OK, this is a little odd. I want to interface to an external device running at 9600 baud, which I can't change, while in the car. So, I set car_rate to 9600. Simple.
Except that it doesn't work.
After some testing, these are the symptoms:
Normal config.ini, no car rate modifiers, AC power. Serial port runs at 115200, all the serial commands to the player work correctly.
As above, with hijack forcing DC mode. No serial player control commands work, although they are echoed back to the terminal. Ctrl-c drops to a shell which works fine, at 115200. Attempting to connect at 4800, the car default, doesn't work or echo but simply gives garbage.
As above, with car_rate=9600. Same effect, doesn't work at either 4800 or 9600.
Powering the unit from the docking connector without hijack forcing DC mode produces the same result as case 2 and 3 above.
The unit has hijack v320 and Beta13 on it.
Experience is what you get just after it would have helped...