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PCI DMA Transfert under Windows NT
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- Subject: PCI DMA Transfert under Windows NT
- From: JEAN.J.L.LEROUX@TCETBS1.thomson.fr
- Date: 14 Mar 1997 21:05:33 +0100
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hello PCI experts,
How to get the best performance of DMA transfer (from 4 to 16 Kbytes) on PCI
with use of an AMCC S5933 chip ?
The tests we did, produce a time between a DMA request and the DMA burst on
the
PCI bus proportional to the size of the DMA transfer. We think that's due to
the map
registers implemented (x86 platform) as a set of contiguous non-paged pool
buffers;
the results being a copy of the data performed by the system to ensure
physical address continuity. However, we also observed that this latency
time is sometimes much more shorter (ten times); we suppose no copy
happened.
We tried to limit the transfer size to 4K (size of the page) but we did not
succeed; copies still exit.
Is anyone aware of the problem; What kind of cautions could be taken to
avoid these
costly copies?
Best regards
mail address: lerouxj@tce-rdf.fr
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