How many system ticks mean 1ms?

RE: How many system ticks mean 1ms?

Einar Thorsrud — Fri, 19 Nov 2021 10:53:11 GMT

Hi John,

[quote user="JohnCC"]Yes. I see. But I worry about systick number. According to my current test. 19885 is mean 1ms. Is this correct?[/quote]

No. 1 ms is 64000 as you wrote before, as this is a 64 MHz clock. I made a small demo to show this:

#include <stdbool.h>
#include <stdint.h>
#include "boards.h"
#include "app_timer.h"
#include "nordic_common.h"
#include "nrf_error.h"
#include "nrf_drv_systick.h"

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

static nrfx_systick_state_t m_systick_state;


static uint32_t ticks_diff_get(nrfx_systick_state_t * p_now, nrfx_systick_state_t * p_old)
{
    return ((p_now->time - p_old->time) & NRF_SYSTICK_VAL_MASK);
}


void clock_initialization()
{
    NRF_CLOCK->LFCLKSRC            = (CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos);
    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
    NRF_CLOCK->TASKS_LFCLKSTART    = 1;

    while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0)
    {
        // Do nothing.
    }
}



APP_TIMER_DEF(m_systick_get_timer_id);

static void systick_get_timer_handler(void * p_context)
{
    nrfx_systick_state_t old_systick_state = m_systick_state;
    nrf_drv_systick_get(&m_systick_state);
    NRF_LOG_INFO("SysTick state: %u (elapsed: %u)",
                 m_systick_state.time,
                 ticks_diff_get(&old_systick_state, &m_systick_state));
}



static void systick_get_timer_init_and_start()
{
    ret_code_t err_code;

    err_code = app_timer_init();
    APP_ERROR_CHECK(err_code);


    err_code = app_timer_create(&m_systick_get_timer_id,
                                APP_TIMER_MODE_REPEATED,
                                systick_get_timer_handler);
    APP_ERROR_CHECK(err_code);

    err_code = app_timer_start(m_systick_get_timer_id, APP_TIMER_TICKS(1), NULL);
    APP_ERROR_CHECK(err_code);
}


int main(void)
{
    clock_initialization();
    systick_get_timer_init_and_start();
    nrf_drv_systick_init();

    APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
    NRF_LOG_DEFAULT_BACKENDS_INIT();

    NRF_LOG_INFO("SysTick demo started.");

    while (true)
    {
        NRF_LOG_FLUSH();
        __SEV();
        __WFE();
        __WFE();
    }
}

Output:

<info> app_timer: RTC: initialized.
<info> app: SysTick demo started.
<info> app: SysTick state: 16712500 (elapsed: 64716)
<info> app: SysTick state: 16649220 (elapsed: 63280)
<info> app: SysTick state: 16585940 (elapsed: 63280)
<info> app: SysTick state: 16522664 (elapsed: 63276)
<info> app: SysTick state: 16459380 (elapsed: 63284)
<info> app: SysTick state: 16396092 (elapsed: 63288)
<info> app: SysTick state: 16332808 (elapsed: 63284)
<info> app: SysTick state: 16269504 (elapsed: 63304)
<info> app: SysTick state: 16079648 (elapsed: 63284)
<info> app: SysTick state: 16016344 (elapsed: 63304)
<info> app: SysTick state: 15953056 (elapsed: 63288)
<info> app: SysTick state: 15889772 (elapsed: 63284)
<info> app: SysTick state: 15826480 (elapsed: 63292)
<info> app: SysTick state: 15763184 (elapsed: 63296)
<info> app: SysTick state: 15699888 (elapsed: 63296)
<info> app: SysTick state: 15636584 (elapsed: 63304)
<info> app: SysTick state: 15573288 (elapsed: 63296)
<info> app: SysTick state: 15509972 (elapsed: 63316)
<info> app: SysTick state: 15446648 (elapsed: 63324)
<info> app: SysTick state: 15383324 (elapsed: 63324)
<info> app: SysTick state: 15320020 (elapsed: 63304)
<info> app: SysTick state: 15256728 (elapsed: 63292)
<info> app: SysTick state: 15193444 (elapsed: 63284)
<info> app: SysTick state: 15130160 (elapsed: 63284)
<info> app: SysTick state: 15066872 (elapsed: 63288)
<info> app: SysTick state: 15003580 (elapsed: 63292)
<info> app: SysTick state: 14877032 (elapsed: 63268)
<info> app: SysTick state: 14813744 (elapsed: 63288)
<info> app: SysTick state: 14750456 (elapsed: 63288)
<info> app: SysTick state: 14687188 (elapsed: 63268)
<info> app: SysTick state: 14623904 (elapsed: 63284)
<info> app: SysTick state: 14560612 (elapsed: 63292)
<info> app: SysTick state: 14497336 (elapsed: 63276)
<info> app: SysTick state: 14434036 (elapsed: 63300)
<info> app: SysTick state: 14370752 (elapsed: 63284)
<info> app: SysTick state: 14244168 (elapsed: 63296)
<info> app: SysTick state: 14180868 (elapsed: 63300)
<info> app: SysTick state: 14117564 (elapsed: 63304)
<info> app: SysTick state: 14054256 (elapsed: 63308)
<info> app: SysTick state: 13990948 (elapsed: 63308)
<info> app: SysTick state: 13927620 (elapsed: 63328)
<info> app: SysTick state: 13864296 (elapsed: 63324)
<info> app: SysTick state: 13800984 (elapsed: 63312)
<info> app: SysTick state: 13737656 (elapsed: 63328)
<info> app: SysTick state: 13674336 (elapsed: 63320)
<info> app: SysTick state: 13611036 (elapsed: 63300)
<info> app: SysTick state: 13547740 (elapsed: 63296)
<info> app: SysTick state: 13484412 (elapsed: 63328)
<info> app: SysTick state: 13357772 (elapsed: 63316)
<info> app: SysTick state: 13294452 (elapsed: 63320)
<info> app: SysTick state: 13231108 (elapsed: 63344)
<info> app: SysTick state: 13167784 (elapsed: 63324)
<info> app: SysTick state: 13104480 (elapsed: 63304)
<info> app: SysTick state: 13041176 (elapsed: 63304)
<info> app: SysTick state: 12977868 (elapsed: 63308)
<info> app: SysTick state: 12914552 (elapsed: 63316)
<info> app: SysTick state: 12851224 (elapsed: 63328)
<info> app: SysTick state: 12724600 (elapsed: 63316)
<info> app: SysTick state: 12661300 (elapsed: 63300)
<info> app: SysTick state: 12598004 (elapsed: 63296)
<info> app: SysTick state: 12534688 (elapsed: 63316)
<info> app: SysTick state: 12471384 (elapsed: 63304)
<info> app: SysTick state: 12408072 (elapsed: 63312)
<info> app: SysTick state: 12344744 (elapsed: 63328)
<info> app: SysTick state: 12281424 (elapsed: 63320)
<info> app: SysTick state: 12218108 (elapsed: 63316)
<info> app: SysTick state: 12154788 (elapsed: 63320)
<info> app: SysTick state: 12091460 (elapsed: 63328)
<info> app: SysTick state: 12028124 (elapsed: 63336)
<info> app: SysTick state: 11964820 (elapsed: 63304)
<info> app: SysTick state: 11838180 (elapsed: 63320)
<info> app: SysTick state: 11774868 (elapsed: 63312)
<info> app: SysTick state: 11711540 (elapsed: 63328)
<info> app: SysTick state: 11648228 (elapsed: 63312)
<info> app: SysTick state: 11584916 (elapsed: 63312)
<info> app: SysTick state: 11521604 (elapsed: 63312)
<info> app: SysTick state: 11458288 (elapsed: 63316)
<info> app: SysTick state: 11394968 (elapsed: 63320)
<info> app: SysTick state: 11331664 (elapsed: 63304)
<info> app: SysTick state: 11078412 (elapsed: 63304)
<info> app: SysTick state: 11015104 (elapsed: 63308)
<info> app: SysTick state: 10951800 (elapsed: 63304)
<info> app: SysTick state: 10888496 (elapsed: 63304)
<info> app: SysTick state: 10825196 (elapsed: 63300)
<info> app: SysTick state: 10761904 (elapsed: 63292)
<info> app: SysTick state: 10698588 (elapsed: 63316)
<info> app: SysTick state: 10635256 (elapsed: 63332)
<info> app: SysTick state: 10571940 (elapsed: 63316)
<info> app: SysTick state: 10508624 (elapsed: 63316)
<info> app: SysTick state: 10445324 (elapsed: 63300)
<info> app: SysTick state: 10382012 (elapsed: 63312)
<info> app: SysTick state: 10318720 (elapsed: 63292)
<info> app: SysTick state: 10255420 (elapsed: 63300)
<info> app: SysTick state: 10192112 (elapsed: 63308)
<info> app: SysTick state: 10128780 (elapsed: 63332)
<info> app: SysTick state: 10065480 (elapsed: 63300)
<info> app: SysTick state: 10002184 (elapsed: 63296)
<info> app: SysTick state: 9938888 (elapsed: 63296)
<info> app: SysTick state: 9875584 (elapsed: 63304)
<info> app: SysTick state: 9812260 (elapsed: 63324)
<info> app: SysTick state: 9748920 (elapsed: 63340)
<info> app: SysTick state: 9685600 (elapsed: 63320)
<info> app: SysTick state: 9622284 (elapsed: 63316)
<info> app: SysTick state: 9558972 (elapsed: 63312)
<info> app: SysTick state: 9495684 (elapsed: 63288)
<info> app: SysTick state: 9432380 (elapsed: 63304)
<info> app: SysTick state: 9369072 (elapsed: 63308)
<info> app: SysTick state: 9305756 (elapsed: 63316)
<info> app: SysTick state: 9242424 (elapsed: 63332)
<info> app: SysTick state: 9179100 (elapsed: 63324)
<info> app: SysTick state: 9115760 (elapsed: 63340)
<info> app: SysTick state: 9052440 (elapsed: 63320)
<info> app: SysTick state: 8989112 (elapsed: 63328)
<info> app: SysTick state: 8925796 (elapsed: 63316)
<info> app: SysTick state: 8609232 (elapsed: 63288)
<info> app: SysTick state: 8545924 (elapsed: 63308)
<info> app: SysTick state: 8482612 (elapsed: 63312)
<info> app: SysTick state: 8419292 (elapsed: 63320)
<info> app: SysTick state: 8355956 (elapsed: 63336)
<info> app: SysTick state: 8292620 (elapsed: 63336)
<info> app: SysTick state: 8229308 (elapsed: 63312)
<info> app: SysTick state: 8165984 (elapsed: 63324)
<info> app: SysTick state: 8102680 (elapsed: 63304)
<info> app: SysTick state: 8039372 (elapsed: 63308)
<info> app: SysTick state: 7976092 (elapsed: 63280)
<info> app: SysTick state: 7912804 (elapsed: 63288)
<info> app: SysTick state: 7849492 (elapsed: 63312)
<info> app: SysTick state: 7786196 (elapsed: 63296)
<info> app: SysTick state: 7722888 (elapsed: 63308)
<info> app: SysTick state: 7659588 (elapsed: 63300)
<info> app: SysTick state: 7596296 (elapsed: 63292)
<info> app: SysTick state: 7533008 (elapsed: 63288)
<info> app: SysTick state: 7469704 (elapsed: 63304)
<info> app: SysTick state: 7406372 (elapsed: 63332)
<info> app: SysTick state: 7343052 (elapsed: 63320)
<info> app: SysTick state: 7279728 (elapsed: 63324)
<info> app: SysTick state: 7216404 (elapsed: 63324)
<info> app: SysTick state: 7153092 (elapsed: 63312)
<info> app: SysTick state: 7089764 (elapsed: 63328)
<info> app: SysTick state: 7026440 (elapsed: 63324)
<info> app: SysTick state: 6963140 (elapsed: 63300)
<info> app: SysTick state: 6899840 (elapsed: 63300)
<info> app: SysTick state: 6836516 (elapsed: 63324)
<info> app: SysTick state: 6773208 (elapsed: 63308)
<info> app: SysTick state: 6709892 (elapsed: 63316)
<info> app: SysTick state: 6583288 (elapsed: 63300)
<info> app: SysTick state: 6519984 (elapsed: 63304)
<info> app: SysTick state: 6456684 (elapsed: 63300)
<info> app: SysTick state: 6393384 (elapsed: 63300)
<info> app: SysTick state: 6330092 (elapsed: 63292)
<info> app: SysTick state: 6266792 (elapsed: 63300)
<info> app: SysTick state: 6203500 (elapsed: 63292)
<info> app: SysTick state: 6140188 (elapsed: 63312)
<info> app: SysTick state: 6076880 (elapsed: 63308)
<info> app: SysTick state: 6013596 (elapsed: 63284)
<info> app: SysTick state: 5697096 (elapsed: 63316)
<info> app: SysTick state: 5633800 (elapsed: 63296)
<info> app: SysTick state: 5570484 (elapsed: 63316)
<info> app: SysTick state: 5507172 (elapsed: 63312)
<info> app: SysTick state: 5443892 (elapsed: 63280)
<info> app: SysTick state: 5380628 (elapsed: 63264)
<info> app: SysTick state: 5317348 (elapsed: 63280)
<info> app: SysTick state: 5254056 (elapsed: 63292)
<info> app: SysTick state: 5190752 (elapsed: 63304)
<info> app: SysTick state: 5127452 (elapsed: 63300)
<info> app: SysTick state: 5064168 (elapsed: 63284)
<info> app: SysTick state: 5000880 (elapsed: 63288)
<info> app: SysTick state: 4937596 (elapsed: 63284)
<info> app: SysTick state: 4874304 (elapsed: 63292)
<info> app: SysTick state: 4811000 (elapsed: 63304)
<info> app: SysTick state: 4747704 (elapsed: 63296)
<info> app: SysTick state: 4684428 (elapsed: 63276)
<info> app: SysTick state: 4621152 (elapsed: 63276)
<info> app: SysTick state: 4557852 (elapsed: 63300)
<info> app: SysTick state: 4494572 (elapsed: 63280)
<info> app: SysTick state: 4431296 (elapsed: 63276)
<info> app: SysTick state: 4367996 (elapsed: 63300)
<info> app: SysTick state: 4304684 (elapsed: 63312)
<info> app: SysTick state: 4241380 (elapsed: 63304)
<info> app: SysTick state: 4178096 (elapsed: 63284)
<info> app: SysTick state: 4114808 (elapsed: 63288)
<info> app: SysTick state: 4051504 (elapsed: 63304)
<info> app: SysTick state: 3988220 (elapsed: 63284)
<info> app: SysTick state: 3924920 (elapsed: 63300)
<info> app: SysTick state: 3861648 (elapsed: 63272)
<info> app: SysTick state: 3671812 (elapsed: 63284)
<info> app: SysTick state: 3608520 (elapsed: 63292)
<info> app: SysTick state: 3545224 (elapsed: 63296)
<info> app: SysTick state: 3481932 (elapsed: 63292)
<info> app: SysTick state: 3418652 (elapsed: 63280)
<info> app: SysTick state: 3355340 (elapsed: 63312)
<info> app: SysTick state: 3292064 (elapsed: 63276)
<info> app: SysTick state: 3228776 (elapsed: 63288)
<info> app: SysTick state: 3165492 (elapsed: 63284)
<info> app: SysTick state: 3102188 (elapsed: 63304)
<info> app: SysTick state: 3038892 (elapsed: 63296)
<info> app: SysTick state: 2975620 (elapsed: 63272)
<info> app: SysTick state: 2912340 (elapsed: 63280)
<info> app: SysTick state: 2849056 (elapsed: 63284)
<info> app: SysTick state: 2785752 (elapsed: 63304)
<info> app: SysTick state: 2722472 (elapsed: 63280)
<info> app: SysTick state: 2659180 (elapsed: 63292)
<info> app: SysTick state: 2595896 (elapsed: 63284)
<info> app: SysTick state: 2532612 (elapsed: 63284)
<info> app: SysTick state: 2469316 (elapsed: 63296)
<info> app: SysTick state: 2406004 (elapsed: 63312)
<info> app: SysTick state: 2152796 (elapsed: 63308)
<info> app: SysTick state: 2089492 (elapsed: 63304)
<info> app: SysTick state: 2026176 (elapsed: 63316)
<info> app: SysTick state: 1962844 (elapsed: 63332)
<info> app: SysTick state: 1899496 (elapsed: 63348)
<info> app: SysTick state: 1836164 (elapsed: 63332)
<info> app: SysTick state: 1772836 (elapsed: 63328)
<info> app: SysTick state: 1709520 (elapsed: 63316)
<info> app: SysTick state: 1646184 (elapsed: 63336)
<info> app: SysTick state: 1582880 (elapsed: 63304)
<info> app: SysTick state: 1519548 (elapsed: 63332)
<info> app: SysTick state: 1456216 (elapsed: 63332)
<info> app: SysTick state: 1392896 (elapsed: 63320)
<info> app: SysTick state: 1329600 (elapsed: 63296)
<info> app: SysTick state: 1266280 (elapsed: 63320)
<info> app: SysTick state: 1202976 (elapsed: 63304)
<info> app: SysTick state: 1139668 (elapsed: 63308)
<info> app: SysTick state: 1076352 (elapsed: 63316)
<info> app: SysTick state: 1013040 (elapsed: 63312)
<info> app: SysTick state: 949732 (elapsed: 63308)
<info> app: SysTick state: 886400 (elapsed: 63332)
<info> app: SysTick state: 759788 (elapsed: 63300)
<info> app: SysTick state: 696496 (elapsed: 63292)
<info> app: SysTick state: 633220 (elapsed: 63276)
<info> app: SysTick state: 569920 (elapsed: 63300)
<info> app: SysTick state: 506616 (elapsed: 63304)
<info> app: SysTick state: 443304 (elapsed: 63312)
<info> app: SysTick state: 380016 (elapsed: 63288)
<info> app: SysTick state: 316712 (elapsed: 63304)
<info> app: SysTick state: 253444 (elapsed: 63268)
<info> app: SysTick state: 190176 (elapsed: 63268)
<info> app: SysTick state: 126888 (elapsed: 63288)
<info> app: SysTick state: 63580 (elapsed: 63308)
<info> app: SysTick state: 284 (elapsed: 63296)
<info> app: SysTick state: 16714188 (elapsed: 63312)
<info> app: SysTick state: 16650884 (elapsed: 63304)
<info> app: SysTick state: 16587596 (elapsed: 63288)
<info> app: SysTick state: 16461000 (elapsed: 63292)
<info> app: SysTick state: 16397700 (elapsed: 63300)
<info> app: SysTick state: 16334392 (elapsed: 63308)
<info> app: SysTick state: 16271100 (elapsed: 63292)
<info> app: SysTick state: 16207788 (elapsed: 63312)
<info> app: SysTick state: 16144496 (elapsed: 63292)
<info> app: SysTick state: 16017916 (elapsed: 63276)
<info> app: SysTick state: 15954636 (elapsed: 63280)
<info> app: SysTick state: 15891356 (elapsed: 63280)
<info> app: SysTick state: 15828064 (elapsed: 63292)
<info> app: SysTick state: 15764796 (elapsed: 63268)
<info> app: SysTick state: 15701504 (elapsed: 63292)
<info> app: SysTick state: 15638216 (elapsed: 63288)
<info> app: SysTick state: 15574920 (elapsed: 63296)
<info> app: SysTick state: 15511616 (elapsed: 63304)
<info> app: SysTick state: 15448328 (elapsed: 63288)
<info> app: SysTick state: 15385028 (elapsed: 63300)
<info> app: SysTick state: 15321740 (elapsed: 63288)
<info> app: SysTick state: 15258460 (elapsed: 63280)
<info> app: SysTick state: 15195184 (elapsed: 63276)
<info> app: SysTick state: 15131892 (elapsed: 63292)
<info> app: SysTick state: 15068604 (elapsed: 63288)
<info> app: SysTick state: 14941988 (elapsed: 63308)
<info> app: SysTick state: 14878700 (elapsed: 63288)
<info> app: SysTick state: 14815416 (elapsed: 63284)
<info> app: SysTick state: 14752136 (elapsed: 63280)
<info> app: SysTick state: 14688852 (elapsed: 63284)
<info> app: SysTick state: 14625568 (elapsed: 63284)
<info> app: SysTick state: 14498972 (elapsed: 63300)
<info> app: SysTick state: 14435664 (elapsed: 63308)
<info> app: SysTick state: 14372372 (elapsed: 63292)
<info> app: SysTick state: 14309076 (elapsed: 63296)
<info> app: SysTick state: 14245760 (elapsed: 63316)
<info> app: SysTick state: 14182456 (elapsed: 63304)
<info> app: SysTick state: 14119160 (elapsed: 63296)
<info> app: SysTick state: 14055856 (elapsed: 63304)
<info> app: SysTick state: 13992540 (elapsed: 63316)
<info> app: SysTick state: 13929232 (elapsed: 63308)
<info> app: SysTick state: 13865940 (elapsed: 63292)
<info> app: SysTick state: 13802648 (elapsed: 63292)
<info> app: SysTick state: 13739348 (elapsed: 63300)
<info> app: SysTick state: 13676060 (elapsed: 63288)
<info> app: SysTick state: 13612748 (elapsed: 63312)
<info> app: SysTick state: 13549444 (elapsed: 63304)
<info> app: SysTick state: 13422864 (elapsed: 63284)
<info> app: SysTick state: 13359588 (elapsed: 63276)
<info> app: SysTick state: 13296316 (elapsed: 63272)
<info> app: SysTick state: 13233028 (elapsed: 63288)
<info> app: SysTick state: 13169724 (elapsed: 63304)
<info> app: SysTick state: 13106432 (elapsed: 63292)
<info> app: SysTick state: 13043124 (elapsed: 63308)
<info> app: SysTick state: 12979804 (elapsed: 63320)
<info> app: SysTick state: 12916508 (elapsed: 63296)
<info> app: SysTick state: 12853192 (elapsed: 63316)
<info> app: SysTick state: 12789884 (elapsed: 63308)
<info> app: SysTick state: 12726588 (elapsed: 63296)
<info> app: SysTick state: 12663276 (elapsed: 63312)
<info> app: SysTick state: 12599968 (elapsed: 63308)
<info> app: SysTick state: 12536660 (elapsed: 63308)
<info> app: SysTick state: 12473352 (elapsed: 63308)
<info> app: SysTick state: 12410036 (elapsed: 63316)
<info> app: SysTick state: 12346704 (elapsed: 63332)
<info> app: SysTick state: 12283388 (elapsed: 63316)
<info> app: SysTick state: 12220064 (elapsed: 63324)
<info> app: SysTick state: 12156744 (elapsed: 63320)
<info> app: SysTick state: 12093420 (elapsed: 63324)
<info> app: SysTick state: 12030112 (elapsed: 63308)
<info> app: SysTick state: 11966800 (elapsed: 63312)
<info> app: SysTick state: 11840192 (elapsed: 63320)
<info> app: SysTick state: 11776876 (elapsed: 63316)
<info> app: SysTick state: 11713544 (elapsed: 63332)
<info> app: SysTick state: 11650220 (elapsed: 63324)
<info> app: SysTick state: 11586912 (elapsed: 63308)
<info> app: SysTick state: 11523612 (elapsed: 63300)
<info> app: SysTick state: 11460320 (elapsed: 63292)
<info> app: SysTick state: 11397040 (elapsed: 63280)
<info> app: SysTick state: 11333748 (elapsed: 63292)
<info> app: SysTick state: 11270440 (elapsed: 63308)
<info> app: SysTick state: 11207128 (elapsed: 63312)
<info> app: SysTick state: 11143820 (elapsed: 63308)
<info> app: SysTick state: 11080500 (elapsed: 63320)
<info> app: SysTick state: 11017180 (elapsed: 63320)
<info> app: SysTick state: 10953872 (elapsed: 63308)
<info> app: SysTick state: 10890536 (elapsed: 63336)
<info> app: SysTick state: 10827224 (elapsed: 63312)
<info> app: SysTick state: 10763916 (elapsed: 63308)
<info> app: SysTick state: 10700588 (elapsed: 63328)
<info> app: SysTick state: 10637256 (elapsed: 63332)
<info> app: SysTick state: 10573940 (elapsed: 63316)
<info> app: SysTick state: 10510640 (elapsed: 63300)
<info> app: SysTick state: 10447332 (elapsed: 63308)
<info> app: SysTick state: 10384036 (elapsed: 63296)
<info> app: SysTick state: 10257448 (elapsed: 63292)
<info> app: SysTick state: 10194132 (elapsed: 63316)
<info> app: SysTick state: 10130824 (elapsed: 63308)
<info> app: SysTick state: 10067528 (elapsed: 63296)
<info> app: SysTick state: 10004220 (elapsed: 63308)
<info> app: SysTick state: 9940916 (elapsed: 63304)
<info> app: SysTick state: 9877596 (elapsed: 63320)
<info> app: SysTick state: 9814284 (elapsed: 63312)
<info> app: SysTick state: 9750996 (elapsed: 63288)
<info> app: SysTick state: 9687704 (elapsed: 63292)
<info> app: SysTick state: 9624412 (elapsed: 63292)
<info> app: SysTick state: 9561112 (elapsed: 63300)
<info> app: SysTick state: 9497808 (elapsed: 63304)
<info> app: SysTick state: 9434500 (elapsed: 63308)
<info> app: SysTick state: 9371204 (elapsed: 63296)
<info> app: SysTick state: 9307920 (elapsed: 63284)
<info> app: SysTick state: 9244616 (elapsed: 63304)
<info> app: SysTick state: 9181312 (elapsed: 63304)
<info> app: SysTick state: 9118004 (elapsed: 63308)
<info> app: SysTick state: 9054704 (elapsed: 63300)
<info> app: SysTick state: 8991400 (elapsed: 63304)
<info> app: SysTick state: 8928084 (elapsed: 63316)
<info> app: SysTick state: 8864784 (elapsed: 63300)
<info> app: SysTick state: 8801460 (elapsed: 63324)
<info> app: SysTick state: 8674836 (elapsed: 63328)
<info> app: SysTick state: 8611532 (elapsed: 63304)
<info> app: SysTick state: 8548232 (elapsed: 63300)
<info> app: SysTick state: 8484920 (elapsed: 63312)
<info> app: SysTick state: 8421592 (elapsed: 63328)
<info> app: SysTick state: 8358276 (elapsed: 63316)
<info> app: SysTick state: 8294936 (elapsed: 63340)
<info> app: SysTick state: 8231620 (elapsed: 63316)
<info> app: SysTick state: 8168308 (elapsed: 63312)
<info> app: SysTick state: 8105000 (elapsed: 63308)
<info> app: SysTick state: 8041692 (elapsed: 63308)
<info> app: SysTick state: 7978376 (elapsed: 63316)
<info> app: SysTick state: 7915068 (elapsed: 63308)
<info> app: SysTick state: 7851756 (elapsed: 63312)
<info> app: SysTick state: 7788460 (elapsed: 63296)
<info> app: SysTick state: 7725164 (elapsed: 63296)
<info> app: SysTick state: 7661876 (elapsed: 63288)
<info> app: SysTick state: 7598584 (elapsed: 63292)
<info> app: SysTick state: 7535276 (elapsed: 63308)
<info> app: SysTick state: 7471996 (elapsed: 63280)
<info> app: SysTick state: 7408724 (elapsed: 63272)
<info> app: SysTick state: 7345440 (elapsed: 63284)
<info> app: SysTick state: 7282156 (elapsed: 63284)
<info> app: SysTick state: 7218876 (elapsed: 63280)
<info> app: SysTick state: 7155620 (elapsed: 63256)
<info> app: SysTick state: 7029084 (elapsed: 63268)
<info> app: SysTick state: 6965828 (elapsed: 63256)

[quote user="JohnCC"]Is there any situation where this value will change?[/quote]

Well, a problem here is that use use another timer to read this value every x time, and that timer will have same variation, depending on its reference clock etc. As you do this in SW, you are also affected by other same or higher priority interrupts etc in a real application, and any critical sections etc (which disabled interrupt for a short time).

Also, this depends on the accuracy of the HFCLK. In my example above I do not start the HFXO, so the accuracy comes from tine HFINT, which has several percent variation.

(Note that if you need to match this time with som external signal from GPIOTE, a timer peripheral would be much more sensible as then you could do this in HW via PPI, so that SW does not introduce any unpredictable delays.)

Edit: I should perhaps mention that the sample I did like this to make it close to what I though you did. If you just want to wait for a duration and get a interrupt at a specific time using SysTick you should refer to the Blinky SysTick Example.

RE: How many system ticks mean 1ms?

JohnCC — Fri, 19 Nov 2021 09:44:51 GMT

Hi,

Yes. I see. But I worry about systick number. According to my current test. 19885 is mean 1ms. Is this correct? Is there any situation where this value will change?

Thank you.

John.

RE: How many system ticks mean 1ms?

Einar Thorsrud — Fri, 19 Nov 2021 09:40:46 GMT

Hi John,

I see. Then this is a special case (one of very few) where the SysTick timer can be a good choice. There are no other timers that give you the same resolution (the next in line would be a TIMER, which on the nRF52832 can be up to 16 MHz).

RE: How many system ticks mean 1ms?

JohnCC — Fri, 19 Nov 2021 08:27:50 GMT

Hi,

This device can be plugged into a power outlet. So don't worry about power consumption issue.

I need a maximum resolution. The bigger the better. That’s why I want to use this method. This is the method with the largest timer resolution I can think about.

Thank you.

John.

RE: How many system ticks mean 1ms?

Einar Thorsrud — Fri, 19 Nov 2021 07:56:08 GMT

Will this cycle computer be battery operated? If so, will this algorithm run continuously? If so this is very likely not a sensibel approach, simply from an energy perspective. As mentioned systick does not work while the CPU is sleeping, so you cannot be low power.

Can you quantify how high resolution you need? If a 32.768 kHz clock is enough, then you can get very low power using an RTC (often via app_timer so you don't need a dedicated RTC instance). If you need higher resolution but with more flexibility, then a TIMER peripheral is what you want.

RE: How many system ticks mean 1ms?

JohnCC — Fri, 19 Nov 2021 01:54:59 GMT

Hi,

In fact, I want to have a number so that I can continue to get it. And the resolution of the number has to be very high.

Because I want to develop cycling cadence algorithm and I want to get systick number. I use last systick number and presen t systick number to get a difference time to calculate.

cadence_time_end = nrf_drv_systick_get_for_cadence();
cadence_time_diff = (0xFFFFFF & (cadence_time_start - cadence_time_end));
cadence_time_start = cadence_time_end;
        
gear_ratio_temp = CalGearRatio(cadence_time_diff);
if(gear_ratio_temp != -1.0)
    v_gear_ratio = gear_ratio_temp;

Or do you have any better suggestions?

RE: How many system ticks mean 1ms?

Einar Thorsrud — Thu, 18 Nov 2021 13:01:31 GMT

Hi,

You are right that the SysTick frequency is 64 MHz. I see in your update you commented out nrf_pwr_mgmt_run(), and in that case you will get predictable values. In most real prodcuts the SysTick implementation is not practical though, as it pauses when the CPU pauses.

I did not understand the use case, but in most practical applications where you want to call a function repeatedly at a specific interval you would want to use the RTC instead, as it runs always and is low power. If that is what you are after, then the app_timer library is probably what you want.

RE: How many system ticks mean 1ms?

JohnCC — Thu, 18 Nov 2021 06:29:23 GMT

Hi,

Add a bit of information.

1. Based on my result. sound like 19885 systicks mean "1ms"

2. I don't use nrf_pwr_mgmt_run()

void main()
{
    for (;;)
    {
        if (m_saadc_calibrate == true) 
        {
            nrf_drv_saadc_abort();
            while(nrf_drv_saadc_calibrate_offset() != NRF_SUCCESS); //Trigger calibration task
            m_saadc_calibrate = false;
        }
        //nrf_pwr_mgmt_run();
    }
}