nRF5340 PWM limitations undocummented

RE: nRF5340 PWM limitations undocummented

Hieu — Mon, 10 Mar 2025 09:10:15 GMT

Thank you for the report. I am still unsure this is a hardware issue. I am also a little confused whether it's P1.01 or P0.31 that is working for you, but by default, both of them have purpose assigned on the nrf5340dk board:

P0.31 is LED3.

P1.01 is forwarded to network core to be used as an UART pin.

I don't see your DTS files reconfigure these nodes to any other pins, so most likely both of them still have their assignment. Among those, the pin forwarding and network core UART are automatically setup without any application code, so it makes sense that P1.01 is more likely to not work.

Furthermore, I see that both P0.31 and P1.01 are used in your project:
https://github.com/lheywang/Opale/blob/dev2/boards/topaze/DTSI/topaze-serial-gps.dtsi#L32
https://github.com/lheywang/Opale/blob/dev2/boards/topaze/DTSI/topaze-outputs.dtsi#L21

Not related, but I am not sure if using 0xffffffff to mark a pin unused works like you are having in the topaze-serial-gps.dtsi file. I haven't seen anywhere that suggest this is an approach.

RE: nRF5340 PWM limitations undocummented

l.heywang — Sat, 08 Mar 2025 08:45:19 GMT

Hi !

I won't be able to share that file, because I've "solved" the "issue" by myself a few days ago, and I don't have anymore this file.

If it may help, here is the source repo : https://github.com/lheywang/Opale/tree/dev2/boards/topaze/DTSI
The link point to the folder where I store each overlay, per peripherals (I found this method cleaner than all in one file). The base files are simply generated by the VScode Extension.

When I solved the "issue", ther where conflict effectively (that triggered a warning on the VScode extension), and solving them made channel 1 and 2 working. The channel 3 was remaining inactive until I placed it on the port 1, where I immediately started working.

And, since I've seen such limitations on the nRF54 series datasheet, I was thinking about signaling it, in case it was an error.

RE: nRF5340 PWM limitations undocummented

Hieu — Thu, 06 Mar 2025 14:02:36 GMT

Could you please share your compiled application zephyr.dts?

RE: nRF5340 PWM limitations undocummented

l.heywang — Wed, 05 Mar 2025 13:53:47 GMT

Hi !

It's not the case, since I'm using a custom board for the project (defined with the tool). So UART is actually on custom pins also.

And I checked ALL pins, since I got this situation before, a conflict, and the pins weren't working fine (logic, and this case is documented as unpredictable behavior on the documentation). So, I've listed all pins and their functions before writing here.

And the fact that I've seen this kind of limitations on other chips give me the hint that is more something documentation related rather than something linked to my software config.

RE: nRF5340 PWM limitations undocummented

Hieu — Wed, 05 Mar 2025 13:00:07 GMT

I think you might have a pin assignment conflict. By default, the nRF5340 DK has P1.01 used for UART TXD. Could you please check the DeviceTree to see if it is still being used for that purpose?

RE: nRF5340 PWM limitations undocummented

l.heywang — Tue, 04 Mar 2025 16:09:21 GMT

Hi !

I'm sorry for the comment that confused you. I'm working on a project with multiples persons (a friend and teachers). Furthermore, I own an nRF5340DK, and we have developed our custom PCB.

Since I'm the only one who own a DK, the unused comment is more for the others (In the meaning : Don't use it, it won't work since the pins aren't matched). I personally use the DK and a custom pinctrl overlay that align pins in a row, making it easier to plug scope and develop.

So yes, the "unused" overlay is, in fact, used.

And while I was developing on it, when the last channel was configured on port 1, it remains at a high state, ignoring any Zephyr API call to set the pulse length. And immediately after setting it to port 0 (same as the others), it started working.

RE: nRF5340 PWM limitations undocummented

Hieu — Mon, 03 Mar 2025 21:55:42 GMT

Hello Heywang,

I am a little confused with the description here. I understand that you posted two code snippets of a pinctrl node, with the first snippet shows something that works, while the second shows something that does not work.

However, the two snippets only differ in the pwm0_dk sub node, which has the comment that it is unused. The other sub node, pwm0_topaze, is the same in the two snippets.

Could you please clarify some more here?

Hieu