PWM0 may be interfering with UART

RE: PWM0 may be interfering with UART

Naeem Maroof — Fri, 23 Feb 2024 15:03:22 GMT

Hi Nathan,

I haven't seen any such thing where SPI is interfering with the UART.

Which pins you are using on the DK, and how does your overlay look like? Also the proj.conf?

Will you be able to share a mini-project to demonstrate the issue?

RE: PWM0 may be interfering with UART

Nathan45 — Mon, 19 Feb 2024 16:26:53 GMT

No. Changing the drive strength ended up not doing anything. Sorry.

Do you have any experience with SPI interfering with UART?

Nathan

RE: PWM0 may be interfering with UART

hmolesworth — Sat, 17 Feb 2024 01:35:13 GMT

Did my suggestion help?: "If the Uart Tx output is S0S1 drive, try changing to H0H1 drive on Tx and see if that affects the magnitude of the spikes"

RE: PWM0 may be interfering with UART

Nathan45 — Fri, 16 Feb 2024 19:39:12 GMT

We've actually narrowed it down to UART and SPI. We'll be starting a new private ticket with our schematic details and such, but we were able to replicate the issue on the nRF52840 dev kit.

Steps to replicate:

1: Enable SPI 1 or 2 in zephyr

2: Use UARTE 1

3: Check UART output on a computer using terminal emulator or scope.

RE: PWM0 may be interfering with UART

hmolesworth — Fri, 16 Feb 2024 01:03:14 GMT

A circuit of the buzzer drive would be helpful; is the buzzer based on a piezo or coil? If the latter, notoriously noisy, is there a back emf clamp (diode, zener, etc)? Is the PWM drive single ended, half-bridge or full-bridge? "Precise period" sounds like PWM-driven interference, but it could also be one of the other peripherals. Adjacent pins and traces can show some crosstalk, but there is no known issue between PWM0 and UART0 I don't think. If the PWM pin or trace is close to the Uart pin or trace, try cutting one and hardwire the signal via a different route and pin and see if the interference changes. If the Uart Tx output is S0S1 drive, try changing to H0H1 drive on Tx and see if that affects the magnitude of the spikes. An oscilloscope trace showing the PWM vs Uart would be very helpful to determine any correlation.