Added support for setting up a serial port. This first serial driver appears to only work correctly in QEMU.

kernel/serial.c

@@ -0,0 +1,59 @@
+#include "../includes/io.h"
+/* Sets the speed of the data being sent. The default speed of a serial port
+   is 115,200 bits/s. The argument is a divisor of that number, hence the resulting
+   speed becomes 115,200 / divisor bits/s.
+*/
+void set_serial_baud_rate(unsigned short com, unsigned short divisor){
+	outb(com + 3, 0x80);//SERIAL_LINE_ENABLE_DLAB);
+	
+	outb(com, (divisor >> 8) & 0x00FF);
+	
+	outb(com, divisor & 0x00FF);
+}
+
+void configure_serial_line(unsigned short com){
+
+	// Configuring the Line
+	/* d: 		Enables (1) or disables (0) DLAB
+	   b: 		Break if controls is enabled (1)
+	   parity: 	The number of parity bits to use
+	   s: 		The number of stop bits to use (0 = One Stop, 1 = 1.5 or 2 stops)
+	   dl: 		Describes the langth of the data
+	   
+	   Bit:		| 7 | 6 | 5 4 3 | 2 | 1 0 |
+	   Content: | d | b | parity| s | dl  |
+	   Value:	| 0 | 0 | 0 0 0 | 0 | 1 1 | = 0x03
+	*/
+	outb(com + 3, 0x03);
+	// Configuring the Buffers
+	/* lvl: How many bytes should be stored in the FIFO buffers
+	   bs: 	If the buffers should be 16 or 64 bytes large
+	   r:	Reserved
+	   dma:	How the serial port data should be accessed
+	   clt: Clear the transmission FIFO buffer
+	   clr: Clear the reciever FIFO buffer
+	   e:	If the FIFO bufffer should be enabled or not
+	   
+	   Bit:		| 7 6 | 5 | 4 | 3  | 2  | 1  | 0 |
+	   Content:	| lvl | bs| r | dma| clt| clr| e |
+	   Value: 	| 1 1 | 0 | 0 | 0  | 1  | 1  | 1 |
+	*/
+	outb(com + 2, 0xC7);	
+	// Confirgure the Modem
+	outb(com + 4, 0x03);
+}
+/* @return 0 if the FIFO is not empty
+		   1 if the FIFO is empty
+*/
+int serial_transmit_fifo_empty(unsigned int com){
+	// 0x20 = 0010 0000
+	return inb((com + 5) & 0x20);
+}
+
+void write_to_com(unsigned int com, char* msg){
+	for(int i = 0; msg[i] != '\0'; i++){
+		while(serial_transmit_fifo_empty(com) == 0);
+		
+		outb(com, (char) msg[i]);
+	}
+}