read_sector

readsector.s

; from http://www.mouseos.com/arch/processor_mode.html

;----------------------------------------------------------------------
; 
; read_sector(int sector, char *buf) - read one floppy sector(LBA mode)
; input:  di - sector
;         si - buf
;----------------------------------------------------------------------

read_sector:
    push cx
    push dx
    push es
    push ds
    pop es

    mov bx, si              ; data buffer
    mov ax, di             ; disk sector number

    ; LBA mode --> CHS mode
    ; cylinder = L / 36
    mov cl, 36
    div cl                  
    mov ch, al             ; ch = cylinder

    ; head = (L % 36) / 18
    mov al, ah
    xor ah, ah
    mov cl, 18
    div cl
    mov dh, al              ; dh = head

    ; sector = (L % 36) % 18 + 1
    mov cl, ah              ; cl = sector
    inc cl

    xor dl, dl             ; dl = drive

    ; ch - cylinder
    ; cl - sector ( 1 - 63)
    ; dh - head
    ; dl - drive number
    ; es:bx - data buffer 

    mov ax, 0x201
    int 0x13

    pop es
    pop dx
    pop cx

    ret