Using Simple Timer with SoftDevice

Question

Device: nRF52840

SDK: 16.0.

Softdevice: 6.1.1

Hello,

I'm using Timer 2 peripheral using simple timer driver. It's working fine but I have serious drift/accuracy issue. The timer drifts about 5s in 30mins. I don't understand why so much drift is happening here.

Simple timer sdk_config.h settings:

// <e> SIMPLE_TIMER_ENABLED - app_simple_timer - Simple application timer functionality
//==========================================================
#ifndef SIMPLE_TIMER_ENABLED
#define SIMPLE_TIMER_ENABLED 1
#endif
// <o> SIMPLE_TIMER_CONFIG_FREQUENCY  - Timer frequency if in Timer mode
 
// <0=> 16 MHz 
// <1=> 8 MHz 
// <2=> 4 MHz 
// <3=> 2 MHz 
// <4=> 1 MHz 
// <5=> 500 kHz 
// <6=> 250 kHz 
// <7=> 125 kHz 
// <8=> 62.5 kHz 
// <9=> 31.25 kHz 

#ifndef SIMPLE_TIMER_CONFIG_FREQUENCY
//#define SIMPLE_TIMER_CONFIG_FREQUENCY 4
#define SIMPLE_TIMER_CONFIG_FREQUENCY 9
#endif

// <o> SIMPLE_TIMER_CONFIG_INSTANCE  - TIMER instance used
 
// <0=> 0 
// <1=> 1 
// <2=> 2 
// <3=> 3 
// <4=> 4 

#ifndef SIMPLE_TIMER_CONFIG_INSTANCE
//#define SIMPLE_TIMER_CONFIG_INSTANCE 1
#define SIMPLE_TIMER_CONFIG_INSTANCE 2
#endif

// </e>

The timer code:

#include <stdbool.h>
#include <stdint.h>
#include <string.h>

#include "nordic_common.h"
#include "nrf.h"
#include "app_error.h"
#include "nrf_log.h"
#include "app_timer.h"
#include "nrf_delay.h"
#include "app_simple_timer.h"

#include "scr_execute.h"

//#define TIMEOUT_VALUE                     50000   //50ms, if f=1Mhz
//#define TIMEOUT_VALUE                       31650   // 3s in 10mins   
//#define TIMEOUT_VALUE                       31750   // 1s in 10mins


// used with timer 2, SIMPLE_TIMER_CONFIG_FREQUENCY=9
//#define TIMEOUT_VALUE_1S                       31800   // 1s tick. 7ms in 30min
#define TIMEOUT_VALUE_1S                       31250   // 1s tick
//#define TIMEOUT_VALUE_100MS                       3180   // 100ms tick

// Used with timer 2, SIMPLE_TIMER_CONFIG_FREQUENCY=4 => 1MHz clock
//#define TIMEOUT_VALUE                       50000    // 50ms
//#define T_OUT                               20       // 20*50 = 1000ms = 1s

void timeout_handler(void * p_context);

uint32_t scr_timer_tick=0;
uint32_t scr_timer_tick_100ms=0;

uint32_t timer_tick=0;

void timeout_handler(void * p_context)
{
    //NRF_LOG_INFO("Timer_tick_st: %lu", scr_timer_tick++);
    #ifdef TIMEOUT_VALUE_100MS
    scr_timer_tick_100ms++;
    if (scr_timer_tick_100ms>=10){
        scr_timer_tick_100ms=0;
        scr_timer_tick++;
    }
    #endif

    
    #ifdef TIMEOUT_VALUE
    timer_tick++;
    if (timer_tick >= T_OUT){    
        
        NRF_TIMER2->TASKS_CAPTURE[0] = 1;
        uint32_t counter = NRF_TIMER2->CC[0];
        
        scr_timer_tick++;
        NRF_LOG_INFO("Timer tick=%lu, Counter capture val=%lu", scr_timer_tick, counter);
        timer_tick=0;
        
    }
    #endif
    
    
    #ifdef TIMEOUT_VALUE_1S
    scr_timer_tick++;
    NRF_LOG_INFO("Timer tick=%lu", scr_timer_tick);
    #endif
    
    // Check if 24Hrs (=86400s) have passed, if yes, reset the clock
    if (scr_timer_tick >= 86400){
        scr_timer_tick = 0;
    }

    //scr_execute_chunk();
}

void scr_timer_init(void){
    uint32_t err_code = app_simple_timer_init();
    APP_ERROR_CHECK(err_code);
}

void scr_timer_start(void){
    #ifdef TIMEOUT_VALUE_100MS
    uint32_t err_code = app_simple_timer_start(APP_SIMPLE_TIMER_MODE_REPEATED, timeout_handler, TIMEOUT_VALUE_100MS, NULL);
    #endif

    #ifdef TIMEOUT_VALUE_1S
    uint32_t err_code = app_simple_timer_start(APP_SIMPLE_TIMER_MODE_REPEATED, timeout_handler, TIMEOUT_VALUE_1S, NULL);
    #endif

    #ifdef TIMEOUT_VALUE
    uint32_t err_code = app_simple_timer_start(APP_SIMPLE_TIMER_MODE_REPEATED, timeout_handler, TIMEOUT_VALUE, NULL);
    #endif

    APP_ERROR_CHECK(err_code);
}

void scr_timer_reset(void){
    scr_timer_tick = 0;
}

void scr_timer_stop(void){
    uint32_t err_code = app_simple_timer_stop();
    APP_ERROR_CHECK(err_code);
}