Scott, after "lock()" here, should I disable irq4 and rx, and enable tx? 

		lock();
			/* ready to use 3f9,3f8 as divisor */
			out_byte(tty->port+LCR, 0x80); 
			out_byte(tty->port+DIVH, 0x00);
			/* divisor = 12 ===> 9600 bauds */
			out_byte(tty->port+DIVL, 12); 


			/**** term 9600 /dev/ttyS0: 
			8 bits/char, no parity ****/ 
			out_byte(tty->port+LCR, 0x03); 

			/* clear lingering interrupts 
			by reading status and data regs */
			in_byte(tty->port+LSR);
			in_byte(tty->port+MSR);
			in_byte(tty->port+DATA);

			/*write to MSR and IER*/
			/* 1011 ==> IRQ4, RTS, DTR on */
			out_byte(tty->port+MCR, 0x0B); 
			/* Enable Rx interrupt, Tx off */
			out_byte(tty->port+IER, 0x01); 
		unlock();