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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

   mov ax, cx      ; ax = sector number
   mov bx, 18      ; bx = number of sectors per track
   div bx         ; al = ax / bx
   mov cl, al      ; cl = real sector number (cl is used by int 13)

   ; 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 bx, 2      ; bx = number of heads
   div bx         ; 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

Code: Select all

   mov bx, 2      ; bx = number of heads
   div bx         ; 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)

Code: Select all

trans_address:      
; _________________________________________________________________
;/Translates Logical sector in AX to Physical sector,head,cylinder   \
;Input:- the LBA address in the AX reg      *
;Output:- cl=sector,ch=cylinder,dh=head      *
;Formula:-                                    *
; HPC = Number of heads/cylinder         *
; SPT = sectors/track            *
; Cylinder = (LBA / SPT) / HPC         *
; Head = (LBA / SPT) mod HPC                         *
; Sector = (LBA mod SPT) + 1         *
; Registers Affected:- AX,CX,DX         *
;------------------------------------------------------*
xor   dx,dx      ; clear out DX reg         *
div   word [SECTS_PER_TRK]   ; divide AX by SPT         *
inc    dl      ; increment dl to get sector address   *
mov   cl,dl         ; get sector value         *
xor   dx,dx         ; clear DX reg            *
div   word [HEADS]      ;                *
mov   ch,al         ; get cylinder value         *
mov   dh,dl         ; get head value         *
retn            ; all values obtained now      *
;\_______________________________________________/

Code: Select all

pushad

   mov ax, 72  ;cx      ; ax = sector number
   mov dx,0x00
   mov bx, 18      ; bx = number of sectors per track
   div bl         ; al = ax / bx
   mov cl, al      ; cl = real sector number (cl is used by int 13)

   ; 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
   call  write_hex32
   mov bx, 2      ; bx = number of heads
   div bl         ; ah = rest of ( ax / bx ), al = ax / bx
   call  write_hex32
   mov   ax,dx
   call  write_hex32

popad
;--------------------------------------------------------------
   mov ax, 72  ;cx      ; ax = sector number
   mov dx,0x00
   mov bx, 18      ; bx = number of sectors per track
   div bx         ; al = ax / bx
   mov cl, al      ; cl = real sector number (cl is used by int 13)

   ; 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
   call  write_hex32

   mov bx, 2      ; bx = number of heads
   div bx         ; ah = rest of ( ax / bx ), al = ax / bx
   call  write_hex32
   mov   ax,dx
   call  write_hex32

nogo:
        jmp   nogo