what are the possible RS232 baud rates on a SBC BL2100?

There is no set list of possible baud rates when opening a serial port. Instead you can check the return code when using serXopen (with X standing for the particular serial port).

For example, a return of 1 when using

rc = serDopen(115200);

means that you were able to open the serial port at 115200 baud.

A return of 0 means that it was not successfully opened at that baud rate. I believe this is within/without a 5% tolerance.

The baud rate is set from 2 timers and the 2.21184 MHz clock. All possible baud rates would be 22118400 / x / y where x and y can range from 1 to 256. Only certain combinations end up as whole number baud rates. i.e dividing by 36 and 64 give s 9600 baud. So does 72 and 32.