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;----------------------------------------------;
;------------- read_sector --------------------;
;----------------------------------------------;
;------ es = buffer address -------------------;
;------ bx = buffer offset  -------------------;
;------ cx = sector to read -------------------;
;------ dl = drive          -------------------;
;----------------------------------------------;
;------ for 1.44MB Floppys 80 Sectors ---------;
;----------------------------------------------;
read_sector:
   pusha
   push bx         ; save buffer offset

   ; compute the sector number:   sector_number%sectors_per_track + 1
   mov ax, cx      ; ax = sector number
   mov bl, 18      ; bl = number of sectors per track
   div bl         ; al = ax / bl
   mov cl, ah      ; cl = real sector number (cl is used by int 13)
   add cl, 1

   ; compute the head number: (sector_number/sector_per_track) just in ax mod number_of_heads
   ; and the track number:    (sector_number/sector_per_track) / number_of_heads

   xor ah, ah      ; del the rest of the div before
   mov bl, 2      ; bl = number of heads
   div bl         ; ah = rest of ( ax / bx ), al = ax / bx
   mov ch, al      ; ch = number of track
   mov dh, ah      ; dh = the head number (dh is used by int 13)

   pop bx         ; restore the buffer offset

   mov ax, cx      ; save cx in ax
   mov cx, 5      ; try to read the sector 5 times ;!!! overwrite the num of track and num of sec
   
    read_sector_next_try:
   pusha

   mov cx, ax      ; restore cx

   mov ah, 0x02      ; function number 2 (read from disk)
   mov al, 0x01       ; number of sectors to read
   int 0x13

   jnc load_ok      ; if all is ok return
   
   popa
   loop read_sector_next_try; else try once again if there is an error
   jmp error      ; if cx = 0 and the read operation always failed, halt

load_ok:
   popa
   popa
   ret