My first assembly! Wrote a bootloader that just prints gibberish in colours. I tried to slow it down but couldn't figure out the interrupt handler stuff.

gistfile1.asm

use16
org 0x7c00

xor ax, ax
xor bx, bx
xor cx, cx
xor dx, dx
mov ds, ax
mov fs, ax

mov ss, ax
mov sp, 0x7bfe

mov ax, 0xb800
mov fs, ax

cli
mov [bx+0x20], word timer_handler
mov [bx+0x22], word 0

mov al, 0x36
out 0x43, al

%define divisor (1193180 / 50)
mov al, divisor & 0xff
out 0x40, al
mov al, (divisor >> 8) & 0xff
out 0x40, al

sti

disco:
  call rand
  mov [fs:bx], al
  mov [fs:bx + 1], ah
  add bx, 2
  cmp bx, 80 * 25 * 2
  mov eax, 0xffffffff
  call sleep
  jl disco

mov bx, 0
jmp disco

rand:
  rdtsc
  ret

tick:
  dd 0

sleep:
  mov [tick], eax
  .loop:
    mov eax, [tick]
    cmp eax, 0
    jg .loop
  ret

timer_handler:
  push eax
  mov eax, [tick]
  cmp eax, 0
  je .finish
  dec dword [tick]
  .finish:
    mov al, 0x20
    out 0x20, al
    pop eax
    iret

times 510-($-$$) db 0
db 0x55
db 0xaa