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Re: Zero-copy PXI-X driver for G5 Mac, process access to 7 GB memory

Miller, Larry writes:
>
> 2. Is is possible to write a PCI-X driver that lets our PCI-X card transfer
> data to these blocks of memory directly without a copy. (i.e. a zero-copy
> driver).

No. You can only do transfers to/from up to 2GB at any one time.

All IOKIt "physical" addresses are 32-bit. The G5 uses an IOMMU
(called the DART) which translates real 64-bit physical addresses to
these 32-bit PCI addresses. So you are

a) Not able to get the real physical address via IOKit. The IOKit
routines will give you translated "dart" addresses.

b) If you had a real 64-bit address, the DART would not know what to
do with it. Ie. your transfer would fail.

So your application would at least need to call into the kernel to
prepare() (pin) and release() (unpin) smaller chunks of memory.

I'm in the same boat -- I'd love for a way to give a real 64-bit
address to my device, and a way to make the Dart just pass my transfer
through, and not attempt to translate it. Most other IOMMUs have this
feature.

Drew
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References: 
 >Zero-copy PXI-X driver for G5 Mac, process access to 7 GB memory (From: "Miller, Larry" <email@hidden>)



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