RE: nRF54L15 GRTC -> GPPI -> GPIOTE pipeline

Susheel Nuguru — Fri, 27 Jun 2025 09:13:14 GMT

Hi Jeremy,

Unlike RTC all GRTC compare channels are one shot. Once they are fired, then it seems that there is no automatic (no CPU involved) way to reload them. You wired

CC1 → PPI → GPIOTE.TASKS_SET
CC2 → PPI → GPIOTE.TASKS_CLR

and expected the CCs to keep firing. But since CC1/CC2 are one-shot, they only generate their events the first time the counter passes those values. They don’t reset or reload, so your LED toggles just once up and once down, then nothing.

One option could be that you could use the inbuilt PWM inside GRTC and configure the PWMCONFIG with the period and duty and then issue a TASKS_START, hardware should be able to now autotoggle CC0/CC1 for you yielding single periodic PWM channel with no CPU intervention.

One less confident trial that you can do is Use one PPI channel to link EVENTS_COMPARE[n] → TASKS_CLEAR. Use another PPI to link EVENTS_COMPARE[n] → GPIOTE.TASKS_SET/CLR and hoping that clearing the counter restarts the cycle and lets the same CC[n] fire again.

Otherwise I cannot think of anyway where we can do this without CPU involvement.