0 Replies Latest reply on Oct 2, 2009 11:58 AM by markh@compro.net

    790GX/SB750 PCI-e anomaly/question

    markh@compro.net
      direct dma's between pci-e (1x) and pci-(16x) slots

      I have a number of motherboards with 790GX and 790FX chip sets. Most of which have provided 1 pcie-16x, 2 pcie-1x slots, and 3 regular pci slots. I am using the 16x slot for a VMIC pcie (4x) 5565 reflective memory card. There is on board ATI video. I am attempting to do direct dma from cards (bus masters) on other buses into an out of this VMIC card. I am able to do writes into this card but cannot do reads. I get the same results using the regular pci slots for my dma originator as I do using the pci-e 1x slots. I can do direct dma writes to the card in the 16x slot but can't do reads????

      I can do dma in and out of this VMIC card to/from main memory using it's dma engine no problem.

      I have also a number of motherboards with nvidia chip sets with the same basic slot configuration. I have no problem with this using these MBs.

      Why can't I do bus to bus dma reads out of this card in the 16x slot?

      Any pointers would be appreciated.