FlexTimer - measuring pulse width

[bluetiger9]

I am trying to measure the pulse width of a PWM signal on a FRDM-K82F board. I am using the FTM0 FlexTimer in dual edge capture mode on channels 6-7. I'm getting the interrupts both for the rising and falling edge of the pulses. My understanding was that pulse width can be calculated  by subtracting the counter values of the two channels. The problem is that as I see these values are always 0.

#include <stdio.h>
#include "main.h"
void FTM0_IRQHandler(void) {
  int status = FTM_GetStatusFlags(FTM0);
  if (status & kFTM_Chnl6Flag) {
  PRINTF("channel6\r\n");
  PRINTF(" cnt %d \r\n", FTM0->CNT);
  PRINTF(" sc %d \r\n", FTM0->CONTROLS[6].CnSC);
  PRINTF(" value 0 %d \r\n", FTM0->CONTROLS[0].CnV);
  PRINTF(" value 1 %d \r\n", FTM0->CONTROLS[1].CnV);
  PRINTF(" value 2 %d \r\n", FTM0->CONTROLS[2].CnV);
  PRINTF(" value 3 %d \r\n", FTM0->CONTROLS[3].CnV);
  PRINTF(" value 4 %d \r\n", FTM0->CONTROLS[4].CnV);
  PRINTF(" value 5 %d \r\n", FTM0->CONTROLS[5].CnV);
  PRINTF(" value 6 %d \r\n", FTM0->CONTROLS[6].CnV);
  PRINTF(" value 7 %d \r\n\r\n\r\n", FTM0->CONTROLS[7].CnV);
  LED_GREEN_ON();
  }
  if (status & kFTM_Chnl7Flag) {
  PRINTF("channel7\r\n");
  PRINTF(" cnt %d \r\n", FTM0->CNT);
  PRINTF(" sc %d \r\n", FTM0->CONTROLS[7].CnSC);
  PRINTF(" value 0 %d \r\n", FTM0->CONTROLS[0].CnV);
  PRINTF(" value 1 %d \r\n", FTM0->CONTROLS[1].CnV);
  PRINTF(" value 2 %d \r\n", FTM0->CONTROLS[2].CnV);
  PRINTF(" value 3 %d \r\n", FTM0->CONTROLS[3].CnV);
  PRINTF(" value 4 %d \r\n", FTM0->CONTROLS[4].CnV);
  PRINTF(" value 5 %d \r\n", FTM0->CONTROLS[5].CnV);
  PRINTF(" value 6 %d \r\n", FTM0->CONTROLS[6].CnV);
  PRINTF(" value 7 %d \r\n\r\n\r\n", FTM0->CONTROLS[7].CnV);
  PRINTF(" pulse width = %d \r\n\r\n\r\n", FTM0->CONTROLS[7].CnV - FTM0->CONTROLS[6].CnV);
  LED_BLUE_ON();
  }
  if (status & kFTM_TimeOverflowFlag) {
  PRINTF("overflow\r\n");
  LED_RED_ON();
  }
  FTM_ClearStatusFlags(FTM0, status);
}
int main(void) {
  /* Init board hardware. */
  BOARD_InitPins();
  BOARD_BootClockRUN();
  BOARD_InitDebugConsole();
  //EnableInterrupts;
  NVIC_EnableIRQ(FTM0_IRQn);
  PRINTF("Start...");
  /* Add your code here */
  CLOCK_EnableClock(kCLOCK_PortD);
  PORT_SetPinMux(BOARD_LED_GREEN_GPIO_PORT, BOARD_LED_GREEN_GPIO_PIN, kPORT_MuxAsGpio);
  PORT_SetPinMux(BOARD_LED_BLUE_GPIO_PORT, BOARD_LED_BLUE_GPIO_PIN, kPORT_MuxAsGpio);
  PORT_SetPinMux(BOARD_LED_RED_GPIO_PORT, BOARD_LED_RED_GPIO_PIN, kPORT_MuxAsGpio);
  // setup PTA1, PTA2 (J2-18,20) as FTM0_CH6, FTM0_CH7
  CLOCK_EnableClock(kCLOCK_PortA);
  PORT_SetPinMux(PORTA, 1, kPORT_MuxAlt3);
  PORT_SetPinMux(PORTA, 2, kPORT_MuxAlt3);
  ftm_config_t ftmInfo;
  FTM_GetDefaultConfig(&ftmInfo);
  ftmInfo.prescale = kFTM_Prescale_Divide_128;
  FTM_Init(FTM0, &ftmInfo);
  //FTM_SetupPwm(FTM0, ftmParam, 2U, kFTM_EdgeAlignedPwm, 24000U, CLOCK_GetFreq(BUS_CLK));
  ftm_dual_edge_capture_param_t param = { kFTM_Continuous, kFTM_RisingEdge, kFTM_FallingEdge };
  FTM_SetupDualEdgeCapture(FTM0, kFTM_Chnl_3, &param, 0);
  //FTM_SetupInputCapture(FTM0, kFTM_Chnl_6, kFTM_RiseAndFallEdge, 0);
  FTM_EnableInterrupts(FTM0,
  kFTM_Chnl6InterruptEnable | kFTM_Chnl7InterruptEnable | kFTM_Chnl3InterruptEnable | kFTM_Chnl4InterruptEnable |
  kFTM_Chnl0InterruptEnable | kFTM_Chnl1InterruptEnable | kFTM_Chnl2InterruptEnable | kFTM_Chnl5InterruptEnable
  | kFTM_TimeOverflowInterruptEnable
  | kFTM_FaultInterruptEnable | kFTM_ReloadInterruptEnable);
  FTM_StartTimer(FTM0, kFTM_SystemClock);
  //FTM_StartTimer(FTM0, kFTM_ExternalClock);
  LED_GREEN_INIT(LOGIC_LED_OFF);
  LED_RED_INIT(LOGIC_LED_OFF);
  LED_BLUE_INIT(LOGIC_LED_OFF);
  while (true) {
  __asm("nop");bbb
  }
}

I tried without interrupts too, pulling the values in while loop, but I'm getting the same values. The result are the same with single edge capture mode too.

Probably I missed something in the setup part or maybe I'm reading the wrong values from wrong place.

Can somebody take look on the above code to see what goes wrong?

Thanks

[jeremyzhou]

Hi Attila,

Thank you for your interest in NXP Semiconductor products and the opportunity to serve you.

I was wondering if you can upload the demo, then I can replicate the kind of issue on the FRDM-K82F board.

I'm looking forward to your reply.

Hope it helps.
Have a great day,
Ping

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[bluetiger9 · Accepted solution]

I think I found the solution. The FTM0->MOD was zero, so the counter counted from 0 to 0. Setting the value to 0xFFFF solves the problem:

FTM0->MOD = 0xFFFF

Thanks!