Using Simple Timer with SoftDevice

[Aftab]

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);
}

[Einar Thorsrud]

Hi,

Unless you explicitly start the HFXO (crystal oscillator) the HFINT (RC oscillator) is used, and that has a quite low accuracy. I suggest you start the HFXO and measure again. You can do that for instance using nrf_drv_clock_hfclk_request() or using this code snippet:

    // Start 64 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.
    }

[Aftab]

Hi,

I made sure that 16MHz clock source is being used by using the code you posted above.

Still I see lot's of variation, the clock source have no positive effect on it.

[Einar Thorsrud]

I see.. Are you using custom HW? If so, can you let me know which crystal you are using and if more variants, which CL value the specific one you use have? Also please share your circuitry around the HF crystal and value of your load caps.