Add: init serial + getting text out of it

src/io/serial.c

@@ -0,0 +1,59 @@
+#include "../kernel.h"
+
+void outb(int port, unsigned char data)
+{
+    __asm__ __volatile__("outb %%al, %%dx" :: "a" (data),"d" (port));
+}
+
+unsigned char inb(int port)
+{
+    unsigned char data = 0;
+    __asm__ __volatile__("inb %%dx, %%al" : "=a" (data) : "d" (port));
+    return data;
+}
+
+// COM1
+#define PORT 0x3F8
+
+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)
+
+    if (inb(PORT) != 0xAE)
+    {
+        return -EIO;
+    }
+
+    // Set normal operation mode
+    outb(PORT + 4, 0x0F);
+    return 0;
+}
+
+static int is_transmit_empty()
+{
+    return inb(PORT + 5) & 0x20;
+}
+
+void write_serial(char c)
+{
+    while (!is_transmit_empty()); // wait for free spot
+    outb(PORT, c);
+}
+
+void serial_kputs(const char* str)
+{
+    unsigned int i=0;
+    while (str[i])
+    {
+        write_serial(str[i]);
+        i++;
+    }
+}

src/io/serial.h

@@ -0,0 +1,10 @@
+#ifndef SERIAL_H
+#define SERIAL_H
+
+void outb(int port, unsigned char data);
+unsigned char inb(int port);
+
+int serial_init();
+void serial_kputs(const char* str);
+
+#endif

src/kernel.h

@@ -3,7 +3,8 @@
 
 enum ErrorCodes
 {
-	ENOMEM
+	ENOMEM,
+	EIO
 };
 
 #endif

src/kmain.c

@@ -3,6 +3,7 @@
 #include <limine.h>
 #include "io/term.h"
 #include "io/printf.h"
+#include "io/serial.h"
 
 // Limine version used
 __attribute__((used, section(".limine_requests")))
@@ -111,6 +112,10 @@ void kmain()
 
 	if (term_init()) hcf();
 
+	if (serial_init()) kputs("kernel: serial: error: Cannot init serial communication!");
+	
+	serial_kputs("\n\nkernel: serial: Hello, world from serial!");
+
 	// Draw something
 	printf("%s, %s!", "Hello", "world");