Basic serial driver

Makefile

@@ -8,9 +8,11 @@ kernel.o: kernel.c
 	tcc -m32 -c kernel.c
 vga.o: vga.c
 	tcc -m32 -c vga.c
+serial.o: serial.c
+	tcc -m32 -c serial.c
 
-kernel-i386.elf: kernel.o start32.o vga.o
+kernel-i386.elf: kernel.o start32.o vga.o serial.o
-	tcc -m32 -nostdlib -Wl,-Ttext,0x100000 start32.o kernel.o vga.o -o kernel-i386.elf
+	tcc -m32 -nostdlib -Wl,-Ttext,0x100000 start32.o kernel.o vga.o serial.o -o kernel-i386.elf
 
 qemu-multiboot: kernel-i386.elf
 	qemu-system-i386 -kernel kernel-i386.elf -serial stdio

kernel.c

@@ -1,9 +1,15 @@
 #include "multiboot.h"
 #include "vga.h"
+#include "serial.h"
 
 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;
+}
 
 char* itoa(int value, int base) {
     char* result;
@@ -41,6 +47,14 @@ void kmain (unsigned int mbootmagick, multiboot_info_t* mbootinfo) {
     vga_init(VGA_COLOR_BLACK, VGA_COLOR_GRAY);
 
     vga_write_line("=== KoalemOS ===");
+
+    if (serial_init() > 0) {
+        vga_write_line_color("Serial initialization failed", VGA_COLOR_BLACK,
+                             VGA_COLOR_ORANGE);
+    } else {
+        vga_write_line("\nInitialized serial.");
+        serial_write_string("\n=== KoalemOS ===\n");
+    }
     vga_write("Checking multiboot loader: ");
 
     // Check multiboot header
@@ -56,23 +70,30 @@ void kmain (unsigned int mbootmagick, multiboot_info_t* mbootinfo) {
     vga_write("\nMultiboot flags: ");
     vga_write(itoa(mbootinfo->flags, 2));
 
-    // Check videomode
+    serial_write_string("\nMultiboot flags: ");
-    vga_write("\nVideomode: ");
+    serial_write_string(itoa(mbootinfo->flags, 2));
 
+    // Check videomode
     if (mbootinfo->flags & MULTIBOOT_INFO_VBE_INFO) {
-        vga_write("VBE 0x");
+        vga_write("\nVBE Mode: 0x");
         vga_write(itoa(mbootinfo->vbe_mode, 16));
-    } else if (mbootinfo->flags & MULTIBOOT_INFO_FRAMEBUFFER_INFO) {
+        serial_write_string("\nVBE Mode: 0x");
-        vga_write("Framebuffer");
+        serial_write_string(itoa(mbootinfo->vbe_mode, 16));
-        vga_write("\nVideo address: 0x");
+    }
+    if (mbootinfo->flags & MULTIBOOT_INFO_FRAMEBUFFER_INFO) {
+        vga_write("\nFramebuffer: ");
+        vga_write("address: 0x");
         vga_write(itoa(mbootinfo->framebuffer_addr, 16));
-        unsigned long long *vmem = &mbootinfo->framebuffer_addr;
+        serial_write_string("\nFramebuffer: ");
+        serial_write_string("address: 0x");
+        serial_write_string(itoa(mbootinfo->framebuffer_addr, 16));
+        unsigned long *vmem = &mbootinfo->framebuffer_addr;
         *vmem = 0xff00ff;
 
     } else {
-        vga_write_color("Not available", VGA_COLOR_BLACK, VGA_COLOR_RED);
+        vga_write_color("Info not available", VGA_COLOR_BLACK, VGA_COLOR_RED);
+        serial_write_string("Info not available");
         return;
     }
-
     vga_write_line("\nExecution finished, halting...");
 }

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++;
+    }
+
+}

serial.h

@@ -0,0 +1,7 @@
+#ifndef HEADER_SERIAL
+#define HEADER_SERIAL
+
+int serial_init(void);
+void serial_write_string(const char* text);
+
+#endif