Using STTY with the USB-SWD

Answer

These instructions are intended for Linux or Macintosh OS. They may work using WSL, Cigwin, or other bash style terminals in Windows although this is untested. 

It may be desired to communicate with a device attached to the USB-SWD without terminal emulation, I.E. Picocom, Screen, Putty.  This can be useful for writing bash scripts, or if you're using Zephyr's "west flash" and would like a quick way to check your output. 

1. Verify you have the program "stty" available using the command "which stty", if this does not return a value you will need to install it.  Fortunately "stty" generally comes standard with Linux and MacOS.  
2. Identify your serial device.  This can be done using the command "dmesg -w" then connecting the USB-SWD.  You will see output like this (In Linux).

3. (Optional) Assign the device name to a variable, for example "DEVICE=/dev/ttyACM0".
4. Configure "stty" to talk with the device "stty -F $DEVICE 115200 -echo -echoe -echok"
5. To see output from the device execute "cat $DEVICE &".  This will send serial communication from the device to Linux's standard output.  The "&" is to run this program in the background.
6. Now press the reset button on the USB-SWD, you should see the output from your device.  In this example the Zephyr "Hello World" example has been flashed to a BT510. 

7. (Optional) if you would like to send commands back to the device you can use "echo" or add an argument to your shell, "foo() { echo -n -e "$1\r" > $DEVICE; }".  Now commands can be issued directly from the command line, for example "foo "my_command"" will send the string "my_command" to the device.