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FBuss2's avatar
FBuss2
Icon for New Contributor rankNew Contributor
4 months 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 l...
Core Logic
  • AdzimZM_Altera's avatar
    AdzimZM_Altera
    3 months 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

FBuss2's avatar
FBuss2
Icon for New Contributor rankNew Contributor
3 months ago

Thanks for the information. If you say "can still run" what does this mean, why do you recommend then to use a burst length 2, if it works? Are there any disadvantages, undefined behavior or anything else if I use burst length 1?

AdzimZM_Altera's avatar
AdzimZM_Altera
Icon for Regular Contributor rankRegular Contributor
3 months 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

  • FBuss2's avatar
    FBuss2
    Icon for New Contributor rankNew Contributor
    3 months ago

    Thanks, this makes sense then to recommend it.