1 files changed, 126 insertions, 0 deletions
diff --git a/kernel/l0/kmain.c b/kernel/l0/kmain.c
new file mode 100644
index 0000000..9139856
--- /dev/null
+++ b/kernel/l0/kmain.c
@@ -0,0 +1,126 @@
+#if !defined(__cplusplus)
+#include <stdbool.h> /* C doesn't have booleans by default. */
+#endif
+#include <stddef.h>
+#include <stdint.h>
+ 
+/* Check if the compiler thinks if 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 "multiboot.h"
+ 
+extern void k_highhalf_addr;
+
+/* Hardware text mode color constants. */
+enum vga_color
+{
+	COLOR_BLACK = 0,
+	COLOR_BLUE = 1,
+	COLOR_GREEN = 2,
+	COLOR_CYAN = 3,
+	COLOR_RED = 4,
+	COLOR_MAGENTA = 5,
+	COLOR_BROWN = 6,
+	COLOR_LIGHT_GREY = 7,
+	COLOR_DARK_GREY = 8,
+	COLOR_LIGHT_BLUE = 9,
+	COLOR_LIGHT_GREEN = 10,
+	COLOR_LIGHT_CYAN = 11,
+	COLOR_LIGHT_RED = 12,
+	COLOR_LIGHT_MAGENTA = 13,
+	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;
+	terminal_color = make_color(COLOR_LIGHT_GREY, COLOR_BLACK);
+	terminal_buffer = (uint16_t*) (&k_highhalf_addr + 0xB8000);
+	for ( size_t y = 0; y < VGA_HEIGHT; y++ )
+	{
+		for ( size_t x = 0; x < VGA_WIDTH; x++ )
+		{
+			const size_t index = y * VGA_WIDTH + x;
+			terminal_buffer[index] = make_vgaentry(' ', terminal_color);
+		}
+	}
+}
+ 
+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 )
+	{
+		terminal_column = 0;
+		if ( ++terminal_row == VGA_HEIGHT )
+		{
+			terminal_row = 0;
+		}
+	}
+}
+ 
+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 kmain(struct multiboot_info_t *mbd, int32_t mb_magic)
+{
+	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");
+}