The problem with serial data is finding the start / stop bits. If the serial bits are a continuous stream, it can be surprisingly difficult.
Well is it really? Using the pulseIn() command measuring the first low to high pulse width it sees will either capture the width of the first start bit width or any valid zero data bit width if the stream is already active. A start bit and a data bit have the same width at any given baud rate.
That should be the only info needed to then calculate or lookup the value to then use in the serial.begin function? The only hard decision I see is if to just hang waiting or put a timeout value to signify that it's still waiting for a first character to arrive, possible blink a led while waiting. I think it's simple using the already created pulseIn() function.
What am I missing?
Lefty