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RE: CCS/EK-TM4C129EXL: CPU cycle disassembly, Time of an interrupt (ISR)

Arne Poelaert
Prodigy 170 points

Dear John,

I have one more question.

SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ | SYSCTL_OSC_MAIN | SYSCTL_USE_PLL |SYSCTL_CFG_VCO_480), 120000000);

Those 34 cycles, is correct to say they are at 120MHz or are those 34 cycles at 25MHz (see code above).

Arne

  • 0
    TI__Guru**** 163225 points

    Arne,

    I am not very familiar with the software libraries provided for TM4C.  If you like I could split that question off into a new thread and move to the TM4C forum where they can help.  Or you could post a new thread there.

    Regards,

    John

  • 0 in reply to JohnS
    Prodigy 170 points

    That would be very helpful, thanks!!

    Arne

  • 0 in reply to Arne Poelaert
    TI__Guru**** 191886 points

    Hi,

      Is your question answered by John? I'm not sure what 34 cycles you are referring to? Please bear in mind that cycles is independent of the frequency. If it takes 34 cycles to run an ISR then it does not matter what frequency you are running at, whether at 25MHz or at 120Mhz. In both cases, they all take 34 cycles to complete. It is the absolute time that is different between the two. Running at 120Mhz will certainly complete the task in a shorter time than running at 25Mhz. But the cycles is the same. 

  • 0 in reply to Charles Tsai
    Prodigy 170 points

    I tought at 25MHz 25Million cycles are done per second.

    Thats not true then?

  • 0 in reply to Arne Poelaert
    TI__Guru**** 191886 points

    Hi,

      Yes, 25MHz means 25 million cycles in a second. So what is your question? 

      If you have 100 lines of code and each line takes one cycle to execute then for 100 lines it will take 100 cycles to complete. This is independent of the frequency you are running at, either at 25MHz or 120Mhz. Of course, the 100 lines will complete in a shorter "absolute" time if you were running at 120MHz. That is what I meant.