Re: MmMapIoSpace is it really uncached??

From: voidcoder (voidcoder_at_yahoo.com)
Date: 01/25/05 

Date: Tue, 25 Jan 2005 08:50:37 +0100

Yes, You can obtain uncached address with MmMapIoSpace.
But 0x80000000 is cached address. Usually 0x80000000
represents beginning of RAM and has caching enabled.
Un-cached space can be calculated as "cached"+0x20000000.
So, in Your case it is 0xA0000000.

<bigus_dingus@yahoo.com> wrote in message
news:1106604727.344787.284720@f14g2000cwb.googlegroups.com...
> I am using the MmMapIoSpace() system call to attempt to access a
> physical address. I am passing in False for the parameter "CacheType"
> as I most definitely do _not_ want this access to go through the
> processor's cache. However, looking at the bus cycle, I don't believe
> that I am getting an un-cached access. Within OEMAddressTable, this
> area is mapped to virtual address 0x80000000 which I understand is
> un-cached.
> So, my question is this,
>
> Is it possible to get an un-cached address from MmMapIoSpace() if the
> corresponding entry within OEMAddressTable is cached?
>
> ...background:
> Using a Sharp arm processor, the bus will not toggle the chip select
> when sequential accesses to the same chip select areas occur. Some
> hardware has a problem with this. I am creating a barrier function to
> read a different chip select area between successive reads. In the
> barrier function, if I read a cached area, then a bus access does not
> occur. This is what I am seeing when using MmMapIoSpace(my_address, 4,
> FALSE).
>
> anyone...anyone...
> Eric
>

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