bootloader.img

boot.asm

.code16 # use 16 bits
.global main

main:
  mov $0x0002, %ax
  int $0x10 #set 80x25 text mode

  mov $0x0700, %ax
  mov $0x0f, %bh
  mov $0x184f, %dx
  xor %cx, %cx
  int $0x10 #clear screen (black background)
  jmp print_message


print_living_clock:

  mov $0x02, %ah
  mov $0x00, %bh
  mov $0x012a, %dx
  int $0x10 #reset cursor position

  # Read Timer
  mov $0x02, %ah
  int $0x1a
  
  # Print Hours  
  mov $0x0e, %ah
  mov %ch, %al
  int $0x10 

  # Print '/'
  mov $0x0e, %ah
  mov $0x2f, %al
  int $0x10

  # Print Minutes
  mov $0x0e, %ah
  mov %cl, %al
  int $0x10

  # Print '/'
  mov $0x0e, %ah
  mov $0x2f, %al
  int $0x10

  # Print Seconds 
  mov $0x0e, %ah
  mov %dh, %al
  int $0x10
  
  jmp print_living_clock

print_message:
  mov $0x02, %ah
  mov $0x00, %bh
  mov $0x0000, %dx
  int $0x10 # set cursor position

  mov $msg, %si # loads the address of msg into si
  mov $0x0001, %cx
  mov $0xe, %ah # loads 0xe (function number for int 0x10) into ah
  jmp print_char

print_message_2:
  mov $0x02, %ah
  mov $0x00, %bh
  mov $0x0100, %dx
  int $0x10 # set cursor position

  mov $msg2, %si # loads the address of msg into si
  mov $0x0002, %cx
  mov $0xe, %ah # loads 0xe (function number for int 0x10) into ah
  jmp print_char

print_message_3:
  mov $0x02, %ah
  mov $0x00, %bh
  mov $0x0200, %dx

  int $0x10 # set cursor position
  mov $msg3, %si # loads the address of msg into si
  mov $0x0003, %cx
  mov $0xe, %ah # loads 0xe (function number for int 0x10) into ah
  jmp print_char

print_char:
  mov $0x0e, %ah
  lodsb # loads the byte from the address in si into al and increments si
  cmp $0, %al # compares content in AL with zero
  je done # if al == 0, go to "done"
  mov $0xc0, %bl
  int $0x10 # prints the character in al to screen
  jmp print_char # repeat with next byte

done:
  cmp $0x0001, %cx
  je print_message_2
  
  cmp $0x0002, %cx
  je print_message_3

  cmp $0x0003, %cx
  je print_living_clock
  
end:
  hlt #Stops execution
msg: .asciz  "===================================================="
msg2: .asciz "           Your First Booting Program               "
msg3: .asciz "===================================================="

.fill 510-(.-init), 1, 0 # add zeroes to make it 510 bytes long
.word 0xaa55 # magic bytes that tell BIOS that this is bootable