Zephyr Shell on custom board with nRF54L15

RE: Zephyr Shell on custom board with nRF54L15

CoussementStijn — Wed, 05 Nov 2025 15:16:28 GMT

Hi, Andreas,

Thanks for the response.

I needed to update de driver in the zephyr version I use,

I use the Nordic nRF Connect SDK v3.0.2. I will have to look for an update maybe...

RE: Zephyr Shell on custom board with nRF54L15

AHaug — Wed, 05 Nov 2025 14:37:22 GMT

Hi,

Since you're now using UART21 cross power domain (P2 instead of P1) you might be lacking configuring the UART to use constant latency, which was added in this commit https://github.com/nrfconnect/sdk-zephyr/commit/20db3ee4cf31537296f92c68cea67cb7707c8f3d#diff-81d3c13ab064092ea89aa9303da05ef054e95e157abb6bc26ad0f4a25d6d444f.

Could you let me know if you have enabled CONFIG_NRF_SYS_EVENT?

Edit: I see you've posted a comment just before me.

[quote user="Mysteryduck"]Wen I debug I do have a shell and I can see the logging. When I stop debugging it stops working. [/quote]

This strengthens my belief that you're not using constant latency for cross power domain use of UART21. When you examine this in a debugging session, this basically forces constant latency and thus that cross power domain use of peripherals works.. If you build with CONFIG_ASSERT=y you should probably get an assert for this: https://github.com/nrfconnect/sdk-zephyr/blob/c6dbf158a0b8c45beb78aa76412d99f60cd6467f/drivers/serial/uart_nrfx_uarte.c#L817C4-L817C84

Kind regards,
Andreas

RE: Zephyr Shell on custom board with nRF54L15

CoussementStijn — Wed, 05 Nov 2025 14:32:50 GMT

Wen I debug I do have a shell and I can see the logging. When I stop debugging it stops working.

I've used the following to investigate further:

const char c[] = "DEADBEEF\r\n";

dict_char_out_hex(uart_dev, (uint8_t *)c, sizeof(c) - 1);

uart_fifo_fill(uart_dev, (const uint8_t *)"UART initialized\r\n", 19);

where uart_poll_out is used to transmit the first string 'DEADBEEF' and that works while debugging and running solo.

The fifo fill does not work when not debugging.

The zephyr shell uses fifo_fill so it seems logic that I get the same reaction on that.

What do we need to configure to get uart_fifo_fill to work while not debugging?
It must be a timing issue i think as while debugging It runs slower and works as expected?

The strange thing is that no config changes can be found between the development kit and My own board.
Is there something I need to do to configure the DMA correctly or does the uart_fifo_fill not use DMA?