FTM for variable pulse widths

JBM — Fri, 21 Jun 2019 02:56:08 GMT

I am trying to get the FTM module to allow me to create a chain of pulses on a GPIO with varying widths -- all with 50% duty cycle and then turn the FTM module off at the end of the train of pulses. I thought I could change the MOD and CnV values in the interrupt, but it doesn't seem to work. Here is the FTM configuration:

ftm_data.data = 0xAAAA;
ftm_data.mask = 0x8000;
// Turn on
SIM_SCGC3 |= SIM_SCGC3_FTM3_MASK;
PORTD_PCR3 = PORT_PCR_MUX(GPIO_PCR_MUX_ALT4) | PORT_PCR_DSE_MASK;
FTM3_MODE |= FTM_MODE_WPDIS_MASK;
FTM3_SC = 0x0;
FTM3_CONF = 0x0;
FTM3_CNT = 0x0;
FTM3_C3SC = FTM_CnSC_MSA(0x1) | FTM_CnSC_ELSA(1) | FTM_CnSC_ELSB(0);
FTM3_MOD = FTM_PERIOD_START;
FTM3_C3V = FTM3_MOD/2;
FTM3_SC = FTM_SC_CLKS(0x1) | FTM_SC_PS(0x0) | FTM_SC_TOIE_MASK;
enable_irq(FTM3_IRQn);

Here is the interrupt:

void FTM3_IRQHandler(void)
{
   if (FTM3_SC & FTM_SC_TOF_MASK)
   {
      FTM3_SC &= ~FTM_SC_TOF_MASK;
      if (ftm_data.mask)
      {
         FTM3_MOD = ftm_data.data & ftm_data.mask ? FTM_PERIOD_LOGICAL_ZERO : FTM_PERIOD_LOGICAL_ONE;
         FTM3_C3V = FTM3_MOD/2;
         FTM3_PWMLOAD |= FTM_PWMLOAD_LDOK_MASK;
         ftm_data.mask >>= 1;
      }
      else
      {
         FTM3_SC = 0x0;
      }
   }
}

The idea was to have an initial pulse period defined by FTM_PERIOD_START in the first code snippet. Then in the interrupt set a long or short pulse depending on the data set in ftm_data.data and'd with ftm_data.mask. The pulse widths I need are anywhere from 6 us to 40 us.

ftm_data is a global structure with two members, data and mask.

Am I going about this the wrong way? What I get is 9 pulses (should be 17). Also, the duty cycle of the first pulse varies and the successive pulses all appear have either a 0 or 100% duty cycle. Not sure what to do at this point.

I'm using the K64 Freedom Board and KDS 3.0, if it matters.

Thanks.

Re: FTM for variable pulse widths

Robin_Shen — Mon, 24 Jun 2019 09:28:00 GMT

Have you try to update the register value in channel interrupt?

For more detail about the register update, please refer "40.4.10 Registers updated from write buffers" of
K64P144M120SF5RM.

Best Regards,

Robin

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Re: FTM for variable pulse widths

JBM — Tue, 16 Jul 2019 21:27:13 GMT

I did. I never got it to work. I was able to do what I need to do with the PIT. This can be closed.

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FTM for variable pulse widths

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Re: FTM for variable pulse widths