Configuration can be a bit of a pain for using the serial port on the raspberry pi with ubuntu. You can use either for communications, but if you've followed
the instructions, you most likely will be using `/dev/serial1`.

Difference between `/dev/serial0` and `/dev/serial1`:
- `/dev/serial0` maps to `/dev/ttyS0`, which handles serial communication through a software "mini-UART" implementation.
- `/dev/serial1` maps to `/dev/ttyAMA0`, which handles serial communication through a hardware PL011 UART implementation.
- The PL011 UART (UART0) is a full-featured universal asynchronous receiver/transmitter for serial communication
- the mini-UART (UART1) has a reduced set of features
- On the RPi4, the PL011 UART is also connected to the bluetooth controller.
<!-- - On the RPi4, the mini-UART is primary, and the PL011 UART is secondary -->

See [this discussion](https://www.engineersgarage.com/microcontroller-projects/articles-raspberry-pi-serial-communication-uart-protocol-serial-linux-devices/) and [this discussion](https://spellfoundry.com/2016/05/29/configuring-gpio-serial-port-raspbian-jessie-including-pi-3-4/) for more information.

- when using `/dev/serial0` for serial communications instead of `/dev/serial1`, you're using a less capable communications device. For whatever reason, this worked under ubuntu 18.04, but but seems to have a lot of trouble under ubuntu 20.04. So it's best to use `/dev/serial1`.
- However, `/dev/serial1` is also connected to the bluetooth controller, so we need to disable bluetooth. This is why we use the `dtoverlay=disable-bt` overlay in config.txt (see [rpi.md](rpi.md))
- We also need to remove `console=serial0,115200` from cmdline.txt, because it also seems to prevent the operation of `serial1` for serial comms.

To find out which one you should be using, run [the test script](../scripts/roboclawtest.py). If you want to use `serial0` instead of `serial1`, you must change
the default in the [config yaml](../osr_bringup/config/roboclaw_params.yaml).