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AHB split retry response

Note: This was originally posted on 9th December 2008 at http://forums.arm.com

IN AMBA AHB , there are split and retry response. These are 2 cycle responses.
whole SPLIT sequence is given in the spec. but my doubt is in which scenario slave
has to to issue SPLIT and RETRY response?

Waiting for the reply. Thanks in advance.
  • Note: This was originally posted on 9th December 2008 at http://forums.arm.com

    Visiuser,

    An AHB slave never *has* to give a SPLIT or a RETRY response; these responses are simply optimisations such that a slave which knows it is going to take a long time to provide the requested data can, potentially, offer improved overall system performance.

    It would be perfectly legal for a simple AHB slave to only implement OK (as an aside, AHB-Lite only supports OK and ERROR).

    hth
    s.



    Hi,

    For simple AHB slave only ERROR and OK responses are fine. but if I have multiple master
    and slaves , then I think I need to give SPLIT  and RETRY responses both. I understood point
    behind SPLIT  response .

    But for RETRY response what will be the scenario??

    Thanks ,
    vlsiuser
  • Note: This was originally posted on 10th December 2008 at http://forums.arm.com

    Hi vlsiuser...

    Actually when to generate split and retry is highly dependent on the system architecture...
    and also the designer...

    When slave cannot respond to the master in predefined wait states..
    Split or retry is given for better bus usage.. so other master can access the bus...



    Hi,

    Yes you are right. It depends on system architecture. but what my doubt is, in which situation
    slave will not respond to master. and for how many cycles master will wait ?

    and is it like SPLIT and RETRY response are possible in case of multiple master and multiple
    slaves?

    Thanks,
    vlsiuser.
  • Note: This was originally posted on 10th December 2008 at http://forums.arm.com

    Hi,

    For simple AHB slave only ERROR and OK responses are fine. but if I have multiple master
    and slaves , then I think I need to give SPLIT  and RETRY responses both. I understood point
    behind SPLIT  response .

    But for RETRY response what will be the scenario??

    Thanks ,
    vlsiuser



    Hi vlsiuser...

    Actually when to generate split and retry is highly dependent on the system architecture...
    and also the designer...

    When slave cannot respond to the master in predefined wait states..
    Split or retry is given for better bus usage.. so other master can access the bus...
  • Note: This was originally posted on 10th December 2008 at http://forums.arm.com

    Yes you are right. It depends on system architecture. but what my doubt is, in which situation
    slave will not respond to master. and for how many cycles master will wait ?

    and is it like SPLIT and RETRY response are possible in case of multiple master and multiple
    slaves?


    I have been having a look at ARM's FAQs recently, and have found a section dedicated to SPLIT/RETRY...may be a good hunting ground for you

    [url="http://www.arm.com/support/AHB_Split_Retry.html"]http://www.arm.com/support/AHB_Split_Retry.html[/url]

    With respect to how long a master will wait, there is no defined maximum value that I could see in the AHB spec. It should simply re-attempt the access when it sees either of these responses, and the time it takes to complete that access will depend on the slave and arbiter design.

    HTH

    :)
  • Note: This was originally posted on 9th December 2008 at http://forums.arm.com

    Visiuser,

    An AHB slave never *has* to give a SPLIT or a RETRY response; these responses are simply optimisations such that a slave which knows it is going to take a long time to provide the requested data can, potentially, offer improved overall system performance.

    It would be perfectly legal for a simple AHB slave to only implement OK (as an aside, AHB-Lite only supports OK and ERROR).

    hth
    s.