Setting TIMER2 interval

[Jarmo]

How do I set TIMER2 to interrupt every 1 ms?

Sounds like a very basic question, but I haven't succeed. For TIMER1 I can get it working, but for TIMER2 the highest frequecy I have achieved is about 100 Hz.

The code is as follows:

void init_timer2(void)
{
	// Start 32 MHz crystal oscillator
	NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
	NRF_CLOCK->TASKS_HFCLKSTART = 1;
	// Wait for the external oscillator to start up
	while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) {
		// Do nothing.
	}
	NRF_TIMER2->MODE = TIMER_MODE_MODE_Timer;
	NRF_TIMER2->PRESCALER = 4; // what should be here?
	NVIC_EnableIRQ(TIMER2_IRQn);
        NRF_TIMER2->BITMODE = TIMER_BITMODE_BITMODE_16Bit;
        NRF_TIMER2->CC[0] = ???;
        NRF_TIMER2->CC[1] = ???;
        NRF_TIMER2->CC[2] = ???;
        NRF_TIMER2->CC[3] = ???; 
	NRF_TIMER2->INTENSET = TIMER_INTENSET_COMPARE2_Enabled
	<< TIMER_INTENSET_COMPARE2_Pos;
	sd_softdevice_forward_to_application();
	NRF_TIMER2->TASKS_START = 1;
}

I don't know what should be put into the place of '???'s above. I guess there is a good documentation somewhere, so I would be happy to get a pointer there, too. Indeed, a working code would be best.

Edit: Format (please use preformatted text button when inserting code)

[Håkon Alseth]

Hi,

The prescaler sets the base timer tick like this (given in us): TimerTick = 16M / 2^prescaler.

For instance, if we set 4: TimerTick = 16M/2^4 = 1 us.

In order to generate an interrupt each 1ms:

#define TIMER2_CC_DELAY 1000
...
NRF_TIMER2->PRESCALER = 4;
NRF_TIMER2->CC[0] = TIMER2_CC_DELAY; // Fbase = 16M/2^4 * 1000 = 1 ms.
/*Reset of init*/

In your handler:

void TIMER2_IRQHandler(void)
{    
    if(NRF_TIMER2->EVENTS_COMPARE[0])
    {
        nrf_gpio_pin_toggle(18);
        NRF_TIMER2->EVENTS_COMPARE[0] = 0;
        // Need to update the CC[0]
        NRF_TIMER2->CC[0] += TIMER2_CC_DELAY;
    }
}

For a more precise measurement you can add a static variable inside the interrupt handler to count instead of reading the CC[]-register.

Best regards Håkon

[Håkon Alseth]

Hi Jarmo,

It's most likely because you enabled CC[2]: NRF_TIMER2->INTENSET = TIMER_INTENSET_COMPARE2_Enabled Enabling CC[0] is done like this: NRF_TIMER2->INTENSET = TIMER_INTENSET_COMPARE0_Enabled

BR Håkon