flash_writer.py
This flash writer is using the xmodem for firmware transfer on boards based on cxd56 chip (Ex. Spresense). This tool depends on the xmodem package (https://pypi.org/project/xmodem/).
For flashing the .spk image to the board please use:
$ tools/flash_writer.py -s -c /dev/ttyUSB0 -d -b 115200 -n nuttx.spk