Add communication via serial port

.gitignore

@@ -1,3 +1,5 @@
+*~
+*#
 *.iso
 isodir
 tools

kernel/kernel/kernel.c

@@ -1,8 +1,15 @@
+#define PORT 0x3f8
+
 #include <stdio.h>
 
 #include <kernel/tty.h>
+#include "serial.h"
 
 void kernel_main(void) {
 	terminal_initialize();
 	printf("Hello from OrionOS!\n");
+	printf("Testing serial\n");
+	init_serial();
+	write_serial('t');
+	printf("Test finished success!\n");
 }

kernel/kernel/serial.h

@@ -0,0 +1,67 @@
+#include <stdint.h>
+
+#define PORT 0x3f8          // COM1
+ 
+static int init_serial() {
+   outb(PORT + 1, 0x00);    // Disable all interrupts
+   outb(PORT + 3, 0x80);    // Enable DLAB (set baud rate divisor)
+   outb(PORT + 0, 0x03);    // Set divisor to 3 (lo byte) 38400 baud
+   outb(PORT + 1, 0x00);    //                  (hi byte)
+   outb(PORT + 3, 0x03);    // 8 bits, no parity, one stop bit
+   outb(PORT + 2, 0xC7);    // Enable FIFO, clear them, with 14-byte threshold
+   outb(PORT + 4, 0x0B);    // IRQs enabled, RTS/DSR set
+   outb(PORT + 4, 0x1E);    // Set in loopback mode, test the serial chip
+   outb(PORT + 0, 0xAE);    // Test serial chip (send byte 0xAE and check if serial returns same byte)
+ 
+   // Check if serial is faulty (i.e: not same byte as sent)
+   if(inb(PORT + 0) != 0xAE) {
+      return 1;
+   }
+ 
+   // If serial is not faulty set it in normal operation mode
+   // (not-loopback with IRQs enabled and OUT#1 and OUT#2 bits enabled)
+   outb(PORT + 4, 0x0F);
+   return 0;
+}
+
+int serial_received() {
+   return inb(PORT + 5) & 1;
+}
+ 
+char read_serial() {
+   while (serial_received() == 0);
+ 
+   return inb(PORT);
+}
+
+int is_transmit_empty() {
+   return inb(PORT + 5) & 0x20;
+}
+ 
+void write_serial(char a) {
+   while (is_transmit_empty() == 0);
+   
+   outb(PORT, a);
+}
+
+void serial_printf() {
+
+}
+
+inline void outb(uint16_t port, uint8_t val)
+{
+    asm volatile ( "outb %0, %1" : : "a"(val), "Nd"(port) );
+    /* There's an outb %al, $imm8  encoding, for compile-time constant port numbers that fit in 8b.  (N constraint).
+     * Wider immediate constants would be truncated at assemble-time (e.g. "i" constraint).
+     * The  outb  %al, %dx  encoding is the only option for all other cases.
+     * %1 expands to %dx because  port  is a uint16_t.  %w1 could be used if we had the port number a wider C type */
+}
+
+inline int inb(int port)
+{
+    uint8_t ret;
+    asm volatile ( "inb %1, %0"
+                   : "=a"(ret)
+                   : "Nd"(port) );
+    return ret;
+}