kernel.cpp

#ifdef __cplusplus
extern "C"{
#endif
#include <stddef.h>//we can use it as it does not use any platform-related api functions
#include <stdint.h>//include it to get int16_t and some integer types

/*   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;
}
uint8_t make_vgaentry(char c,uint8_t color){
    uint8_t c16=c;
    uint8_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=24;

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*) 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]);
}
void kernel_main()
{
    terminal_initialize();
    terminal_writestring("Welcome to TralahTek Operating System!");
    for(;;);
}
#ifdef __cplusplus
}
#endif