pokeDtr

Opens driver's port, asserts DTR/RTS for holdMillis, and closes it again.

Exists because some firmware waits for a host before it will run: the nRF52 factory-erase image blocks in while (!Serial) before formatting, and Serial only becomes truthy once DTR is asserted. Deliberately does not go through createSerialConnection, which welds the assertion to a SerialInputOutputManager reader thread and a mandatory listener — there is no Meshtastic protocol on the other end here, just a blocked setup().