manual_switch_pulse_measure.c - Uses 16-bit timer to measure pulse width

16-bit Timer2 example: Watches an I/O pin for a low true pulse, records timer value on falling edge, records timer value on rising edge, and uses the difference (delta) of these values to compute the low true pulse width. Assumes that the pulse width does not exceed the maximum timeout value for configured timer. To configure this example to run with an external 8 MHz crystal for for a FCY=40MHz, define the C preprocessor macro: CLOCK_CONFIG=PRIPLL_8MHzCrystal_40MHzFCY and have an external crysal + 2 capacitors on the OSC1/OSC2 pins.

 
#include "pic24_all.h"
#include <stdio.h>

/** \file
 * Measures the pulse width of a pushbutton switch using Timer2 without input capture.
 * CLOCK_CONFIG=PRIPLL_8MHzCrystal_40MHzFCY is defined in the MPLAB project.
 * Remove this macro if you wish to use the internal oscillator.
*/


void  configTimer2(void) {
  T2CON = T2_OFF | T2_IDLE_CON | T2_GATE_OFF
          | T2_32BIT_MODE_OFF
          | T2_SOURCE_INT
          | T2_PS_1_256 ;   //at 40 MHz, approx 420 ms period, 1 tick = 6.4 us
  PR2 = 0xFFFF;                    //maximum period
  TMR2  = 0;                       //clear timer2 value
  _T2IF = 0;                       //clear interrupt flag
  T2CONbits.TON = 1;               //turn on the timer
}

/// Switch1 configuration
inline void CONFIG_SW1()  {
  CONFIG_RB13_AS_DIG_INPUT();     //use RB13 for switch input
  ENABLE_RB13_PULLUP();           //enable the pullup
}
#define SW1              _RB13  //switch state
#define SW1_PRESSED()   SW1==0  //switch test
#define SW1_RELEASED()  SW1==1  //switch test


int main (void) {
  uint16_t u16_start, u16_delta;
  uint32_t u32_pulseWidth;
  configBasic(HELLO_MSG);
  CONFIG_SW1();    //use RB13
  configTimer2();
  while (1) {
    outString("Press button...");
    while (SW1_RELEASED())doHeartbeat();
    u16_start = TMR2;
    while (SW1_PRESSED())doHeartbeat();
    u16_delta = TMR2 - u16_start;  //works because using maximum PR2 value
    u32_pulseWidth = ticksToUs((uint32_t) u16_delta,getTimerPrescale(T2CONbits));
    printf(" %ld us\n",u32_pulseWidth);
  }
}