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Index > OS Construction > Fails to read more than one cluster :(

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Joined: 06 Jan 2011
Posts: 200
me239 17 Jun 2011, 04:54
Hey everyone, so I just got my OS executing programs and ran into a bit of a snag. The kernel can load programs over 1 cluster fine, but fails to repeat it and just hangs. What could be wrong? Here is the code: PS sorry for the large amount of code, but it's straightforward.
xor     cx, cx
        xor     dx, dx
        mov     ax, 20h
        mul     word[RootEntries]
        div     word[BytesPerSector]
        xchg    cx, ax
        xor     ax, ax
        mov     al, byte[NumberofFATs]
        mul     word[SectorsPerFAT]
        add     ax, word[ReservedSectors]
        mov     word[datasector], ax
        add     word[datasector], cx
        mov     bx, fatbuff
        call    ReadSectors
    ;pop es
    mov cx, word[RootEntries]
    mov di, fatbuff
    push  cx
    mov   cx, 11d
    mov si, filen
    push    di
    repe cmpsb
    pop di
    jz load_fat
    pop cx
    add di, 32d
    loop    file_loop2
    jmp     progornot_notprog
        and     byte[di+0bh], 2
        jnz     progornot_notprog
        call    getfat
        mov     bx, fatbuff
        call    ReadSectors
        mov     ax, 1000h
        mov     es, ax
        xor     bx, bx
        push    bx
        mov     ax, word[cluster]
        pop     bx
        call    ClusterLBA
        xor     cx, cx
        mov     cl, byte[SectorsPerCluster]
        call    ReadSectors
        push    bx
        mov     ax, word[cluster]
        mov     cx, ax
        mov     dx, ax
        shr     dx, 1
        add     cx, dx
        mov     bx, fatbuff
        add     bx, cx
        mov     dx, word[bx]
        test    ax, 1
        jnz     odd_cluster
        and     dx, 0000111111111111b
        jmp     exdone
        shr     dx, 4
        mov     word[cluster], dx
        cmp     dx, 0ff0h
        jb      loadimage
        mov     ax, 1000h
        cmp     word[es:0], 5a4dh
        jz      RelocateEXE
       mov      ax, es
        sub     ax, 10h                 ; "org 100h" stuff Smile
        mov     es, ax
        mov     ds, ax
        mov     ss, ax
        xor     sp, sp
        push    0x0010                  ; Poins to int20 function
        push    es
        push    word 100h
        mov     ds, ax
        add     ax, [ds:08h]            ; ax = image base
        mov     cx, [ds:06h]            ; cx = reloc items
        mov     bx, [ds:18h]            ; bx = reloc table pointer
        jcxz    RelocationDone
        mov     di, [ds:bx]             ; di = item ofs
        mov     dx, [ds:bx+2]           ; dx = item seg (rel)
        add     dx, ax                  ; dx = item seg (abs)
        push    ds
        mov     ds, dx                  ; ds = dx
        add     [ds:di], ax             ; fixup
        pop     ds
        add     bx, 4                   ; point to next entry
        loop    ReloCycle
        mov     bx, ax
        add     bx, [ds:0Eh]
        mov     ss, bx                  ; ss for EXE
        mov     sp, [ds:10h]            ; sp for EXE
        add     ax, [ds:16h]            ; cs
        push    ax
        push    word [ds:14h]           ; ip
         mov     di, 5
        push    ax
        push    bx
        push    cx
        call    LBACHS
        mov     ah, 02h
        mov     al, 1
        mov     cl, byte[sector]
        mov     ch, byte[track]
        mov     dl, byte[DriveNumber]
        mov     dh, byte[head]
        int     13h
        jnc     success
        xor     ax, ax
        int     13h
        dec     di
        pop     cx
        pop     bx
        pop     ax
        jnz     @b
        mov     ax, 0e46h
        int     10h
        int     18h
        mov     al, 'S'
        mov     ah, 0eh
        int     10h
        pop     cx bx ax
        add     bx, word[BytesPerSector]
        inc     ax
        loop    ReadSectors
        mov     dx, word[di+1ah]
        mov     word[cluster], dx
        xor     ax, ax
        mov     al, [NumberofFATs]
        mul     word[SectorsPerFAT]
        mov     cx, ax
        mov     ax, word[ReservedSectors]
        sub     ax, 2
        xor     cx, cx
        mov     cl, byte[SectorsPerCluster]
        mul     cx
        add     ax, word[datasector]
        xor     dx, dx
        div     word[SectorsPerTrack]
        inc     dl
        mov     byte[sector], dl
        xor     dx, dx
        div     word[HeadsPerCylinder]
        mov     byte[head], dl
        mov     byte[track], al
sector  db      0
head    db      0
track   db      0
datasector      dw      0
cluster         dw      0
BytesPerSector  dw      512
        SectorsPerCluster db    1
        ReservedSectors   dw    1
        NumberofFATs      db    2
        RootEntries       dw    224
        SectorsPerFAT     dw    9
        SectorsPerTrack   dw    18
        HeadsPerCylinder  dw    2
        DriveNumber       db    0
Post 17 Jun 2011, 04:54
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