Disk Read/Write Fault Using Ports in Assembly

Question

My O/S is now in protected mode so i can not access to disk using interrupts now.And I do not know how to switch to v86 mode.I need to use ports to disk access.

I decided to try the code which i found on the forum.osdev.org.In the emulator,It shows Disk Read or Write successfuly Done.But when i check the HDD it is empty or when i test reading,Buffer is all empty.

What is the problem with this code or my O/S? (Maybe Stack Problem Causes That?) CODE:

set_up_buffer:
xor ax,ax
mov es,ax
mov di,[buffer]
mov al,0xCD
stosb
mov al,0x19
       stosb
       WriteToMbr:
       mov     dx,1f6h         ;Drive and head port
       mov     al,0a0h         ;Drive 0, head 0
       out     dx,al

       mov     dx,1f2h         ;Sector count port
       mov     al,1            ;Write one sector
       out     dx,al

       mov     dx,1f3h         ;Sector number port
       mov     al,1           ;Wrote to sector one
       out     dx,al

       mov     dx,1f4h         ;Cylinder low port
       mov     al,0            ;Cylinder 0
       out     dx,al

       mov     dx,1f5h         ;Cylinder high port
       mov     al,0            ;The rest of the cylinder 0
       out     dx,al

       mov     dx,1f7h         ;Command port
       mov     al,30h          ;Write with retry.
       out     dx,al
    oogle:
       in      al,dx
       test    al,8            ;Wait for sector buffer ready.
       jz      oogle

       mov     cx,512/2        ;One sector /2
       mov     si,[buffer]
       mov     dx,1f0h         ;Data port - data comes in and out of here.
       rep     outsw           ;Send it.
       leave
       ret
buffer:
times 512 db 0

Answer 1

I FOUND THE PROBLEM,The problem was at rep outsw, so I wrote a loop code which sends words to the data register without that command. OK Here is the code I wrote in pascal:

uses ...;
var
RawData:array[0..255] of Word;
ATA_INDEX:Integer;
implementation
//...
function DiskReadSector(Drive,Head,Cylinder,SecNum:integer):Integer;stdcall;
var
xstat:Word;
i:integer;
BaseAdress:Word;
begin
if ATA_INDEX=0 then 
BaseAdress:=$1f0 else
BaseAdress:=$170;
outb(BaseAdress+6,$0a0 or (Drive shl 4) or head);
outb(BaseAdress+2,1);//Count
outb(BaseAdress+3,SecNum);// Sector Number
outb(BaseAdress+4,Cylinder and $00FF);//LOW Cylinder
outb(BaseAdress+5,Cylinder shr 8);//HIGH Cylinder
outb(BaseAdress+7,$20);//READ COMMAND $30 for WRITE
asm //CHECK FOR DATA READY
mov dx,1f7h
@still_going:
in      al,dx
test    al,8           
jz      @still_going           
end;
for i:=0 to 255 do begin //COPY DATA TO WORD ARRAY
xstat:=inw(BaseAdress); 
RawData[i]:=xstat;
end;
DiskReadSector:=inb(BaseAdress+7);//DEBUG
end

Usage:

procedure kmain;stdcall;[public,alias:'kmain'];
begin
//...
ATA_INDEX:=0;//Zero for Primary Others for Secondary 
DiskReadSector(0,0,0,1);//Drive 0 for Master 1 for Slave Example:
//ATA_INDEX=0 and Drive=0 it means Primary Master 
//This Code Will Read Master Boot Record of IDE Primary Master
//a simple check for boot signature of first sector at primary master:
if RawData[255]=$AA55 then
WriteLn('Boot Signature Detected!');
end;