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Bios 5 HWI - GPIO EVENT with DSP 55x

talmor zilberman
Expert 1160 points


folks,

I set GPIO_EVENT as an interrupt (HWI_INT21 in .tcf file) with dispatcher

and encounter 40 micro seconds delay between the interrupt itself  to the time the ISR is called.

does anyone know why? is it related to BIOS ?

Talmor

 

  • 0
    TI__Mastermind 26780 points

    Talmor,

    How are you measuring this delay?  Do you consistently see the same latency?  

    Is it possible that interrupts are disabled at the time the interrupt is triggered, so the ISR cannot run immediately?

    What is the CPU clock rate?

    Scott

  • 0 in reply to ScottG
    Expert 1160 points

    Scott,

    I'm measuring this delay with scop and consistently get the same delay .

    The CPU clock rate is 120 MHz. was able to cut the delay into 5 micro sec

    much better but still a lot . Any idea why?

  • 0 in reply to talmor zilberman
    TI__Mastermind 26780 points

    Talmor,

    OK, thanks.  

    Are you immediately toggling another GPIO at the start of the ISR, and comparing the two on the scope?

    And are you sure there is no interaction with other code or interrupts that may be causing a servicing delay?

    Also, is it possibly an issue with the interrupt configuration of the GPIO, for example, rising versus falling edge triggered, so that the interrupt is not being triggered on the leading edge?

    What did you do to reduce it from 40usec to 5 usec?

    The HWI dispatcher latency is benchmarked with each DSP/BIOS release.  See here for instructions on how to access them: http://processors.wiki.ti.com/index.php/Accessing_DSP/BIOS_and_SYS/BIOS_Benchmarks.  I don’t know which release you are using, but for DSP/BIOS 5.41.12.40 the “HWI_dispatch: Interrupt prolog for calling C function” latency is133 cycles, which would be 1.1usec.

    I see your other thread about not using the dispatcher at all - that will provide a good reference point for investigating this…

    Scott

  • 0 in reply to ScottG
    Expert 1160 points

    Scott,

    once I moved my procedure from main to the task loop I reduce delay from 40 us  to 5 us  :-) (my project is BIOS based)

    once I remove the dispatcher option  i reduce delay from 5 us to 1.2 us

    Talmor