Timer accuracy for micro seconds

[MaximSh]

Hi,

i defined timer 

K_TIMER_DEFINE(my_timer, my_timer_handler, NULL);

then i am starting  the timer with configuration :

k_timer_start(&my_timer, K_USEC(500), K_USEC(500));

The issue that the 

the handler prints log every 581.5 us instead of 500.

What can be the reason?or how to trigger some handler every 500 us

Thanks

[Susheel Nuguru]

The resolution of the kernel timers depend on which clock you are using. We are using RTC on nRF and the configuration CONFIG_SYS_CLOCK_TICKS_PER_SEC is set to 32768 in our samples. 

You should not use k_timer for creating timeouts less than the resolution of the system timer.

[MaximSh]

I try to put K_MSEC(1) but the work handler called after 1.117 ms.
.
i fareget that i changed 

hfclock to 128 MHz but i think it is not related.

static int hfclock_config_and_start(void)
{
	int ret;

	/* Use this to turn on 128 MHz clock for cpu_app */
	ret = nrfx_clock_divider_set(NRF_CLOCK_DOMAIN_HFCLK, NRF_CLOCK_HFCLK_DIV_1);

	ret -= NRFX_ERROR_BASE_NUM;
	if (ret)
	{
		return ret;
	}

	nrfx_clock_hfclk_start();
	while (!nrfx_clock_hfclk_is_running())
	{
	}

	return 0;
}

[MaximSh]

• So how to run polling of some code every 500 microseconds without using timer?
• Why setting 128 MHz clock for cpu_app can't help?
• it is very critical for the aplication to read from SPI data every 500 micro
  
  

Thanks

[Susheel Nuguru]

MaximSh said:

I try to put K_MSEC(1) but the work handler called after 1.117 ms.

Are you calling K_MSEC(1) inside the worker handler or are you queuing the worker handler after K_MSEC(1)? After queuing the work handler, it will not necessary be called immediately if there are higher priority interrupts/threads/worker handlers that are pending to run.

If you want higher resolution timer I recommend you to use the API in modules\hal\nordic\nrfx\drivers\include\nrfx_timer.h

[MaximSh]

Can i use nrfx_timer with zephyr SDK?  or use counter API?

[Susheel Nuguru]

nrfx_timer is OS agnostic, so you can still use it in your application even in Zephyr SDK