timer.c

#include <stdint.h>
#include "hardware.h"

volatile uint32_t timerCounter = 0;

void init_timer() {
  union {
    uint8_t byte[2];
    unsigned short val;
  } t1cnt;

  // Configure timer to increment timerCounter once every 1ms
  // 1000 is scaling mhz to cycles/msec, 128 is T1CTL.DIV, 2 is TICKSPD
  uint16_t timer_ticks_per_ms = (SYSTEM_CLOCK_MHZ * 1000) / 128 / 2;

  T1CTL = 0x00; // disable timer
  T1CNTL = 0x00; // Clear counter low

  // Start timer in free running mode, no prescaler
  T1CTL = 0x01;

  do {
    t1cnt.byte[0] = T1CNTL;
    t1cnt.byte[1] = T1CNTH; 
  } while (t1cnt.val <= 0xA000);

  // Stop timer
  T1CTL = 0x00;

  // Set period
  T1CC0H = timer_ticks_per_ms >> 8;
  T1CC0L = timer_ticks_per_ms & 0xff;

  T1CCTL0 = 0x44; // Enable int, set output on compare, compare mode, no capture
  TIMIF |= OVFIM; // Enable Timer 1 overflow interrupt mask
  T1IE = 1;
  EA = 1;

  T1CTL = 0x0e;  // TickFreq/128, modulo
}

void reset_timer() {
  timerCounter = 0;
}

void t1_isr(void) __interrupt T1_VECTOR
{
  if (timerCounter % 1000 == 0) {
    //BLUE_LED = !BLUE_LED;
  }
  timerCounter++;
}