pwm.c

// TeensyCNC
// Copyright 2016 Matt Williams
//
// Motor PWM channel setup and duty cycle setting

#include "MK20D10.h"

void PWM_Init (void) {
  // Enable module clock
  SIM->SCGC6 |= SIM_SCGC6_FTM0_MASK;

  // Set up mode register
  FTM0->MODE = FTM_MODE_FAULTM(0x00) | FTM_MODE_WPDIS_MASK;

  // Clear status and control register
  FTM0->SC = FTM_SC_CLKS(0x00) | FTM_SC_PS(0x00);

  // Clear counter initial register
  FTM0->CNTIN = FTM_CNTIN_INIT(0x00);
  // Reset counter register
  FTM0->CNT = FTM_CNT_COUNT(0x00);

  // Clear channel status and control registers
  FTM0->CONTROLS[0].CnSC = 0x00U;
  FTM0->CONTROLS[1].CnSC = 0x00U;
  FTM0->CONTROLS[2].CnSC = 0x00U;
  FTM0->CONTROLS[3].CnSC = 0x00U;
  FTM0->CONTROLS[4].CnSC = 0x00U;
  FTM0->CONTROLS[5].CnSC = 0x00U;
  FTM0->CONTROLS[6].CnSC = 0x00U;
  FTM0->CONTROLS[7].CnSC = 0x00U;

  // Set up modulo register
  // Bus clock / FTM0_MOD = PWM Freq
  // Bus clock / PWM Freq = FTM0_MOD
  // 36MHz / 1440 = 25KHz (0.04ms)
  // 36MHz / 900 = 40KHz (0.025ms)
  // 36MHz / 288 = 125KHz (0.008ms)
  FTM0->MOD = FTM_MOD_MOD(900 - 1);

  // Set up channel status and control register
  FTM0->CONTROLS[0].CnSC = FTM_CnSC_MSB_MASK | FTM_CnSC_ELSB_MASK | FTM_CnSC_ELSA_MASK;
  // Set up channel value register
  FTM0->CONTROLS[0].CnV = FTM_CnV_VAL(0x00);

  // Set up channel status and control register
  FTM0->CONTROLS[1].CnSC = FTM_CnSC_MSB_MASK | FTM_CnSC_ELSB_MASK | FTM_CnSC_ELSA_MASK;
  // Set up channel value register
  FTM0->CONTROLS[1].CnV = FTM_CnV_VAL(0x00);

  // Set up channel status and control register
  FTM0->CONTROLS[5].CnSC = FTM_CnSC_MSB_MASK | FTM_CnSC_ELSB_MASK | FTM_CnSC_ELSA_MASK;
  // Set up channel value register
  FTM0->CONTROLS[5].CnV = FTM_CnV_VAL(0x00);

  // Set up channel status and control register
  FTM0->CONTROLS[6].CnSC = FTM_CnSC_MSB_MASK | FTM_CnSC_ELSB_MASK | FTM_CnSC_ELSA_MASK;
  // Set up channel value register
  FTM0->CONTROLS[6].CnV = FTM_CnV_VAL(0x00);

  // Set up pin muxes
  PORTC->PCR[1] = (PORTC->PCR[1] & ~(PORT_PCR_ISF_MASK | PORT_PCR_MUX(0x03))) | PORT_PCR_MUX(0x04);
  PORTC->PCR[2] = (PORTC->PCR[2] & ~(PORT_PCR_ISF_MASK | PORT_PCR_MUX(0x03))) | PORT_PCR_MUX(0x04);
  PORTD->PCR[5] = (PORTD->PCR[5] & ~(PORT_PCR_ISF_MASK | PORT_PCR_MUX(0x03))) | PORT_PCR_MUX(0x04);
  PORTD->PCR[6] = (PORTD->PCR[6] & ~(PORT_PCR_ISF_MASK | PORT_PCR_MUX(0x03))) | PORT_PCR_MUX(0x04);

  // Set up status and control register
  FTM0->SC = FTM_SC_CLKS(0x01) | FTM_SC_PS(0x01);
}

void PWM_SetRatio (uint8_t Channel, uint16_t Ratio) {
  uint16_t Period, Duty;
  Period = FTM0->MOD + 1;
  if (Period == 0) {
    Duty = Ratio;
  } else {
    Duty = ((Period * Ratio) + 0x8000U) >> 0x10U;
  }
  FTM0->CONTROLS[Channel].CnV = Duty;
}