Why is system tick frequency so high?

RE: Why is system tick frequency so high?

Vidar Berg — Tue, 07 May 2024 12:01:53 GMT

Yes, we use the RTC as the system timer, and nrf_rtc_timer.c is the implementation of it.

[quote userid="76226" url="~/f/nordic-q-a/110954/why-is-system-tick-frequency-so-high/482259"]CONFIG_SYS_CLOCK_TICKS_PER_SEC option controls the frequency of RTC TICK[/quote]

Yes, if you disable the tickles kernel.

RE: Why is system tick frequency so high?

Tamas Selmeci — Tue, 07 May 2024 11:41:02 GMT

So I wasn't wrong when I was unable to find such a SysTick-related code ;)

So Zephyr on Nordic MCUs uses Nordic's RTC which features a low power TICK feature, is it correct? And the CONFIG_SYS_CLOCK_TICKS_PER_SEC option controls the frequency of RTC TICK, is it right? nrf_rtc_timer.c appears to be source file in question...

RE: Why is system tick frequency so high?

Vidar Berg — Tue, 07 May 2024 11:23:19 GMT

Yes, if you don't use the tickless kernel, you should reduce the tick rate. The limitation with using the SysTick timer is that it stops running when the CPU is idle, see Tick event.

It does not look like we have added support for using SysTick in Zephyr.

EDIT: SYS_CLOCK_TICKS_PER_SEC defaults to '128' if you don't select the tickless kernel: https://github.com/nrfconnect/sdk-zephyr/blob/3758bcbfa5cd749d977e2600b6687104b8948243/soc/arm/nordic_nrf/Kconfig.defconfig#L22

RE: Why is system tick frequency so high?

Tamas Selmeci — Tue, 07 May 2024 11:11:24 GMT

And what if I don't use tickless kernel? How to choose from RTC/SysTick sources? (SysTick is a Cortex M4 peripheral in System Control Block, RTC is a vendor-added peripheral)

RE: Why is system tick frequency so high?

Vidar Berg — Tue, 07 May 2024 11:05:40 GMT

Hello,

We use the RTC as the SysTick source to achieve low power, and the 32768 tick rate is chosen because we use the tickless kernel by default. This setting provides better timing granularity.

https://github.com/nrfconnect/sdk-zephyr/blob/b5cf3040298410845311ff7397374540d3451528/kernel/Kconfig#L772

Best regards,

Vidar