When I upload the .hex file and run it on the chip, it doesn't seem to be showing up as a USB device, though it is connectable by BLE (even though it doesn't seem to advertise correctly). When I debug it in GDB, it seems to always stop inside
jswrap_regexp routines, e.g.:
(gdb) monitor reset
target not halted
target nrf52.cpu was not halted when resume was requested
Program received signal SIGINT, Interrupt.
matchfound (txtIt=<optimized out>, info=...) at src/jswrap_regexp.c:57
57 jsvObjectSetChild(rmatch, "input", info.sourceStr);
Not sure if this is something wrong with my setup or it indeed is busy parsing regular expressions all the time for some reason. I will keep investigating - any pointers are appreciated!