nrf51822 gpiote and timer capture pulse width

[chenyu]

Hi: I want to capture the parameter of a digital wave like this, I want to get every 't' value. The wave is same in a period of time, but the 51822 capture value of 't' is shaking(the right value is 1500us,and 51822 capture value is 1400 to 1600us random ). I use nrf_drv_gpiote and nrf_drv_timer.My code is as follow. Can you give me some suggestions.

function inital

         const nrf_drv_timer_t TIMER_LED = NRF_DRV_TIMER_INSTANCE(0);    	
         nrf_drv_gpiote_init();
const nrf_drv_gpiote_in_config_t GP_config = 
{
	NRF_GPIOTE_POLARITY_HITOLO,
	NRF_GPIO_PIN_PULLUP,
	false,
	true	
};
nrf_drv_gpiote_in_init(PPM_pin, &GP_config, pin_event_handler);
nrf_drv_gpiote_in_event_addr_get(PPM_pin);

nrf_drv_gpiote_in_event_enable(PPM_pin, true);
const nrf_drv_timer_config_t TI_config = 
{
	NRF_TIMER_FREQ_1MHz,
	NRF_TIMER_MODE_TIMER,
	NRF_TIMER_BIT_WIDTH_32,
	0,
	NULL
};

nrf_drv_timer_init(&TIMER_LED, &TI_config, timer_led_event_handler); nrf_drv_timer_enable(&TIMER_LED);

void pin_event_handler(nrf_drv_gpiote_pin_t pin, nrf_gpiote_polarity_t action)
{
static uint32_t ftime=0,stime=0;
static uint8_t ch_num = 0;
if((pin == PPM_pin) && (action == NRF_GPIOTE_POLARITY_HITOLO))
{
	ftime = nrf_drv_timer_capture(&TIMER_LED,NRF_TIMER_CC_CHANNEL3);
	//printf("%d\n\r",ftime);
	dtime = ftime - stime;
	//printf("%d\n\r",dtime);
	//stime = ftime;
	if(dtime > 2550)
	{
		ch_num = 0;
	}
	else
	{	
			Channel_data[ch_num] = dtime;
			ch_num++;
	}	
	nrf_gpio_pin_toggle(25);
	stime = nrf_drv_timer_capture(&TIMER_LED,NRF_TIMER_CC_CHANNEL3);
}
//NRF_GPIOTE->EVENTS_IN[0] = 0;

}

PS: the dtime is the value I want. Please give me some suggestion. Thank you!

[RK]

If you have the softdevice running it won't work doing it with timer interrupts. Use PPI and a GPIOTE task to capture the timer each edge and then measure it afterw

[chenyu]

I havn't use softdevice. the other mcu hardware I use is gazell/uart/adc. Can gazell disturb gpiote interrupt?

[RK]

Don't know about gazelle - if it has a high enough priority then it could certainly disturb the timing

[chenyu]

I add the ppi function in my code, Fortunately,the capture value error be cut off 50%(50us shaking). But, Is there anyway to thorough solve the program. Thank you!

[chenyu]

I get the timer value in GPIOTE EVENT handler, So I think maybe something disturb the gpiote IRQ.