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rMa1's avatar
rMa1
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5 years ago
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How to set descriptor length dynamically in PCIe Hard IP (AVMM-DMA interface)

In my system, data stream has different length in the three mode, for example, we need descriptor length=128 in mode1, and descriptor length=32 in mode2, descriptor length=100 in mode3, mode set by Host. How to set descriptor length dynamically in PCIe Hard IP (AVMM-DMA interface)?

Thanks. Vicky

  • KhaiChein_Y_Intel's avatar
    KhaiChein_Y_Intel
    4 years ago

    Hi,


    We do not receive any response from you to the previous question/reply/answer that I have provided. This thread will be transitioned to community support. If you have a new question, feel free to open a new thread to get the support from Intel experts. Otherwise, the community users will continue to help you on this thread. Thank you


    Best regards,

    KhaiY


14 Replies

  • KhaiChein_Y_Intel's avatar
    KhaiChein_Y_Intel
    Icon for Regular Contributor rankRegular Contributor
    5 years ago

    Hi Vicky,


    Upon checking, you may use RD_DMA_LAST_PTR (Read) or WR_DMA_LAST_PTR (Write) to control the descriptor length. If 128 descriptors are specified and all of them execute, then descriptor ID 127 is written to the RD_DMA_LAST_PTR or WR_DMA_LAST_PTR register to start the DMA.


    For example, if RD_DMA_LAST_PTR reads 4, the last descriptor requested is 4. To specify 5 more descriptors, software should write a 9 into the RD_DMA_LAST_PTR register. The DMA executes 5 more descriptors. To have the read DMA record the done bit of every descriptor, program this register to transfer one descriptor at a time. RD_TABLE_SIZE specifies the size of the Read descriptor table. The descriptor ID loops back to 0 after reaching RD_TABLE_SIZE. For example, if the RD_DMA_LAST_PTR value read is 126 and you want to execute three more descriptors, software must write 127, and then 1 into the RD_DMA_LAST_PTR register


    You may refer to Intel® Arria® 10 or Intel® Cyclone® 10 GX Avalon® Memory Mapped (AvalonMM) DMA Interface for PCI Express* Solutions User Guide for details.

    https://www.intel.cn/content/dam/www/programmable/us/en/pdfs/literature/ug/ug_a10_pcie_avmm_dma.pdf


    Thanks

    Best regards,

    KhaiY


    • rMa1's avatar
      rMa1
      Icon for New Contributor rankNew Contributor
      5 years ago

      Hi KhaiChein,

      Do you mean RD_TABLE_SIZE could be programed at any time? For example, if I want to use descriptor length is 128, set RD_TABLE_SIZE=128 and RD_DMA_LAST_PTR=127(same as WR_DMA_PTR); then I want to use descriptor length is 15 after descriptor ID loop back to 0, I will set RD_TABLE_SIZE=15 and RD_DMA_LAST_PTR=14, is it right?

      I want to know if descriptor table length could specific dynamically, in the manual, RD_TABLE_SIZE could be set (only) one time, should be set the maximum size, all descriptor ID need to go through until RD_TABLE_SIZE, although some times actually use descriptor length are less than RD_TABLE_SIZE(set by before), I mean it is no need to go though all descriptor ID if we could set RD_TABLE_SIZE any time.

      Please correct me.

      Vicky

  • KhaiChein_Y_Intel's avatar
    KhaiChein_Y_Intel
    Icon for Regular Contributor rankRegular Contributor
    4 years ago

    Hi Vicky,


    The RD_TABLE_SIZE can be set to a new value after all previous programmed DMA descriptor are completed with no pending transaction and the last pointer register has been written with 0.


    The driver, can set this register to 16, then write a new value of last pointer to restart the DMA operation.


    Thanks

    Best regards,

    KhaiY


    • rMa1's avatar
      rMa1
      Icon for New Contributor rankNew Contributor
      4 years ago

      Hi KhaiY,

      Our driver designer could not change RD_TABLE_ZISE when the path is idle, do you have the detail description about this?

      I want to talk with you about this by phone or online meeting if you could support.

      rongli.ma@bsci.com

      Vicky

      • rMa1's avatar
        rMa1
        Icon for New Contributor rankNew Contributor
        4 years ago

        Hi KhaiY，

        I want to explain the details again, when driver set the new value to the RD_TABLE_SIZE register, example RD_TABLE_SIZE=16(set RD_TABLE_SIZE=128 before， after power on), the operation in the descriptor is also go over the 128 descriptor but not 16, just like this register are wrote invalid, but there is no any alarm.

        Vicky

  • KhaiChein_Y_Intel's avatar
    KhaiChein_Y_Intel
    Icon for Regular Contributor rankRegular Contributor
    4 years ago

    Hi Vicky,


    Can you check if (1) the previous programmed DMA descriptor are completed, (2) no pending transaction and (3) the last pointer register has been written with 0 before setting a new value for RD_TABLE_SIZE?


    Thanks

    Best regards,

    KhaiY


    • rMa1's avatar
      rMa1
      Icon for New Contributor rankNew Contributor
      4 years ago

      Sorry, it doesn't work, also as previously can not change the RD_TABLE_SIZE actually.

  • KhaiChein_Y_Intel's avatar
    KhaiChein_Y_Intel
    Icon for Regular Contributor rankRegular Contributor
    4 years ago

    Hi Vicky,


    Could you share the steps you have done and the result of the steps?


    Thanks

    Best regards,

    KhaiY


  • KhaiChein_Y_Intel's avatar
    KhaiChein_Y_Intel
    Icon for Regular Contributor rankRegular Contributor
    4 years ago

    Hi,


    We do not receive any response from you to the previous question/reply/answer that I have provided. This thread will be transitioned to community support. If you have a new question, feel free to open a new thread to get the support from Intel experts. Otherwise, the community users will continue to help you on this thread. Thank you


    Best regards,

    KhaiY


    • rMa1's avatar
      rMa1
      Icon for New Contributor rankNew Contributor
      4 years ago

      Sorry, the RD_TABLE_SIZE can not reset yet now, we will plan to change the DMA solutions later.

  • KhaiChein_Y_Intel's avatar
    KhaiChein_Y_Intel
    Icon for Regular Contributor rankRegular Contributor
    4 years ago

    Hi,


    Sure. You are welcome to open a new thread if you need further assistance in the future.


    Do let me know if you have any thoughts.


    Thanks

    Best regards,

    KhaiY