add UART init code and send every char to UART

messages.asm

@@ -11,6 +11,15 @@ PIT_CH2_DATA_PORT equ 0x42	; PIT channel 2 data port
 ;; see http://www.ctyme.com/intr/int-10.htm for interrupts
 
 start:
+
+mov sp, 0x2000	; initialise stack pointer
+
+;; initialise serial port
+mov ah, 0x0		; initialise UART
+mov al, 0b111_00_0_11	; baud 9600, no parity, 1 stop bit, 8 data bits
+mov dx, 0x0		; COM1
+int 0x14
+
 ;; Use color mode
 mov	ax, VIDEO_MODE
 int	10h
@@ -31,12 +40,13 @@ mov dh, HEIGHT	; row (bottommost row)
 mov dl, 0x00	; col (leftmost col)
 int 0x10
 
-mov sp, 0x2000	; initialise stack pointer
-
 .loop:
-	mov ah, 0x00	; Read a character
+	;; read a character, ASCII in al
+	mov ah, 0x00	; Read character
 	int 0x16
 
+	call UART_send_char
+
 	cmp al, 0x08 	; backspace
 	je change_color_mode
 
@@ -52,6 +62,18 @@ mov sp, 0x2000	; initialise stack pointer
 	call newline
 	jmp .loop
 
+;; Prints a character in al to the serial port
+;;
+;; CLOBBERS
+;; - ax
+;; - dx
+UART_send_char:
+	mov ah, 0x01	; transmit character
+	mov dx, 0x0	; COM1
+	int 0x14
+
+	ret
+
 ;; Update the color_mode variable with a byte from the keyboard
 ;;
 ;; CLOBBERS