org 0x7C00

cols: equ 80
rows: equ 30

main:
  mov ax, cs
  mov ds, ax
  mov es, ax
  mov ss, ax
  xor sp, sp

  mov ah, 0x42
  mov si, dap
  int 0x13

  mov ax, 0x0011
  int 0x10

  mov di, txtbuf
.loop:
  call sync
  xor ax, ax
  int 0x16
  stosb
  jmp .loop

hlt:
  hlt
  jmp hlt

sync:
  push ax
  push si
  push di
  push es
  mov si, txtbuf
  mov ax, 0xA000
  mov es, ax
  mov di, 0

  mov bx, font
  mov cx, rows
.loop:
  call charline
  loop .loop

  pop es
  pop di
  pop si
  pop ax
  ret

charline:
  push bx
  push cx
  mov cx, 8
.loop:
  call scanline
  call scanline
  inc bh
  loop .loop
  add si, cols
  pop cx
  pop bx
  ret

scanline:
  push si
  push cx
  mov cx, cols
.loop:
  lodsb
  mov bl, al
  mov al, [bx]
  stosb
  loop .loop
  pop cx
  pop si
  ret

dap:
  db 0x10
  db 1
  dw 20
  dw font, 0
  dq 1

times (510 - ($-$$)) nop

dw 0xAA55

font:
  incbin "cp437.bin"

txtbuf:
  times (rows * cols) db 0

end: