Proxy for connecting an ADX touchscreen to a real serial port.

Why is this needed?

Despite "talking" at 9600 baud, the ADX microcontroller presents as a USB-CDC serial port. No real RS-232 communications ever happen, so the baud rate is a meaningless configuration parameter on the port. It is able to send data at USB speeds and ignore the baud rate. A simple solution to this problem would be to simply run socat or similar to bridge the two ports, but this breaks down due to one end sending data at a much higher rate than 9600 baud. An additional quirk I've noticed is that the ADX seems to expect to recieve a whole command in a single write() call (which I assume usually maps to one transaction on the bus) and does not seem to perform buffering to handle messages that may be split across multiple writes.

What does this thing do?

This means we need to do the following to get this to work:

• Buffer commands from serial to send to the ADX, ensuring that a single command is sent per write() call.
• When the game requests the touchscreen to enter streaming mode, consume the touch updates at USB speeds.
• Send the most up-to-date touch update over serial as fast as we can