Useful for navio2 or px4_raspberrypi when attaching a secondary (UART) GPS through one of the USB ports; the default navio2 onboard GPS is running on spi.
Example usage:
gps start -d /dev/spidev0.0 -i spi -e /dev/ttyACM0 -j uart -p ubx
UART is the primary interface for telemetry radio: https://docs.emlid.com/navio2/ardupilot/hardware-setup/#uart-radio
Check first if /dev/ttyUSB0 exists (https://docs.emlid.com/navio2/ardupilot/hardware-setup/#usb-radio); if not, fall back to configuring over UART (/dev/ttyAMA0).
Use stricter check for character special file (-c) rather than just file (-f).
'console=serial0,115200' needs to be removed from /cmdline.txt as additional configuration step. This should be documented in the Navio2 section of docs.px4.io. Presumably, this is already performed as part of the Raspberry Pi OS prebuilt image Emlid spins.
Adam Blazczak