Make serial work more reliably

src/asm.c

-/*
-  asm.c contains x86 specific functions for executing low level code
-*/
-
-#include "asm.h"
-
-// Wrapper for outb
-// Stolen from http://wiki.osdev.org/Inline_Assembly/Examples
-static inline void outb(uint16_t port, uint8_t val) {
-    asm volatile ("outb %0, %1" : : "a"(val), "Nd"(port));
-}
-
-// Wrapper for inb
-static inline uint8_t inb(uint16_t port) {
-    uint8_t ret;
-    asm volatile ("inb %1, %0" : "=a"(ret) : "Nd"(port));
-    return ret;
-}

src/asm.h

 /*
-  asm.h exports archatecture specific functions for hardware interaction
+  asm.h contains x86 specific functions for executing low level code
 */
 
+#pragma once
 #include <stdint.h>
 
-// Functions for reading and writing to/from x86 IO ports
-static inline void outb(uint16_t port, uint8_t val);
-static inline uint8_t inb(uint16_t port);
+// Wrapper for outb
+// Stolen from http://wiki.osdev.org/Inline_Assembly/Examples
+inline void outb(uint16_t port, uint8_t val) {
+    asm volatile ("outb %0, %1" : : "a"(val), "Nd"(port));
+}
+
+// Wrapper for inb
+inline uint8_t inb(uint16_t port) {
+    uint8_t ret;
+    asm volatile ("inb %1, %0" : "=a"(ret) : "Nd"(port));
+    return ret;
+}

src/kern.c

@@ -3,19 +3,19 @@
 #endif
 #include <stddef.h>
 #include <stdint.h>
- 
+
 /* Check if the compiler thinks we are targeting the wrong operating system. */
 #if defined(__linux__)
 #error "You are not using a cross-compiler, you will most certainly run into trouble"
 #endif
- 
+
 /* This tutorial will only work for the 32-bit ix86 targets. */
 #if !defined(__i386__)
 #error "This tutorial needs to be compiled with a ix86-elf compiler"
 #endif
 
 #include "serial.h"
- 
+
 /* Hardware text mode color constants. */
 enum vga_color {
 	COLOR_BLACK = 0,
@@ -35,32 +35,32 @@ enum vga_color {
 	COLOR_LIGHT_BROWN = 14,
 	COLOR_WHITE = 15,
 };
- 
+
 uint8_t make_color(enum vga_color fg, enum vga_color bg) {
 	return fg | bg << 4;
 }
- 
+
 uint16_t make_vgaentry(char c, uint8_t color) {
 	uint16_t c16 = c;
 	uint16_t color16 = color;
 	return c16 | color16 << 8;
 }
- 
+
 size_t strlen(const char* str) {
 	size_t ret = 0;
 	while ( str[ret] != 0 )
 		ret++;
 	return ret;
 }
- 
+
 static const size_t VGA_WIDTH = 80;
 static const size_t VGA_HEIGHT = 25;
- 
+
 size_t terminal_row;
 size_t terminal_column;
 uint8_t terminal_color;
 uint16_t* terminal_buffer;
- 
+
 void terminal_initialize() {
 	terminal_row = 0;
 	terminal_column = 0;
@@ -73,16 +73,16 @@ void terminal_initialize() {
 		}
 	}
 }
- 
+
 void terminal_setcolor(uint8_t color) {
 	terminal_color = color;
 }
- 
+
 void terminal_putentryat(char c, uint8_t color, size_t x, size_t y) {
 	const size_t index = y * VGA_WIDTH + x;
 	terminal_buffer[index] = make_vgaentry(c, color);
 }
- 
+
 void terminal_putchar(char c) {
 	terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
 	if (++terminal_column == VGA_WIDTH) {
@@ -92,25 +92,26 @@ void terminal_putchar(char c) {
 		}
 	}
 }
- 
+
 void terminal_writestring(const char* data) {
 	size_t datalen = strlen(data);
 	for (size_t i = 0; i < datalen; i++)
 		terminal_putchar(data[i]);
 }
- 
+
 #if defined(__cplusplus)
 extern "C" /* Use C linkage for kernel_main. */
 #endif
 void kernel_main() {
 	/* Initialize terminal interface */
 	terminal_initialize();
- 
+
 	/* Since there is no support for newlines in terminal_putchar
          * yet, '\n' will produce some VGA specific character instead.
          * This is normal.
          */
-	terminal_writestring("Hello, kernel World!\n");
     serial_init();
-    serial_writestring("Hello, kernel World!\n");    
+    serial_writestring("First Serial Test!\n");
+    terminal_writestring("Hello, kernel World!\n");
+    serial_writestring("Second Serial Test\n");
 }

src/makefile

@@ -6,3 +6,4 @@ all:
 	$C -T linker.ld -o myos.bin -ffreestanding -O2 -nostdlib *.o -lgcc
 
 clean:
+	rm *.o *.bin

src/serial.c

@@ -27,7 +27,7 @@ void serial_writechar(char a) {
 }
 
 void serial_writestring(char* s) {
-    while (s) {
+    while (*s) {
         serial_writechar(*s);
         s++;
     }