; Load a sector from drive.
; IN    DX:AX   sector number
;	BP	ptr to BPB
drive_read:
  push ax
  push cx
  push dx
  push bx
  push si

  mov cx, dx
  or cx, ax
  jz .fast

  div word [bp+13] ; ax:temp     = (lba / spt)
  inc dx           ; dx:sector   = (lba % spt) + 1
  mov cl, dl       ; sector number

  div word [bp+15] ; ax:cylinder = (tmp / heads)
                   ; dx:head     = (tmp % heads)
  mov ch, al       ; cylinder number
  mov dh, dl       ; head number
  mov si, 5        ; retry count
.try:
  mov dl, [bp+(bpb_size-1)] ; drive number
  mov bx, diskbuf
  mov ax, 0x0201
  int 0x13
.giveup:
  pop si
  pop bx
  pop dx
  pop cx
  pop ax
  ret
.fast: ; fast lane for boot sector
  inc cl
  jmp .try
.fail:
  ; reset disk
  mov ah, 0x00
  int 0x13
  ; loop with si
  dec si
  test si, si
  jnz .try
  stc
  jmp .giveup