FAT32 opening files

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superos

Joined: 24 Apr 2013
Posts: 10

superos

Hello,
I have a problem with support for FAT32, and more do not know how to do it.
Does anyone know where there is a specification for FAT32, or implementation code in asm?

24 Apr 2013, 10:12

cod3b453

Joined: 25 Aug 2004
Posts: 619

cod3b453

You can find the specification here http://msdn.microsoft.com/en-gb/library/windows/hardware/gg463080.aspx

24 Apr 2013, 16:43

superos

Joined: 24 Apr 2013
Posts: 10

superos

Thank you.
Besides, I have a little problem with the code for displaying text.

Code:

pisz_tekst:
        pusha
 .powtorz:

        lodsb
        mov bh, 0
        cmp al, 0
        je .gotowe

        call pisz_litere
        ; je[li znak to zero to zakoDcz
       mov ah, 0Eh
       int 10h                         ; w przeciwnym razie go drukuj
        jmp .powtorz                     ; i przenie[ si do nazstpnego znaku

 .gotowe:
        popa
        ret

pisz_litere:
        pusha
        mov ah, 0Eh
        int 10h
        popa
        ret

Unfortunately, the text is not displayed. At the beginning of the cursor around the screen goes crazy, and after three seconds it. Unfortunately, previous letters disappear (entered manually).
I refer to a function like this:

Code:

 mov si, komunikat1
 call pisz_tekst 
........
komunikat1 db "Test",0

Has anyone already had this problem?

25 Apr 2013, 14:34

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr

superos,

Well, there are some problems. You're using int10/0E service twice for the same character (first inside pisz_litere(), second right after call). With this error corrected, your code runs fine (you must ensure proper ds for lodsb).

25 Apr 2013, 16:47

superos

Joined: 24 Apr 2013
Posts: 10

superos

Thanks for the reply. I did not notice that repeats Smile

. I tried to improve the code, as you said, and now the garbage is not displayed, but unfortunately it will not display the text. Here is my code:

Code:

pisz_tekst:
        pusha
        mov ds, si
 .powtorz:

        lodsb
        mov bh, 0
        cmp al, 0
        je .gotowe
        ; je[li znak to zero to zakoDcz
       mov ah, 0Eh
       int 10h                         ; w przeciwnym razie go drukuj
        jmp .powtorz                     ; i przenie[ si do nastpnego znaku

 .gotowe:
        popa
        ret

What must I do to be displayed a text?

2.I have another question. Do anyone know how to capture clicking the "windows" on the keyboard? I tried with:

Code:

czekaj_na_nacisniecie_klawisza:
        mov ax,0
        mov ah,10h
        int 16h
        ret

but I managed to capture key "windows" or "menu", but others like "a, b, c ..." Do anyone know how to read these nonstandard keys?

25 Apr 2013, 17:24

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr

superos,

You set up ds incorrectly (most probably so). Show your entire code (I think you are using format MZ, aren't you?).

As to your second question, have you tried int16/10 from plain DOS (not NTVDM or any other emulator)? Under Windows WinKey and AppKey are handled differently than regular keys.

I quickly brewed simple example with two segments:

Code:

        format  MZ

        segment @CODE
        entry   @CODE:start
start:  mov     ax, @DATA
        mov     ds, ax          ; ds contains @DATA selector
        mov     ah, 0Fh
        int     10h             ; get active page in bh
        mov     si, banner      ; now ds:si = @DATA:banner
        call    printsz
.next:  mov     ah, 10h
        int     16h
        cmp     ax, 011Bh       ; Esc?
        je      .done           ; yes, finish
        mov     dx, ax          ; no, pass BIOS scan code
        call    printwx         ; to print function
        mov     ax, 0E00h + ' ' ; print ' ' to separate numbers
        int     10h             ; using int10/0E (ax = 0E20h)
        jmp     .next
.done:  mov     si, crlf
        call    printsz
        mov     ax, 4C00h
        int     21h

;;; Print (int10/0E) ASCIIZ
;;; Expects: ds:si = far pointer to ASCIIZ
;;;          bh = video page for output
printsz:
        push    ax
        mov     ah, 0Eh
.next:  lods    byte [ds:si]
        test    al, al
        jz      .done
        int     10h
        jmp     .next
.done:  pop     ax
        ret

;;; Print hex word
;;; Expects: dx = word to print
;;;          bh = video page for output
printwx:
        call    @f
@@:     xchg    dh, dl
;;; fall through

;;; Print hex byte
;;; Expects: dl = byte to print
;;;          bh = video page for output
printbx:
        call    @f
@@:     ror     dl, 4
;;; fall through

;;; Print hex nibble
;;; Expects: dl[3:0] = nibble to print
;;;          bh = video page for output
printnx:
        push    ax
        mov     ax, 0E0Fh
        and     al, dl
        cmp     al, 10
        sbb     al, 69h
        das
        int     10h
        pop     ax
        ret

        segment @DATA
banner  db      "Press keys to see their BIOS int16/10 codes (Esc to quit)"
crlf    db      13, 10, 0

25 Apr 2013, 19:41

superos

Joined: 24 Apr 2013
Posts: 10

superos

My code:

Code:

mov si, komunikat1
mov ax, 0
mov ds, ax
call pisz_tekst

Ok, thanks for your help baldr. Your code did not want too much work, but he told me a lot. As I write its own operating system, I can use DOS, so I would have keyboard support in bios. Do you know how to use can interrupt the BIOS check if you press the Windows key?

26 Apr 2013, 15:00

superos

Joined: 24 Apr 2013
Posts: 10

superos

Welcome. I have a problem with the service diskette. I tried this code:

Code:

 
bufor_dysku db 512 dup(1),0  
odczytaj_liste_plikow:
mov dh,0
        mov dl, [bootdev]
        mov cx,19

        mov ah, 2             ;funkcja odczytaj sektory
        mov al, 1             ;liczba sektorow  do przeczytania
        mov si,bufor_dysku
        mov es,si
        mov bx,0   ;offset bufora

        int 0x13 
        ret
bootdev db 0

unfortunately it does not work. Does anyone know how to solve this problem? Would have been nice, as if someone had a library to support FAT32 - it would be much easier for me. Regards.

27 Apr 2013, 13:33

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr

superos,

Be careful. You repeat the very same error again: es should contain selector, and you load it with offset of bufor_dysku (this should go to bx).

If BIOS service fails, it returns status code (if you supply it, that may help). Does your boot device really have sector 0/0/19?

29 Apr 2013, 06:55

DOS386

Joined: 08 Dec 2006
Posts: 1901

DOS386

> Does anyone know where there is a specification for FAT32

Spec of BAD filesystem FAT28: http://www.jafile.com/uploads/dos386/fat28ms.pdf (100 KiB PDF)

> have been nice, as if someone had a library to support FAT32 - it
> would be much easier for me.

http://www.fullfat-fs.co.uk/

29 Apr 2013, 07:09

BAiC

Joined: 22 Mar 2011
Posts: 272
Location: California

BAiC

you need to divide the address of the buffer by 16 before storing in a segment register (assuming 16bit code). if it's not aligned on a 16byte boundary then you need to also store (address and 15) into bx.

Code:

bufor_dysku db 512 dup(1),0  
odczytaj_liste_plikow:
mov dh,0
        mov dl, [bootdev]
        mov cx,19

        mov ah, 2             ;funkcja odczytaj sektory
        mov al, 1             ;liczba sektorow  do przeczytania
        mov si,bufor_dysku/16
        mov es,si
        mov bx,bufor_dysku and 15;offset bufora

        int 0x13 
        ret

_________________
byte me.

29 Apr 2013, 16:07

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr

BAiC,

Your suggestion will be valid iff bufor_dysku is an offset in segment 0; for any other segment selector you need to take in account that selector too. And why bother to convert perfectly valid 0:bufor_dysku far pointer into (also perfectly valid) bufor_dysku shr 4:bufor_dysku and 15 huge pointer?

29 Apr 2013, 17:47

BAiC

Joined: 22 Mar 2011
Posts: 272
Location: California

BAiC

baldr: read my fucking post: I explicitly declared that it assumes 16bit code. a segment selector is protected mode (32bit code).

_________________
byte me.

29 Apr 2013, 19:12

superos

Joined: 24 Apr 2013
Posts: 10

superos

baldr
I have corrected my mistake. It turned out that the track is 18 sectors. nay even in the 18 - 36 sectors varies head ...

Code:

mov ah, 2             ;funkcja odczytaj sektory
        mov al, 1             ;liczba sektorow  do przeczytania
        mov ch, 0             ;numer [cie|ki
        mov cl, 2            ;numer sektora niby |e 19
        mov dh,1             ;numer gBowicy

It works perfectly.
But now I have a problem with searching for files on the disk. Here is my code:

Code:

;funkcja ladowania plików pod dany adres
;bx - sciezka
;si - docelowe miejsce
laduj_sciezke:
        pusha
        push bx
         mov bx,bufor_dysku   ;offset bufora
        mov ah, 2             ;funkcja odczytaj sektory
        mov al, 1             ;liczba sektorow  do przeczytania
        mov ch, 0             ;numer [cie|ki
        mov cl, 2            ;numer sektora niby |e 19
        mov dh,1             ;numer gBowicy
        mov dl, [bootdev]
        mov si,0
        mov es,si
        int 0x13
        call restartuj_naped
        pop bx
        ;sprawdzanie nazwy pliku
        mov cx,16
        pnazw:
        mov si,0
        mov ds,si
        mov si,bufor_dysku
        pusha
        mov dl,0
        petla1:
        lodsb
        mov di,0
        mov es,di
        mov di,bx
        mov ah,byte[es:di]
        cmp al,ah
        jne dalejbonie
        add si, 20
        inc dl
        cmp dl,11
        jne petla1
        ;<==== Code if it's the file you need.
        dalejbonie:
        mov dh,11
        sub dh,dl
        mov dh,0
        add si, dx
        mov [adresst],si
        popa
        mov si, [adresst]
        loop pnazw

        popa
        ret
        adresst dw 0

I do not know what is wrong. Even my eyes hurt from looking for that "something" ...

I corrected the post. I'm sorry for the mistakes, but I translated by Google Translate. I'm sorry again.
I mistook the nickname. Razz

Last edited by superos on 01 May 2013, 15:57; edited 1 time in total

01 May 2013, 12:39

BAiC

Joined: 22 Mar 2011
Posts: 272
Location: California

BAiC

Quote:

I have corrected your mistake.

my mistake?

_________________
byte me.

01 May 2013, 13:48

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr

BAiC wrote:

baldr: read my fucking post: I explicitly declared that it assumes 16bit code. a segment selector is protected mode (32bit code).

I read it well. Consider this:

Intel® 64 and IA-32 Architectures Software Developer’s Manual, rev. 046US, Vol. 1 wrote:

3.4 BASIC PROGRAM EXECUTION REGISTERS
…
3.4.2 Segment Registers
The segment registers (CS, DS, SS, ES, FS, and GS) hold 16-bit segment selectors. A segment selector is a special pointer that identifies a segment in memory. To access a particular segment in memory, the segment selector for that segment must be present in the appropriate segment register.

Intel® 64 and IA-32 Architectures Software Developer’s Manual, rev. 046US, Vol. 3 wrote:

20.1 REAL-ADDRESS MODE
…
20.1.1 Address Translation in Real-Address Mode
In real-address mode, the processor does not interpret segment selectors as indexes into a descriptor table; instead, it uses them directly to form linear addresses as the 8086 processor does. It shifts the segment selector left by 4 bits to form a 20-bit base address (see Figure 20-1). The offset into a segment is added to the base address to create a linear address that maps directly to the physical address space.

Perhaps you should contact Intel to tell them the truth. Wink

----8<----
superos,

mov ah, byte [es:di] always retrieves first character of file name you're searching for (since neither bx nor di are advanced). If the character matches that of first directory entry, you increase pointer by 20 (now it'll point to reserved byte right before modification time) and continue comparison (with that first character !?). If character doesn't match, you do some calc with dh, then zero it (!) and add resulting dx to si (as a result, comparison will restart).

How does this supposed to work?

01 May 2013, 15:19

BAiC

Joined: 22 Mar 2011
Posts: 272
Location: California

BAiC

Quote:

Perhaps you should contact Intel to tell them the truth.

Intel has a history of writing the current version of their documentation from the perspective of the current model. When protected mode was developed the term "selector" was used to refer to the selection of a segment within the Global/Local Descriptor Table. as such; in normal conversation between people who know anything about the Intel Architecture a segment selector is a reference to atleast the Protected Mode model.

_________________
byte me.

01 May 2013, 15:46

superos

Joined: 24 Apr 2013
Posts: 10

superos

All code files in a directory search is to work like this: the bx I give the path to the file (for now just the name of the file in the root directory) and ds: si gives the address to which to read the file.
Sorry if Google Translate again, again I feel bad translate.

I also have a problem with service interruption 0 - divide by zero. Well, breaking up is doing, but the mode when the end make a new start to perform over and over again. Here is my code:

Code:

;setting interrupt
cli
mov ax,0                               ;zerowanie
mov es,ax                              ;zerowanie
mov [es:0],word dzielenie_przez_zero   ;offset
mov [es:2],word 0                      ;segment
sti

;main function of interrupt
dzielenie_przez_zero:
cli

        push ds
        push es
        pusha
        mov bl, 1fh
        mov dl,0
        mov dh,0
        mov si, 80
        mov di,25
       call rysuj_kwadrat
       mov dh,12
       mov dl,37
       call przesun_kursor
       mov ax,0
       mov ds,ax
        mov si,komunikat5   ;tekst "wystapiB bBd dzielenia przez zero"
        call pisz_tekst

        call odswiez_GUI
        popa
        pop es
        pop ds

        sti
        iret

01 May 2013, 16:07

BAiC

Joined: 22 Mar 2011
Posts: 272
Location: California

BAiC

superos: post all of your code, not simply a section of the code.

_________________
byte me.

01 May 2013, 16:29

superos

Joined: 24 Apr 2013
Posts: 10

superos

Well, just about the last problem - the code it works fine, but it's performed in a circle. If I call it the "call" works fine, but if by "mov al, 0 div al" is invoked over and over again. I will not give the whole code, because it is contained in seven files, and each of them is long.

01 May 2013, 16:44

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