using serial port to debug on minix3

Surfing on minix news group, and I find it claim it has serial port output in kernel, but actually it is not complete.
UART, controller for controlling serial port ,game port and ...I didn;t got fimiliar with it.

Implemetation:
I write init_serialport(in kernel/kprintf.c) , it will be called in kernel main function if SERIAL_DEBUG is defined.
Then what kputc()(in kernel/kprintf.c) do is to write one char to register.

Thanks to
http://www.beyondlogic.org/serial/serial.htm#1