timer in microsecond on nRF52840

[lmouelo]

hello , i'am working actually on the timer of nRF52840 S140  

my timer look like this: 

#define COMPTEUR_INTERVAL     APP_TIMER_TICKS(1)                   /**< Tick / Ms */

APP_TIMER_DEF(sd_timer_id);

static void lfclk_request(void)
{
    ret_code_t err_code;// = nrf_drv_clock_init();
    APP_ERROR_CHECK(err_code);
    nrf_drv_clock_lfclk_request(NULL);
	NRF_LOG_INFO("LFCLK: OFF");
    
    if(nrf_drv_clock_lfclk_is_running()){
		NRF_LOG_INFO("LFCLK: ON");
			
	}
}

void test(){
	
	ret_code_t err_code;
	
	// Create timers
	err_code = app_timer_create(&sd_timer_id,APP_TIMER_MODE_REPEATED,timer_sd_handler);
	lfclk_request();
	APP_ERROR_CHECK(err_code);
	NRF_LOG_INFO("Timer_sd_start");
	err_code = app_timer_start(sd_timer_id, COMPTEUR_INTERVAL, NULL);
	NRF_LOG_INFO("%d",err_code);
	APP_ERROR_CHECK(err_code);
}

static void timer_sd_handler(void * p_context){
	
	compteur++;
	
}

but  how to switch from millisecond resolution to microsecond resolution ? ( APP_TIMER_TICKS) 

thank's

[Jørgen Holmefjord]

Hi,

The application timer library runs using the RTC peripheral, which again use the LFCLK as the clock source. This will give you a maximum frequency of 32.768 kHz, or a resolution of ~30 µs. If you want better resolution, you need to use the TIMER peripheral. There is a driver and an example available in the SDK. Please have a look at this thread for more details.

Best regards,
Jørgen

[Jørgen Holmefjord]

You are not required to use the MACRO defined in the app_timer library. You can calculate the ticks value yourself, or create your own MACRO to calculate ticks from microseconds:

#define APP_TIMER_TICKS_US(US)                                \
            ((uint32_t)ROUNDED_DIV(                        \
            (US) * (uint64_t)APP_TIMER_CLOCK_FREQ,         \
            1000000 * (APP_TIMER_CONFIG_RTC_FREQUENCY + 1)))

[lmouelo]

i have defined the MACRO on app_timer.h like this 

#ifndef FREERTOS
#define APP_TIMER_TICKS(MS)                                \
            ((uint32_t)ROUNDED_DIV(                        \
            (MS) * (uint64_t)APP_TIMER_CLOCK_FREQ,         \
            1000 * (APP_TIMER_CONFIG_RTC_FREQUENCY + 1)))

#define APP_TIMER_TICKS_US(US)                                \
            ((uint32_t)ROUNDED_DIV(                        \
            (US) * (uint64_t)APP_TIMER_CLOCK_FREQ,         \
            1000000 * (APP_TIMER_CONFIG_RTC_FREQUENCY + 1)))
#else
#include "FreeRTOSConfig.h"
#define APP_TIMER_TICKS(MS) (uint32_t)ROUNDED_DIV((MS)*configTICK_RATE_HZ,1000)
#endif

and on my main : 

#define COMPTEUR_INTERVAL     APP_TIMER_TICKS_US(1)                   /**< Tick / Us */void test(){
	
	ret_code_t err_code;
	//Create timers
	err_code = app_timer_create(&timer_id,APP_TIMER_MODE_REPEATED,timer_sd_handler);
	lfclk_request();
	APP_ERROR_CHECK(err_code);
	NRF_LOG_INFO("Timer_sd_start");
	err_code = app_timer_start(timer_id, COMPTEUR_INTERVAL, NULL);
	NRF_LOG_INFO("%d",err_code);
	APP_ERROR_CHECK(err_code);
}

but i have a fatal error when i define like this : 

-> #define COMPTEUR_INTERVAL     APP_TIMER_TICKS_US(1)                   /**< Tick / Us */ 

but no fatal error with this  : 

-> #define COMPTEUR_INTERVAL     APP_TIMER_TICKS_US(1000)                   /**< Tick / Us */

i don't know why 

[Jørgen Holmefjord]

I told you the resolution is 30 µs. You try to calculate ticks for 1 µs. Of course that will not work. App_timer have a minimum tick configuration of 5: APP_TIMER_MIN_TIMEOUT_TICKS, which means you cannot get a timeout of less than ~150 µs.

[lmouelo]

ok i have understood 

thank's