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minimum tick using SYS-BIOS on a F28375D Delfino

Robert Wolfe
Mastermind 7860 points
Other Parts Discussed in Thread: SYSBIOS

Hello,

I am setting up a SYS-BIOS project on a F28375D Delfino, and am wondering - what is the minimum tick that can be configured in SYS-BIOS on the processor?

Regards,

Robert

  • 0
    TI__Guru 53195 points

    The minimum is going to depend on how much timer interrupt processing overhead your system can handle given your SYSCLK speed and other interrupts and tasks you have running. You can use the timing benchmarks for Hwis in SYSBIOS to get some idea of how many cycles an empty timer Hwi could take and then consider that on top of that there's some code that SYSBIOS will execute in every tick interrupt as well.

    There is some discussion in this tutorial pdf on Clock and Timer limitations in SYS/BIOS and when it makes sense to switch to a zero-latency interrupt that may be helpful, depending out what you're trying to do by decreasing the tick period.

    Whitney

  • 0 in reply to Whitney Dewey
    Mastermind 7860 points

    Thanks for the info.  Can you give the theoretical minimum tick rate that could be achieved with a 200 Mhz 28375 processor?  I understand practically, it depends on loading, etc. 

    And then, practically, what would you consider the minimum tick rate ... just ball park.  microseconds, milliseconds?

    Robert

  • 0 in reply to Robert Wolfe
    TI__Guru 53195 points

    By default it's set to 1 ms which should be pretty reasonable in most systems. Setting it to 100 us or lower likely be pushing the limits just based off of what I've seen in other E2E posts.

    Do you have a concern with running it at 1 ms? Looking for more granularity for your Task_sleep() or Semaphore time outs?

    Whitney

  • 0 in reply to Whitney Dewey
    Mastermind 7860 points

    1 ms is likely fine for such heartbeat operations.  From that, though, it might be easy to conclude that the lowest tick resolution using SYS-BIOS is 1 ms, which I know is not true. 

    Concern is more on the real-time, hard sampling requirements, which are much quicker.  For example, does SYS-BIOS have the tick resolution to support running sampling of 10 channels at 40 kHz, or higher?  

    Regards,

    Robert

  • 0 in reply to Robert Wolfe
    TI__Guru 53195 points

    The Clock module provides the tick for all Clock instances and the timeout values for things like Semaphores and Task_sleep() calls--your other interrupts aren't bound by the tick rate though. You can still create Hwis that run at faster rates. There's also the option for the "zero-latency interrupt" capability discussed in the pdf I shared in my earlier post for interrupts if the ~360 cycles needed to run the SYS/BIOS dispatcher is too much and the ISR needs to be plugged outside of SYS/BIOS.

    Whitney