Measuring elapsed microseconds between 12 successive rising edges on 12 GPIOS on NRF52832 DK

[Enero]

Hi everyone,

I'm new with nrf52832, and I need to measure elapsed time in microsecond between rising edges of 12 different Gpios. I have 12 piezoelectric sensors filtered, amplified, getting a 0V-3.3V Logic level in input. Once one of these senors rises up, I need to start counting microseconds and store corresponding elapsed microsecond until I have 11 different values (assuming the first sensor's timing is 0). And then posting it over ble.

I red some documentations, and I heard about Timeslot API, timers and sys_tick, but I don't know which one would be better for my application.

Would you have any idea about how should I take this ?

Thanks for your help, and have a good day !

[Krzysztof Zaraska]

Below is my implementation of a microsecond timer. This is old code (SDK 10 for NRF51), so it will not run right away, but should point you in the right direction.

#include "nrf.h"
#include "nrf_drv_timer.h"
#include "bsp.h"

#include "debug.h"

#include "timer.h"

uint64_t timer_micros = 0;

uint32_t timer_ticks; // set in timer_init()
uint32_t timer_interval = 1000000; // us
uint64_t timer_last = 0;

// COMPARE0 is used for overflow
// COMPARE3 is used for reading the timer

int pin_state = 0;

void timer_event_handler(nrf_timer_event_t event_type, void* p_context)
{
	if ( event_type != NRF_TIMER_EVENT_COMPARE0 )
		return;

	if ( pin_state == 0 ) {
		pin_state = 1;
		nrf_gpio_pin_set(PIN_TIMER);
	} else {
		pin_state = 0;
		nrf_gpio_pin_clear(PIN_TIMER);
	}
	
	timer_micros = timer_micros + timer_ticks;
	
	if ( timer_micros >= timer_last + timer_interval ) {
		timer_last = timer_micros;
		timer_callback();
	}
}

// Run on TIMER1
// Timer must be enabled in nrf_drv_config.h
const nrf_drv_timer_t timer = NRF_DRV_TIMER_INSTANCE(1);
nrf_drv_timer_config_t timer_config;

uint64_t timer_read(void)
{
	uint32_t ticks = nrf_drv_timer_capture(&timer, NRF_TIMER_CC_CHANNEL3);
	uint64_t ret = timer_micros + ticks;
	return ret;
}

void timer_init(void)
{
	// TIMER0 is 32-bit, TIMER1 & 2 are 16-bit
	timer_config.bit_width = NRF_TIMER_BIT_WIDTH_16;
	timer_config.frequency = NRF_TIMER_FREQ_1MHz;
	timer_config.interrupt_priority = 1; // 0 = highest, 3 = lowest
	timer_config.mode = NRF_TIMER_MODE_TIMER;
	
	
	uint32_t err_code = NRF_SUCCESS;
	err_code = nrf_drv_timer_init(&timer, &timer_config, timer_event_handler);
	if ( err_code != NRF_SUCCESS )
		_ERROR("nrf_drv_timer_init() failed");
	
	uint32_t time_ms = 50;
	timer_ticks = nrf_drv_timer_ms_to_ticks(&timer, time_ms);
	if ( timer_ticks > 65535 )
		_ERROR("Timer frequency too high");
	
	_DEBUG ("Timer: interrupt every %d ms, %d ticks per interrupt\n", time_ms, timer_ticks);
	
	nrf_drv_timer_extended_compare(
		 &timer, NRF_TIMER_CC_CHANNEL0, timer_ticks, NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, true);
	
	nrf_drv_timer_enable(&timer);
	
}

[Enero]

Thank you for your help, I'm trying to implement it on my code :) Have a good day !

[rusger]

What is PIN_TIMER? There is no definition for it in your code.

[Krzysztof Zaraska]

Number of pin you want to set/clear on timer event. This was copied from a larger project so some defines may be missing.