.  A new
> flag to kmalloc() could then be used to get non-cacheable memory.  Does
> anyone know if anything like this already exists, or if theres a much
> easier way around this??  I should hopefully get cache coherency
> working, but we have been unable to so far.  If I end up doing the work,
> I"ll post the patches here.
> Btw..  I attempted to disable cache, as well as simply set the RAM bat's
> to PAGE_NO_CACHE, however this does not work because the PowerPC will
> throw alignment exceptions whenever a cache instruction is called on
> either a non-cached memory region, or if caching is disabled.  Just
> wanted to give you a heads up on this.
> Paul W.
> At 04:52 AM 6/28/2001 -0400, Justin (Gus) Hurwitz wrote:
> >
> >Did yo ever get a reply to this? That sounds like just what I want to do
> >(well, it sounds just like what our vxworks code does to do what I want to
> >do, which I guess is good enough).
> >
> >TIA,
> >--Gus

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