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RE: 600 ns to jump into interrupt routine?

Adam Porsch
Intellectual 385 points

I'm also trying to characterize the context switch latency into my ISR and I see in the disassembly the MMAP qualifier. I see this is needed when trying to access memory mapped location as opposed to a data-memory location.

For example: "AND #63775,mmap(@ST1_55)"

Assuming the AND instruction takes 1 cycle and the mmap instruction takes 1 cycle, does this instruction take 2 cycles to execute? Or, are the instructions done in parallel?

I'm basically trying to determine if I need to add another cycle to my calculation each time I see the mmap qualifier, whether its associated with PSH, AND, OR, etc.

Thanks,

Adam

  • 0
    Genius 4630 points

    As you mentioned in your first sentence, mmap() is a qualifier. It is not an instruction on its own. It modifies other instructions like AND, PSH, OR, etc. I believe that it does not add a cycle.

    I want to point out that there isn't anything actually operating in parallel, because the AND instruction cannot read the unmodified Smem location ... it must instead read the memory-mapped register and only that. It wouldn't really be possible for the DSP to calculate the correct result if these operations were done in parallel, because there can be only one AND calculation stored.

    In addition, parallel instructions are not denoted by a comma, as seen in your example, "AND #63775,mmap(@ST1_55)" but must have a :: or || syntax.

    But it's a fair question in general. If you have Code Composer Studio 3, I believe you can get cycle-accurate simulation of instructions, and that should confirm that AND with the mmap() qualifier is still just 1 cycle.

  • 0 in reply to Brian Willoughby
    TI__Mastermind 43955 points

    HI Adam and Brian,

    I have opened up a new thread on-behalf of you as the questions posted/appended to the very old thread (almost two years ) will get very little attention compared to the new one. The first preference goes to the new thread.

    Probably, from next time onwards, if you would like to continue the conversation in the olf Forum thread, you can open up a new thread and give reference to the old threads by mentioning the forum link.

     

    Regards,

    Shankari