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AXI terminology - Multiple outstanding , out of order , interleaving

Sandeep Motebennur
Note: This was originally posted on 23rd December 2010 at http://forums.arm.com

Hi All,

In the AXI protocol, can you help me understand in depth about the multiple outstanding addresses, out-of order completion and data interleaving

Scenario 1:
There is Only 1 AXI master (with support of only 1 Master ID) doing transaction to a slave which is capable of handling multiple outstanding addresses.
So Master sets up A0 address and next A1 address. But since Master is capable of only handling single ID, it will place always only 1 valid ID. Is this kind of transaction also referred to as Multiple out standing addresses?

Scenario 2: There is single master with capability of issuing different ID for different transactions. So if there is
A0 with ID 2 and A1 with ID 3, This scenario is called multiple outstanding address. Is my understanding correct?

Scenario 3: In scenario 2, If there are different slaves (1 faster and 1 slower) then how do i issue the out -of order write transaction to different slaves?
Suppose i entered with A0 - ID 2, and A1 - ID 3 on the write address channel and i got the respose of address being accepted. Now i dont know which slave is slow and which is fast. So how do i place my data on the Write data channel? Since the Master dont know which slave is fast or slow, how do i take decision on which data to be placed on Write data channel with corresponding ID and Valid?

I have many querys in Read transactions too. But would like to go step by step in understanding the terms.
Thank you in advance

Best Regards
Sandeep.M
Parents
  • Note: This was originally posted on 27th December 2010 at http://forums.arm.com

    Hello JD,

    Thank you very much. It has cleared lot of questions that i had.

    One concern i had in mind was , out-of order from master - which eventually does not make sense. Thanks for clarifying that out-of-order is only for slaves.
    So any write transaction, unless master supports data interleaving, is a serialized approach.

    Many of read related questions become clear, since the Slaves can support out-of order, so they can send back data to masters with ID.

    Thank you
    Regards
    Sandeep.M
Reply
  • Note: This was originally posted on 27th December 2010 at http://forums.arm.com

    Hello JD,

    Thank you very much. It has cleared lot of questions that i had.

    One concern i had in mind was , out-of order from master - which eventually does not make sense. Thanks for clarifying that out-of-order is only for slaves.
    So any write transaction, unless master supports data interleaving, is a serialized approach.

    Many of read related questions become clear, since the Slaves can support out-of order, so they can send back data to masters with ID.

    Thank you
    Regards
    Sandeep.M
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