This callback allows detecting if there is a USB host connected to the CDC or not, in which case the stdout_tx should skip CDC TX writing and flushing or the system will block. Fixes issue #7820.
To match mp_sched_exception() and mp_sched_schedule(). Signed-off-by: Damien George <damien@micropython.org>
The REPL will be available on the USB serial port. Signed-off-by: Damien George <damien@micropython.org>