Basic serial driver

serial.c

@@ -0,0 +1,49 @@
+#include "serial.h"
+#define PORT 0x3f8 // COM1
+
+static inline void outb(unsigned short port, unsigned char val) {
+  asm volatile ("outb %0, %1" : : "a"(val), "Nd"(port) : "memory");
+}
+static inline unsigned char inb(unsigned short port) {
+  unsigned char ret;
+  asm volatile("inb %1, %0" : "=a"(ret) : "Nd"(port) : "memory");
+  return ret;
+}
+
+int serial_init() {
+  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;
+}
+static int serial_is_transmit_empty() { return inb(PORT + 5) & 0x20; }
+
+static void serial_write_char(char chr) {
+  while (serial_is_transmit_empty() == 0);
+  outb(PORT, chr);
+}
+
+void serial_write_string(const char* text) {
+    int i = 0;
+    while(text[i]) {
+        serial_write_char(text[i]);
+        i++;
+    }
+
+}