org 0x7C00

bpb:
  jmp _startup ; 2 bytes
  nop ; 1 byte
.oem:
  db "OEM     "	; OEM
.bps:
  dw 0x200	; bytes per sector
.spc:
  db 1		; sectors per cluster
.rsectors:
  dw 2		; number of reserved sectors
.fats:
  db 2		; number of file allocation tables
.dirents:
  dw 2		; Number of directory entries
.sectors:
  dw 720	; total number of sectors
.mtd:		; media descriptor type
  db 0xFD	; 5.25-inch Double sided, 40 tracks per side, 9 sectors per track (360 KB)
.spfat:		; sectors per fat
  dw 0
.spt:
  dw 9		; sectors per track
.heads:
  dw 2		; number of heads
.hidsecs:
  dd 0		; number of hidden sectors
.lrgsectors:
  dd 0		; large sector count

times (0x3E - ($-$$)) nop

_startup:
  call printgeo
  mov ah, 0x08
  mov dl, 0x00
  int 0x13 ; required, QEMU detects 360kB as 1200kB with CHS 80 2 15
  jc .noadjust
  inc dh
  mov [bpb.heads], dh
  mov ax, cx
  and ax, 0x003F
  mov [bpb.spt], ax ; no adjustment because sectors are 1-indexed
  mov ax, cx
  xchg al, ah
  mov cl,6
  shr ah,cl
  inc ax ; convert from maximum number (0-based) to total number (1-based) of cylinders
  mul word [bpb.heads] ; number of tracks = number of cylinders * heads
  mul word [bpb.spt] ; number of sectors = number of tracks * sectors per track
  mov [bpb.sectors], ax
.noadjust:
  call printgeo
.end:
  hlt
  jmp .end

printgeo:
  mov ax, [bpb.heads]
  call print16
  mov ax, [bpb.spt]
  call print16
  mov ax, [bpb.sectors]
  call print16
  mov al, 0x0A
  call printc
  mov al, 0x0D
  call printc
  ret

; in	bx	sector number,
;	dl	drive number
;	ds:di	buffer
; out	al	error code,
;	carry set if error
loadblk:
  mov ax, bx
  div byte [bpb.spt]
  call print16
  ; Temp = LBA / (Sectors per Track)
  ; Sector = (LBA % (Sectors per Track)) + 1
  ; Head = Temp % (Number of Heads)
  ; Cylinder = Temp / (Number of Heads)

  ret

%include "print.asm"

times (0x1FE - ($-$$)) nop
dw 0xAA55