; Code related to memory segment from 0xFFFF0 - 0x10FFEF

; Check if 0000:0000 and FFFF:0010 point to the same memory
; ZF=1 when A20 disabled and HMA unusable
; ZF=0 when A20 enabled
a20_enabled:
  mov ax, 0x0000
  mov ds, ax
  mov si, ax
  mov ax, 0xFFFF
  mov di, 0x0010
  mov cx, 0x0200
  repe cmpsw
  ret

; Relocate kernel code to HMA
hma_relocate:
  call a20_enabled
  ; TODO: talk to hw to enable a20
  jz .end
  mov ax, cs
  mov ds, ax
  mov si, 0x0010
  mov ax, 0xFFFF
  mov es, ax ; new code segment
  mov ss, ax ; new stack segment
  mov di, 0x0010
  mov cx, 0x7FF8 ; 0xFFF0 divided by 2
  repe movsw
  jmp 0xFFFF:.end
.end:
  ret