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Cortex A8 Instruction Cycle Timing

barney vardanyan
Note: This was originally posted on 17th March 2011 at http://forums.arm.com

Hi) sorry for bad English

I need to count latency for two instruction, and all I have is the arm cortex A 8 documantation(charter 16) !
but I have no idea how can do this work using that documantation(
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  • 0
    Note: This was originally posted on 4th May 2011 at http://forums.arm.com


    However, in cycle 2, it  has nop instruction. Why does "nop" occur?



    You can forget the NOP. I add a NOP to the code provided in order to know exactly the time taken by the last instruction.


    About NEOn instructions, how to know that 2 NEON instructions can be dual issue? Do they follow the rule you mentioned?


    Hum. As far as I know, you can believe the cycle counter.
    But It can have mistake (I have some times said wrong things in the past).
    For NEON dual issue, I applied this rules
    http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0344k/BABHBCCB.html

    After I make some test and when I'm not agree with given information I change the rules.
    When I don't find explanation about a technical part, I try to find a model that's seem's to work. Sometime I'm wrong.

    For the cycle counter, the result begin to be quite correct (except for VPf instructions)
    Everytime It's possible, I check that the ccc result is correct by real testing.

    That's all what I can tell you !
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  • 0
    Note: This was originally posted on 4th May 2011 at http://forums.arm.com


    However, in cycle 2, it  has nop instruction. Why does "nop" occur?



    You can forget the NOP. I add a NOP to the code provided in order to know exactly the time taken by the last instruction.


    About NEOn instructions, how to know that 2 NEON instructions can be dual issue? Do they follow the rule you mentioned?


    Hum. As far as I know, you can believe the cycle counter.
    But It can have mistake (I have some times said wrong things in the past).
    For NEON dual issue, I applied this rules
    http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0344k/BABHBCCB.html

    After I make some test and when I'm not agree with given information I change the rules.
    When I don't find explanation about a technical part, I try to find a model that's seem's to work. Sometime I'm wrong.

    For the cycle counter, the result begin to be quite correct (except for VPf instructions)
    Everytime It's possible, I check that the ccc result is correct by real testing.

    That's all what I can tell you !
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