Recommended way to output 16 MHz clock on nRF54L15

[Kolesi]

Hi,

I need to output a continuous 16 MHz clock on a GPIO pin on the nRF54L15.

I first looked at the GRTC clock output, but since the fast clock is divided by (CLKFASTDIV × 2), the maximum output appears to be 8 MHz.

I also considered using TIMER + GPIOTE/DPPI with PPIB. However, P0/P1 are specified for a maximum GPIO speed of 8 MHz, while P2 supports higher speeds but does not have GPIOTE.

Is there a recommended hardware method to output a continuous 16 MHz clock on P2, or would this need to be generated in software,how? Is there another peripheral better suited for this use case?

Thanks!

[Turbo J]

You could try abusing the I²S peripherial, which can put out 16MHz as MCK.

No idea if it still works when not all signals are routed out to physical pins though.

[Kolesi]

Thanks, I2S MCK looks promising. Can the I2S MCK output be routed to a P2 pin on nRF54L15? My understanding is that I2S is not one of the peripherals normally allowed cross-domain access to P2 according to this Cross power-domain pins assignment. Would PSEL.MCK have a special clock-pin routing exception, or is MCK limited to P1?

[Kenneth]

Hello,

Unfortunately I don't see any way of achieving a stable 16MHz output.

The I2S peripheral is limited to using P1 and max 8 MHz:
https://docs.nordicsemi.com/r/bundle/ps_nrf54l15/page/i2s.html-topic#configuration 
https://docs.nordicsemi.com/r/bundle/ps_nrf54l15/page/i2s.html-master_clock_source_examples 
https://docs.nordicsemi.com/r/bundle/ps_nrf54l15/page/gpio.html-concept_port_capabilities 
https://docs.nordicsemi.com/r/bundle/ps_nrf54l15/page/chapters/pin.html-dedicated_pins 

Kenneth