(1) The "standard" is pretty impossible as long as there are cheap microcontrollers and USB-UART adapters around. If your CPU runs at 4 MHz clock, you simply ca

(1) The "standard" is pretty impossible as long as there are cheap microcontrollers and USB-UART adapters around. If your CPU runs at 4 MHz clock, you simply cannot get 57600 baudrate going (without PLL, but 4MHz micro is not going to have it). But if you have embedded linux, you want it fast, at least 115200, maybe even 230400... But depending on the clock tree, your UART clock could be pretty low, so maybe 250000 baud is more realistic. But many cheaper adapters have problem with high speeds and/or non-standard rates, so if you expect your device to be serviced in the field with ad-hoc equipment, maybe go down to 57600 just to make sure? (2) The solution existed for a long time: get a logic analyzer or a scope, then look at the signal. This is pretty simple and very cheap, as sub-MHz logic analyzers are like $10 today. (3) That said, last time I had an unknown device I was too lazy to find my scope and connect it.. it was much easier to me to try a few bitrates using regular UART util output started to make sense, especially since it's often easy to tell if the bitrate is a bit off or way off.