main.c

/* Copyright (c) 2009 Nordic Semiconductor. All Rights Reserved.
 *
 * The information contained herein is property of Nordic Semiconductor ASA.
 * Terms and conditions of usage are described in detail in NORDIC
 * SEMICONDUCTOR STANDARD SOFTWARE LICENSE AGREEMENT.
 *
 * Licensees are granted free, non-transferable use of the information. NO
 * WARRANTY of ANY KIND is provided. This heading must NOT be removed from
 * the file.
 *
 */

/** @file
 * @brief Simple timer example project with interrupt. Timer is in timer mode.
 * 
 * In this example TIMER2 interrupt is enabled. The TIMER interrupt handler will toggle a LED whenever
 * the TIMER counter is equal to a value of compare register CC[0] or compare register CC[[1]. The timer
 * is set to 16 bit so it will overflow at value 65536 and start from zero. CC[0] and
 * CC[1] register values can be adjusted to change the LED duty cycle. While waiting for TIMER interrupt
 * the CPU is put to sleep in the main loop with the __WFE() __SEV() __WFE() command series.
 *
 * When the timer is in timer mode, it will periodically increment itself. The increment frequency is adjusted
 * by configuring the prescale value. 
 */

#include <stdbool.h>
#include "nrf.h"
#include "nrf_gpio.h"
#include "boards.h"

#define GPIO_TOGGLE_PIN              (LED_0)       /*!< gpio pin to toggle after delay. */


void start_timer(void)
{		
  NRF_TIMER2->MODE = TIMER_MODE_MODE_Timer;  // Set the timer in Counter Mode
  NRF_TIMER2->TASKS_CLEAR = 1;               // clear the task first to be usable for later
	NRF_TIMER2->PRESCALER = 6;                             //Set prescaler. Higher number gives slower timer. Prescaler = 0 gives 16MHz timer
	NRF_TIMER2->BITMODE = TIMER_BITMODE_BITMODE_16Bit;		 //Set counter to 16 bit resolution
	NRF_TIMER2->CC[0] = 25000;                             //Set value for TIMER2 compare register 0
	NRF_TIMER2->CC[1] = 5;                                 //Set value for TIMER2 compare register 1
		
  // Enable interrupt on Timer 2, both for CC[0] and CC[1] compare match events
	NRF_TIMER2->INTENSET = (TIMER_INTENSET_COMPARE0_Enabled << TIMER_INTENSET_COMPARE0_Pos) | (TIMER_INTENSET_COMPARE1_Enabled << TIMER_INTENSET_COMPARE1_Pos);
  NVIC_EnableIRQ(TIMER2_IRQn);
		
  NRF_TIMER2->TASKS_START = 1;               // Start TIMER2
}
		
/** TIMTER2 peripheral interrupt handler. This interrupt handler is called whenever there it a TIMER2 interrupt
 */
void TIMER2_IRQHandler(void)
{
	if ((NRF_TIMER2->EVENTS_COMPARE[0] != 0) && ((NRF_TIMER2->INTENSET & TIMER_INTENSET_COMPARE0_Msk) != 0))
  {
		NRF_TIMER2->EVENTS_COMPARE[0] = 0;           //Clear compare register 0 event	
		nrf_gpio_pin_set(GPIO_TOGGLE_PIN);           //Set LED
  }
	
	if ((NRF_TIMER2->EVENTS_COMPARE[1] != 0) && ((NRF_TIMER2->INTENSET & TIMER_INTENSET_COMPARE1_Msk) != 0))
  {
		NRF_TIMER2->EVENTS_COMPARE[1] = 0;           //Clear compare register 1 event
		nrf_gpio_pin_clear(GPIO_TOGGLE_PIN);         //Clear LED
  }
}

int main(void)
{
	nrf_gpio_cfg_output(GPIO_TOGGLE_PIN);       //Set LED pin as output	
	start_timer();                              //Configure and start timer
	
	while(true) 
	{
		// Enter System ON sleep mode
		__WFE();
		// Make sure any pending events are cleared
		__SEV();
		__WFE();
		
		// For more information on the WFE - SEV - WFE sequence, please refer to the following Devzone article:
		// https://devzone.nordicsemi.com/index.php/how-do-you-put-the-nrf51822-chip-to-sleep#reply-1589
	}
}