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AHB Bufferable/Non-bufferable write

Hariprem Arora
Note: This was originally posted on 12th September 2008 at http://forums.arm.com

Hi,

Please clarify the following issue related to AHB write:

If HPROT[2] = 1, AHB write is bufferable and we need to provide OKAY response as soon as the AHB slave interface receives data without caring that the data is actually written into the memory or not.

if HPROT[2] = 0, AHB write is non-bufferable, AHB slave interface needs to provide response to the master only when the data is actually written into the memory.

The issue is that if we see this non-bufferable transaction, the state of HRESP will by default be OKAY (HREADY is HIGH to accept the next data) and it means that we are providing the response in advance for non-bufferable write.

Please clarify how to distinguish between the two transactions.
If possible, please provide waveforms for INCR undefined length & non-bufferable write
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  • 0
    Note: This was originally posted on 16th September 2008 at http://forums.arm.com

    Hi JD,

    Its clear that we need to insert wait states if we want to have destination slave response.

    From here we have following approaches for non-bufferable writes:

    Approach 1 :
    i) Do specified length transfers with last data transfer done by inserting wait state so that real response can be taken for whole burst.
    ii) Do unspecified length transfers with each data transfer done by inserting wait state because slave doesn't know when the last data transfer will occur.

    Approach 2 :
    Remove the unspecified length transfer feature so that it doesn't effect throughput (as wait state is inserted for each data transfer in a burst to get real response).

    Please suggest if the above approaches feasible.

    Hari
Reply
  • 0
    Note: This was originally posted on 16th September 2008 at http://forums.arm.com

    Hi JD,

    Its clear that we need to insert wait states if we want to have destination slave response.

    From here we have following approaches for non-bufferable writes:

    Approach 1 :
    i) Do specified length transfers with last data transfer done by inserting wait state so that real response can be taken for whole burst.
    ii) Do unspecified length transfers with each data transfer done by inserting wait state because slave doesn't know when the last data transfer will occur.

    Approach 2 :
    Remove the unspecified length transfer feature so that it doesn't effect throughput (as wait state is inserted for each data transfer in a burst to get real response).

    Please suggest if the above approaches feasible.

    Hari
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