Instructions
Probably need to install first
rustup target add thumbv7em-none-eabihf
cargo build --release
check compiled binary file size. It should be quite large, e.g.
ll target/thumbv7em-none-eabihf/release/app
-rwxrwxr-x 2 knoppix knoppix 1107216 Jul 4 22:25 target/thumbv7em-none-eabihf/release/app*
in one console window open openocd
openocd -f openocd.cfg
in second window upload code into microcontroller
arm-none-eabi-gdb -x openocd.gdb