So basically your problem is that you can't code assembly. It's pretty stupid then abandoning C.abuashraf wrote:I already wrote complete fat12 driver in C,but now I'm writing it in asm
but I'm really having problem with this specific function
I really fail to understand that, if you have a working C-version, you are not able to make an assembly one. What is your problem?abuashraf wrote:I wrote a lot of Dos programs,but I'm having trouble with this specific fumction
. You might find this more readable than the official Microsoft specs Code: Select all
setcluster:
push cx dx bx
mov cx, ax ;copy current cluster
mov dx, ax ;copy current cluster
shr dx, 0x0001 ;divide by two
add cx, dx ;cx=offset into FAT
mov bx,[es:0x500] ;address of fat table
add bx, cx ;index into FAT
mov dx, WORD [bx] ;read two bytes from FAT(old value in dx)
test ax, 0x0001
jnz .odd
.eve:
mov bx,dx
and bx,0xF000 ;bx holds the old value
and word[value],0x0FFF ;next cluster
or word[value],bx
mov dx,word[value]
mov word [bx],dx
jmp donexx
.odd:
mov bx,dx
and bx,0x000F ;bx holds the old value
shl word[value],4 ;next_cluster
or word[value],bx
mov dx,word[value]
mov word [bx],dx ;save the new value
donexx:
pop bx dx cx
ret
Code: Select all
setcluster:
push cx
mov cx, ax ;copy current cluster
mov dx, ax ;copy current cluster
shr dx, 0x0001 ;divide by two
add cx, dx ;cx=offset into FAT
mov bx,[es:0x500] ;address of fat table
add bx, cx ;index into FAT
push bx
mov dx, WORD [bx] ;read two bytes from FAT(old value in dx)
test ax, 0x0001
jnz .odd
.eve:
mov bx,dx
and bx,0xF000 ;bx holds the old value
and word[value],0x0FFF ;next cluster
or word[value],bx
mov dx,word[value]
pop bx
mov word [bx],dx
jmp donexx
.odd:
mov bx,dx
and bx,0x000F ;bx holds the old value
shl word[value],4 ;next_cluster
or word[value],bx
mov dx,word[value]
pop bx
mov word [bx],dx ;save the new value
donexx:
pop cx
ret