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

includes/io.h

@@ -1,4 +1,5 @@
 #ifndef IO_H
 #define IO_H
 void outb(unsigned short port, unsigned char data);
+unsigned char inb(unsigned short port);
 #endif

includes/kernel.h

@@ -1,9 +1,5 @@
 #ifndef KERNEL_H
 #define KERNEL_H
 
-void write_screen(unsigned int, char, unsigned char, unsigned char);
-void move(unsigned short);
-void draw_s(char*, unsigned char, unsigned char);
 int strlen(char*);
-void clear_screen(void);
 #endif

includes/serial.h

@@ -0,0 +1,23 @@
+#ifndef SERIAL_H
+#define SERIAL_H
+/* All the I/O ports are calculated relative to the data port. This is
+   because all serial ports have their ports in the same order but they
+   start at different values.
+*/
+
+#define COM1_PORT 						0x3F8
+
+#define SERIAL_DATA_PORT(base)			(base)
+#define SERIAL_FIFO_COMMAND_PORT(base) 	(base + 2)
+#define SERIAL_LINE_COMMAND_PORT(base) 	(base + 3)
+#define SERIAL_MODEM_COMMAND_PORT(base) (base + 4)
+#define SERIAL_LINE_STATUS_PORT(base) 	(base + 5)
+
+// Tells the serial port to expect the highest 8 bits on the data port first,
+// followed by the lowest 8 bits.
+#define SERIAL_LINE_ENABLE_DLAB 		0x80
+
+void set_serial_baud_rate(unsigned short, unsigned short);
+void configure_serial_line(unsigned short);
+int serial_transmit_fifo_empty(unsigned int);
+#endif