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FBuss2's avatar
FBuss2
Icon for New Contributor rankNew Contributor
19 days ago
Solved

Agilex 7 HBM2E burst length

I noticed that I can use a burst length of 1 (arlen/awlen = 0). But the datasheet says "In BL8 mode, the HBMC supports only a burst length of 2 for write and read transactions. If you issue a burst length of 1 in BL8 mode, you will see bresp="10"(SLVERR).". Is the datasheet outdated (for version 25.1.1, didn't find one for 25.3.1 which I'm currently using), or is this undocumented and I shouldn't do this? Would make programming easier, if also burst length 1 is supported.

Core Logic
  • AdzimZM_Altera's avatar
    AdzimZM_Altera
    5 days ago

    Hi FBuss2 ,

     

    HBM2E operates with fixed internal burst lengths (BL4/BL8).

    In BL8 mode, each internal column access returns a full BL8 worth of data.

    A 1‑beat AXI write on a narrow port often forces read‑modify‑write internally; a 1‑beat read fetches a full internal BL8 but delivers only one byte on AXI.

    This is highly inefficient and can degrade throughput and increase power.

     

    Regards,

    Adzim

9 Replies

  • FBuss2's avatar
    FBuss2
    Icon for New Contributor rankNew Contributor
    18 days ago

    And a related question: what is the max burst length? The port is 8 bits wide, but it doesn't work if I use a length greater than 64 in BL8 mode.

    • AdzimZM_Altera's avatar
      AdzimZM_Altera
      Icon for Regular Contributor rankRegular Contributor
      10 days ago

      Hi FBuss2,

       

      Sorry for the delay to reply. I was OOO last week and not able to reply on time.

       

      Can you provide the HBM2E IP setting that you configured?

       

      Are you testing on a Agilex 7 M devkit or a custom board?

       

      Did you used example design to run the test or used your own design?

       

      Regards,

      Adzim

      • FBuss2's avatar
        FBuss2
        Icon for New Contributor rankNew Contributor
        10 days ago

        Here are all the IP configurations of the project: https://frank-buss.de/tmp/ip.zip
        Mostly default settings for the HBM2E IP, just BL8 enabled. I'm using the IA-860m PCIe card, with my own design, based on the card vendor cardtest example. Quartus version is 25.3.1, with patch 1.02 installed.