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P2020/ 85xx PCIe: DMA low throughtput

Question asked by Eran Liberty on Oct 27, 2010
Latest reply on Nov 8, 2010 by Eran Liberty

Hi, I'm working on bring up for a new board based on Freescales p2020. I have a programmable FPGA as a PCIe device with a buffer I can write to and from. I want to test performence for the PCIe bus. I encountered a problem while doing a DMA between the FPGA & DDR. The whole buffer moves to and from the device with out mismatches but with low throughtput. The thing is that the buffer divided to many transactions of byte size instead of transferring it in a burst. I must mention that even a buffer of word size, divided in to byte transactions by the DMA (the core can read a word so it seems like the DMA fault. I tried to change the latency timer, max latency, min latency and cache line in the configuration space of both sides of the pcie bus. It didn't help. I also changed the Band Width Control in the mode registers of the DMA and it didn't help either. Do you have an idea what can it be? Thanks, Natalie.

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