OSDev.org

Posted: **Wed Dec 24, 2008 1:08 am**

I have basically finished my Floppy driver. Everything works fine except the data it is reading is not what is really on the disk. When I read the 1st sector (Boot Sector) The first byte should be EB however I am getting a different value. I have checked my code against various sources but all seems to be fine. My transfer code is

Code: Select all

function FloppyDoTrackLBA(Drive : byte; LBA : byte; dir : byte; NoSectors : byte) : byte;
var
cmd, i, st0, st1, st2, rcy, rhe, rse, bps, error : byte;
cyl, head, sec : byte;
begin
error := 0;

case dir of
1  : cmd := FloppyCmd[5] ;//or $C0; //Read
2  : cmd := FloppyCmd[4] ;//or $C0; //Write
end;

LBA2CHS(LBA, cyl, head, sec);
Size := NoSectors * 512;

if (Seek(Drive, cyl, head)) = -1 then
  begin
  FloppyDoTrackLBA := -1;
  Exit;
  end;

for i := 1 to 20 do
 begin
   Motor(Drive, 1);
   FloppyDMAInit(dir, Size);

   Delay(10);

   FloppyWriteCmd(Drive, cmd);
   FloppyWriteCmd(Drive, ((head shl 2) or Drive));
   FloppyWriteCmd(Drive, cyl);
   FloppyWriteCmd(Drive, head);
   FloppyWriteCmd(Drive, sec);
   FloppyWriteCmd(Drive, 2);
   FloppyWriteCmd(Drive, 0);
   FloppyWriteCmd(Drive, 0);
   FloppyWriteCmd(Drive, $FF);

   IRQWait(6);

   st0 := FloppyReadCmd(Drive);
   st1 := FloppyReadCmd(Drive);
   st2 := FloppyReadCmd(Drive);

   //Read Cylinder, Head, Sector
   rcy := FloppyReadCmd(Drive);
   rhe := FloppyReadCmd(Drive);
   rse := FloppyReadCmd(Drive);

   bps := FloppyReadCmd(Drive);

   if error = 0  then
    begin
      Motor(Drive, 0);
      FloppyDoTrackLBA := 0;
      Exit;
    end;

   if error >= 1 then
    begin
      PrintString(#10'Floppy Read Write Fail.. Quiiting');
      Motor(Drive, 0);
      FloppyDoTrackLBA := -2;
      Exit;
    end;
 end;
 
PrintString(#10'Floppy Read Write Timeout');
Motor(Drive, 0);
FloppyDoTrackLBA := -1;
end;

The other problem I am experiencing is that the Driver won't write to a floppy. In Bochs I get a "Cannot write() to floppy image" exception but on real hardware nothing gets written. My read and write codes are as follow:

Code: Select all

function FloppyRead(Drive : byte; Data : byte; LBA : boolean; NoSec : byte) : byte;
begin
if LBA = false then
  FloppyRead := FloppyDoTrack(Drive, Data, 1);

if LBA = true then
  FloppyRead := FloppyDoTrackLBA(Drive, Data, 1, NoSec);
end;

                    //Drive to be used, Starting Sector, Uses LBA (T/F), Number of sectors to read
function FloppyWrite(Drive : byte; Data : byte; LBA : boolean; NoSec : byte) : byte;
begin
if LBA = false then
  FloppyWrite := FloppyDoTrack(Drive, Data, 2);

if LBA = true then
  FloppyWrite := FloppyDoTrackLBA(Drive, Data, 2, NoSec);
end;

Ignore those IF Then statements. I have to different read algorithms. But I am only using "FloppyDoTrackLBA" at the moment. The other one is an experimental thing.
Is there something I am missing that makes it possible to write to a floppy? I will post more code if you need.

OSDev.org

FDD Read not reading correct sectors

FDD Read not reading correct sectors