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Why is timer15 missing around 7% of the internal events?

Question asked by pointing.mark on Jan 9, 2018
Latest reply on Jan 10, 2018 by pointing.mark

Hi, I have a project with

  • ADC clocked from timer3 using TRG0 on update
  • DMA connected to ADC with interrupt every 200 samples (ping pong style with 400 sample buffer).
  • Timer15 set to clock from timer3 TRG0


The beginning line of the interrupt routine is:

void DMA1_Channel1_IRQHandler(void) {      cntreg1[cntcnt] = TIM15->CNT;      cntreg2[cntcnt++] = DMA1_Channel1->CNDTR;       if (cntcnt == 255)      {           while(1); // BREAKPOINT SET HERE      }
// CLEAR interrupt flags etc. and return below.


When I Examine cntreg2 it has the expected values (200,400,200,400,200,400 etc. etc.)

But when I examine cntreg1 it seems to be missing some of the events.  Actual Values: 175, 347, 523, 712, 911, 1111, 1311, 1510, 1697, 1874, 2054, 2245......


I expect to see 200, 400, 600, 800, 1000, 1200, 1400, etc.


I have tried stopping timer 3 as a test, and timer15 stops counting also, so I think it is safe to assume that I am definitely counting timer3 events.


Has anyone experienced anything like this before? Any ideas why some events are getting missed?