When a build target has a corresponding .flash.py script, that script can be run to flash the target to an attached device.
This is really just a wrapper around ${PLATFORM}_firmware_utils.py with built-in argument defaults, so that it can typically be run with no arguments. You can however supply additional command line arguments to override or supplement the defaults, for example to select a specific connected device. In particular, ${TARGET}.flash.py --help lists the available arguments.
These scripts invoking flashing tools for the particular platform with a more-or-less uniform interface. The core set of command line options is
--erase Erase device --application FILE Flash an image --verify_application Verify the image after flashing --reset Reset device after flashing
Running ${PLATFORM}_firmware_utils.py --help will show the complete list of available command line options for that platform.
Normally this is done automatically for a suitable GN build target.
The script gen_flashing_script.py builds a ${TARGET}.flash.py wrapper script to invoke the firmware utils with a particular set of argument defaults. Run this as
gen_flashing_script.py ${PLATFORM} --outputfilename [argument ...]
The arguments are the same as those of ${PLATFORM}_firmware_utils.py. Some platforms may have additional options, e.g. to obtain additional values from a configuration file. Use gen_flashing_script.py ${PLATFORM} --help to list all options for a particular platform.