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F28069 ADC High Sampling Frequency

XINJUN DONG
Intellectual 300 points


Hi, guys

I am trying to use F28069 to do high sampling ADC. The sampling frequency should be 2 MHz (period: 500ns). I use PWM SOC to trigger the ADC DAQ. In my ADC interrupt routine, firstly I just tried to clear the flag and acknowledge the interrupt table. Here is the code I use:

AdcRegs.ADCINTFLGCLR.bit.ADCINT1 = 1; //Clear ADCINT1 flag reinitialize for next SOC

PieCtrlRegs.PIEACK.all = PIEACK_GROUP1; // Acknowledge interrupt to PIE.

I am using the CCS5.3.0 debug mode to run the project. I use to clock  in code composer to check that it takes 32 clock cycles to clear the Interrupt flag and another 32 clock cycles to acknowledge the interrupt table, so in total, it takes 800ns just to clear the interrupt in the interrupt routine. I think it takes much longer time than it should be to clear the flag. I know that the debug mode of CCS may lower the actual processing rate of CPU. I was wondering whether it is the reason that causes the problem. If it is, is there anyway to get rid of this disadvantage of debug mode. If it is not, what other reason that causes the problem, and how to fix it to realize the high frequency DAQ. 

Thank you for you time in advance. 

Xinjun

  • 0
    TI__Guru 62975 points

    I don't think that debug mode would make that much of a difference if you are profiling simple register writes.  Which clock are you using to measure the 32-clock cycles?  Between what events are you measuring?

    Taking a step back, can you describe your desired application in more detail?  Is it your intention to process every ADC sample as it completes at 2MHz or will you be working on sets of samples that are spaced out?

  • 0 in reply to tlee
    Intellectual 300 points

    Thank you for your reply.

    I would like to process every ADC sample every 500 ns (2 MHz).  What I use is the clock of CCS itself, and it shows that it takes 32 clocks to process the following command:

    AdcRegs.ADCINTFLGCLR.bit.ADCINT1 = 1; //Clear ADCINT1 flag reinitialize for next SOC.

    Please let me know if you need any other information. Thank you.

    Xinjun

  • 0 in reply to XINJUN DONG
    TI__Guru 62975 points

    You might get a more accurate measurement by reading back the TBCTR register of the same PWM that you use for triggering the SOC.