NRF54L15 Timer running much slower than expected

RE: NRF54L15 Timer running much slower than expected

Turbo J — Fri, 30 Jan 2026 20:06:21 GMT

Forget interrupt handler, interrupt entry time is variable on ARM Cortex-M CPUs.

Use either a timer with DPPI and GPIOTE - or use the PWM peripherial directly, depending on what you need for your application.

Expected Interrupt jitter with BTLE enabled would be in the 100s of µs - BTLE is very timing critical and the softdevice checks this.

RE: NRF54L15 Timer running much slower than expected

Dan in Colorado — Fri, 30 Jan 2026 18:01:37 GMT

Thank you. That addresses my issue.

A couple follow up questions.

I see that the output on my debug pin varies some from cycle to cycle, I assume this is related to other interrupts having priority. I don't expect I can get around BLE interrupts, but I would like this timer to be as regular as possible. I see in the IRQ_CONNECT marco the IRQ_PRIO_LOWEST VALUE -does this select the lowest possible the lowest priority IRQ, or does it assign the lowest available IRQ number which is the highest priority? Do lower numbered timers has lower number IRQs by default. Asked another way, in a system with several timers, how do I control which one has the highest priority IRQ?

Also, I would like to resync this timer with an periodic external event (a GPIO interrupt) is nrfx_timer_clear() the correct call or is there a better way to resync the timer? Do I need to disable the timer to clear it, or will that just cause an unwanted delay in the syncing process.

RE: NRF54L15 Timer running much slower than expected

Håkon Alseth — Fri, 30 Jan 2026 08:58:32 GMT

Hi,

You are mixing nrfx_timer with the kernel timer.

These are two different modules, and one is sourced from NRF_TIMER (nrfx_timer) and the other is sourced fro the GRTC (k_timer, 31.25 kHz by default).

Since you are using ncs v3.1.1, check out this sample:

https://github.com/zephyrproject-rtos/hal_nordic/blob/a6579483deb33112cc763d05a4a3f8085883c1ac/nrfx/samples/src/nrfx_timer/timer/main.c#L103

located in your sdk-path/modules/hal/nordic/nrfx/samples/src folder.

Kind regards,

Håkon

RE: NRF54L15 Timer running much slower than expected

Dan in Colorado — Thu, 29 Jan 2026 17:49:30 GMT