I have the following hardware/software setup:
- Sferalabs StratoPi Base (Raspberry Pi 3B+ with a HAT for RS232/485)
- Distro built with Yocto and meta-raspberrypi on thud branch
I want to be able to free the GPIO 14/15 (TX/RX pins for UART) because the HAT needs these pins for RS232/485 communication.
As soon as I stop using U-Boot, the StratoPi device works and I can communicate with the devices on the RS485 bus. But I can't free the UART from getting used by Linux/U-Boot if I use U-Boot.
Does someone know how to make the UART pins available to the HAT?
I've tried to:
- Remove all references to ttyAMA0 in cmdline.txt and in /etc/inittab
- Patch U-Boot like here : https://stackoverflow.com/a/64583919/9077458
- Use pi3-disable-bt overlay
None of them worked for me.