Porting Espruino to a new device

How you debug is going to depend on your board and processor. Ideally you'd have some kind of SWD/JTAG debugger that could could attach and use to step through your code, to check it's initialising properly.

Failing that, make main.c simply print 'Hello world' or something out of the serial port (without initialising Espruino at all). Then make sure you can get serial receive working (so it'll echo back the result) and work forwards from there - adding loads of print statements, trying to initialise Espruino and finally start looping and calling jsiIdle.

If you do need help it's possible I could do some consultancy work for you though.