Fysetc Cheetah v1.2 boards require a special sequence to reset reliably.
This sequence works for me in all cases. Simpler sequences without
double reset did not work correctly. This is likely because of a weird
stateful circuitry for toggling the bootloader state.
Cheetah boards use RTS to configure bootloader triggering. By default,
pySerial sets RTS on connect, which unfortunately configures the board
to start the bootloader on reset.
Add a toggle for the RTS state to allow users to workaround. The RTS state
is set before the serial connection is opened, so there are no glitches.
Addresses #2026.
Signed-off-by: Grigori Goronzy <greg@chown.ath.cx>
0a20430e07