bootloader.x

asm{
    "[bits 16]",
    "[org 0x7c00]"
}
//global character to print
char pchar;pchar=0;

char x_pos,y_pos;
//enter key
char enter_key;enter_key=0x1c;
///global array
char vbuffer[32];
//bootloader starting point
void start(){
    char ch;
    clear_screen();
    //print each alphabet from A to Z
    for(ch='A';ch<='Z';ch++){
        pchar=ch;
        print_char();
    }
    //goto nextline
    goto_newline();
    //assign type:characters to array vbuffer
    vbuffer[0]='T';
    vbuffer[1]='y';
    vbuffer[2]='p';
    vbuffer[3]='e';
    vbuffer[4]=':';
    vbuffer[5]=0;
    //print whole array
    print_array();
    goto_newline();goto_newline();
    //test the input
    input_test();
}
//print array until 0 found in vbuffer
void print_array(){
    char i;
    for(i=0;i<32;i++){
        pchar=vbuffer[i];
        if(pchar==0){
            break;
        }else{
            print_char();
        }
    }
}
/*get key by callling read_key()
if key is enter_key then goto nextline
    otherwise orint that char
    */
void input_test(){
    short key;
    char key_code;
    while(1){
        key=read_key();
        pchar=(char)key;
        key=key&240;
        key_code=key;
        if(key_code == enter_key){
      goto_newline();
    }else{
      print_char();
    }
    }
}
void goto_newline()
{
  y_pos++;
  x_pos = 0;
  gotoxy();
}
//call BIOS interrupt to read key
//result is always in eax register, so no return statement
short read_key()
{
  asm{
    "\tmov ax,0x00",
    "\tint 0x16"
  }
}
//BIOS interrupt to goto x,y pos
void gotoxy()
{
  asm{    "\tmov ah, 0x02",
    "\tmov bh, 0x00",
    "\tmov dl, %" ["=m"(x_pos):],
    "\tmov dh, %" ["=m"(y_pos):],
    "\tint 0x10"
  }
}
//print character using BIOS interrupt
void print_char()
{
  asm{
    "\txor bx, bx",
    "\tmov bl, 10",
    "\tmov al, %" ["=m"(pchar):],
    "\tmov ah, 0x0E",
    "\tint 0x10"
  }
}
void clear_screen()
{
  asm{
      "\tmov al, 2",
      "\tmov ah, 0",
      "\tint 0x10"
  }
}
//define bootloader signature
asm{
  "times (510 - ($ - $$)) db 0x00",
  "dw 0xAA55"
}