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

How could anyone tell you what is wrong with your OS. You haven't shown us anything about it. — Sep Roland, Jun 26 '16 at 20:09
@SepRoland Experienced O/S Developer can guess something about it — user2590769, Jun 26 '16 at 20:17
You think! For starters, why do you assume that every HD in this world uses *these* ports? — Sep Roland, Jun 26 '16 at 20:21
I know IDE Primary Master Uses 1fxh.And I am trying on IDE primary Master.I can detect IDE using PCI. @SepRoland — user2590769, Jun 26 '16 at 20:34
Also emulator says Disk Write or Read Done.But Nothing Happens Both. — user2590769, Jun 26 '16 at 20:34
If you are in 32 bit protected mode, loading 16 bit addresses is very suspicious. Also, post [MCVE], we can't debug this. — Jester, Jun 26 '16 at 21:24
@Jester If i exchange 16 bit registers with 32 bit registers,Will it solve? — user2590769, Jun 26 '16 at 21:50
How should I know? That's just suspicious by itself, because you might not be using the correct address at all. So you are looking at the wrong memory. You should really learn to debug before you start messing with OS stuff. — Jester, Jun 26 '16 at 21:52
@Jester I wrote full code now and I have knowledge about debugging.Check it out if i am missing something then answer the full working code please — user2590769, Jun 26 '16 at 21:58
Are you **really** in protected mode? Zeroing `es` can't be good. This code should fault immediately at `stosb`. — Jester, Jun 26 '16 at 22:02
Yes it halts in es so i remove it when it is in protected mode @jester — user2590769, Jun 26 '16 at 22:04
You need to make sure you load `es:edi` properly. Until then, you can't even start dealing with the actual i/o stuff. Use the debugger to examine values. — Jester, Jun 26 '16 at 22:05
i have diffrent code for protected mode which makes buffer's first two bytes CD 19 — user2590769, Jun 26 '16 at 22:06
The problem not in there i debug it buffers first to byte is correct but HDD is always filled with zeroes — user2590769, Jun 26 '16 at 22:07
Status register marked dsc and drq at the same time when writing. — user2590769, Jun 26 '16 at 22:11
@Jester if you have code about Disk R/W using assembly with ports then just post an answer to this question — user2590769, Jun 26 '16 at 22:13
See [osdev.org](http://wiki.osdev.org/ATA_PIO_Mode#ATA_Driver) — Jester, Jun 26 '16 at 22:15
@Jester you must me kidding me.I copied this code from there. — user2590769, Jun 26 '16 at 22:16
Somewhere else, not the code I linked. It doesn't look similar. — Jester, Jun 26 '16 at 22:19
I will check it out later and if you are interested in that, i will make you know about results @Jester — user2590769, Jun 26 '16 at 22:25

score 1 · Answer 1 · edited Jun 27 '16 at 12:14

1

mov si, [buffer] seems wrong, since it moves the contents of the buffer, instead of the buffer's address.

It should be mov si, buffer or lea si, [buffer], I would think.

edited Jun 27 '16 at 12:14

Cody Gray - on strike

239,200
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490
574

answered Jun 26 '16 at 22:31

Frank Kotler

3,079
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user2590769 · Accepted Answer · 2016-06-27T12:47:37.513

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;

You should post the updated code *here [in your answer](http://stackoverflow.com/posts/38050286/edit)*. — Cody Gray - on strike, Jun 27 '16 at 12:13

Disk Read/Write Fault Using Ports in Assembly

2 Answers2