TPM PWM Noise

songja — Tue, 07 May 2019 12:50:25 GMT

Hello,

I have modified the TPM_PWM example to use freeRTOS and drive a motor.

The PWM signal was very noisy when I checked with an oscilloscope and also with a motor controller as shown below.

I changed the PWM frequency and for some reasons, it seemed to work better with higher frequency then stopped working after some value.

When I was checking with the oscilloscope, the measuring frequency was also changing. I assume there might be something wrong with the TPM source clock?

Here is the code I used and the TPM1_CH0 pin was used to send PWM out.

What the code does is, once the SW3 button is pressed and Motor_Switch is true, the sinusoidal duty cycle of PWM is sent out.

/* Interrupt to enable and flag to read; depends on the TPM channel used */
#define TPM_CHANNEL_INTERRUPT_ENABLE kTPM_Chnl1InterruptEnable
#define TPM_CHANNEL_FLAG kTPM_Chnl1Flag

/* Get source clock for TPM driver */
#define TPM_SOURCE_CLOCK CLOCK_GetFreq(kCLOCK_PllFllSelClk)

void vMotor_Control_Task(void)
{
volatile uint16_t updatedDutycycle=0;
TickType_t xLastWakeTime;

tpm_config_t tpmInfo;
tpm_chnl_pwm_signal_param_t tpmParam;

#ifndef TPM_LED_ON_LEVEL
   #define TPM_LED_ON_LEVEL kTPM_HighTrue
#endif
   tpmParam.chnlNumber = (tpm_chnl_t)TPM_CHANNEL;
   tpmParam.level = TPM_LED_ON_LEVEL;
   tpmParam.dutyCyclePercent = 100U;

   /* TPM known issue of KL81, enable clock of TPM0 to use other TPM module */
   CLOCK_EnableClock(kCLOCK_Tpm1);
   /* Select the clock source for the TPM counter as kCLOCK_PllFllSelClk */
   CLOCK_SetTpmClock(1U);

   TPM_GetDefaultConfig(&tpmInfo);
   /* Initialize TPM module */
   TPM_Init(TPM_BASEADDR, &tpmInfo);
   TPM_SetupPwm(TPM_BASEADDR, &tpmParam, 1U, kTPM_EdgeAlignedPwm, 5000U, TPM_SOURCE_CLOCK);
   TPM_StartTimer(TPM_BASEADDR, kTPM_SystemClock);
   TPM_EnableInterrupts(TPM_BASEADDR,TPM_CHANNEL_INTERRUPT_ENABLE);

/* Disable channel output before updating the dutycycle */
TPM_UpdateChnlEdgeLevelSelect(TPM_BASEADDR, (tpm_chnl_t)TPM_CHANNEL, 0U);

   int Motor_Switch = -1;
   uint16_t Sin_time = 0;
   while (1)
   {
      xLastWakeTime = xTaskGetTickCount();

      if (g_ButtonPress)
      {
         PRINTF(" %s is pressed \r\n", BOARD_SW_NAME);
         GPIO_PortToggle(BOARD_LED_GPIO, 1U << BOARD_LED_GPIO_PIN);
         GPIO_PortToggle(EDO_GPIO, 1U << EDO_PIN);
         Motor_Switch *= -1;
         g_ButtonPress = false;
         if(Motor_Switch==1)
         {
            PRINTF("Duty Cycle is on \r\n");

         }
         else
         {
            PRINTF("Duty Cycle is off \r\n");
            Sin_time = 0;
            updatedDutycycle = 100;
         }
      }
      if (Motor_Switch==1)
      {
         updatedDutycycle = (uint16_t) 450 + 350*sin(2*PI*Sin_time/1000-PI/2);
         /* Disable channel output before updating the dutycycle */
         TPM_UpdateChnlEdgeLevelSelect(TPM_BASEADDR, (tpm_chnl_t)TPM_CHANNEL, 0U);

/* Update PWM duty cycle */
TPM_UpdatePwmDutycycle(TPM_BASEADDR, (tpm_chnl_t)TPM_CHANNEL, kTPM_EdgeAlignedPwm, updatedDutycycle);

         /* Start channel output with updated dutycycle */
         TPM_UpdateChnlEdgeLevelSelect(TPM_BASEADDR, (tpm_chnl_t)TPM_CHANNEL, TPM_LED_ON_LEVEL);
         Sin_time++;
      }
      else
      {
         TPM_UpdateChnlEdgeLevelSelect(TPM_BASEADDR, (tpm_chnl_t)TPM_CHANNEL, 0U);
         TPM_UpdatePwmDutycycle(TPM_BASEADDR, (tpm_chnl_t)TPM_CHANNEL, kTPM_EdgeAlignedPwm, 100U);
         TPM_UpdateChnlEdgeLevelSelect(TPM_BASEADDR, (tpm_chnl_t)TPM_CHANNEL, TPM_LED_ON_LEVEL);
      }

vTaskDelayUntil(&xLastWakeTime, 1);
}
}

Thank you.

Re: TPM PWM Noise

jingpan — Thu, 09 May 2019 08:08:17 GMT

Hi Yaeyong,

If you want PWM change continuously, you can't call TPM_UpdateChnlEdgeLevelSelect() before and after TPM_UpdatePwmDutycycle().

If you call TPM_UpdateChnlEdgeLevelSelect() and then TPM_UpdatePwmDutycycle, register TPM.C0V will update immediately. Current PWM waveform will be incomplete.

Another problem in your code is

updatedDutycycle = (uint16_t) 450 + 350*sin(2*PI*Sin_time/1000-PI/2);

updatedDutycycle is a uint8_t type. But your expression show that updatedDutycycle's value is from 100~800.

Regards,

Jing

Re: TPM PWM Noise

songja — Fri, 10 May 2019 09:42:23 GMT

Hello Jing,

Removing TPM_UpdateChnlEdgeLevelSelect() worked.

And I actually set updatedDutycycle to uint16_t before the attached code. Thanks for pointing it out though.

Thanks!.

Regards,

Jay

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