stop_floppy produces a 'floppy0: no floppy controllers found' message

[Frank van Dreumel]

Some time ago I bought an Asus P4T-E motherboard (a Socket 478 P4
motherboard with the Intel 850 Chipset). When I tried to boot linux by
means of syslinux or by writing a kernel directly to floppy, I got the
following message during startup:

--8<------
Floppy drive(s): fd0 is 1.44M
floppy0: no floppy controllers found
--8<------

The result being that my floppy drive was nowhere to be found. After some
extensive searching on the internet I found a solution for my problem. For
syslinux the problem could be solved by applying the following patch:

--8<------
diff -Nur syslinux-1.52/ldlinux.asm syslinux-1.52/ldlinux.asm
--- syslinux-1.52/ldlinux.asm
+++ syslinux-1.52/ldlinux.asm
@@ -2195,9 +2195,15 @@
 ; at least bootsect.S seems to imply so
 ;
 kill_motor:
+%if 1
+               xor ax,ax
+               xor dx,dx
+               int 13h
+%else
                mov dx,03F2h
                xor al,al
                call slow_out
+%endif
 ;
 ; If we're debugging, wait for a keypress so we can read any debug
messages
 ;
--8<------

For the kernel the problem could be solved by applying the following patch:

--8<------
diff -Nur linux/arch/i386/boot/bootsect.S linux/arch/i386/boot/bootsect.S
--- linux/arch/i386/boot/bootsect.S
+++ linux/arch/i386/boot/bootsect.S
@@ -395,9 +395,15 @@
 # NOTE: Doesn't save %ax or %dx; do it yourself if you need to.
 
 kill_motor:
+#if 1
+       xorw    %ax, %ax                # reset FDC
+       xorb    %dl, %dl
+       int     $0x13
+#else
        movw    $0x3f2, %dx
        xorb    %al, %al
        outb    %al, %dx
+#endif
        ret
 
 sectors:       .word 0
--8<------

And when all goes well I get the following message during startup:

--8<------
Floppy drive(s): fd0 is 1.44M
FDC 0 is a post-1991 82077
--8<------

To solve the 1024 cylinder boundary limitation of lilo, I gave grub a try
and again my floppy controller went crazy. Having seen this problem before
I tracked down the problem to the following piece of code in
grub-0.9x/stage2/asm.S:

/*
 * stop_floppy()
 *
 * Stops the floppy drive from spinning, so that other software is
 * jumped to with a known state.
 */
ENTRY(stop_floppy)
        movw    $0x3F2, %dx
        xorb    %al, %al
        outb    %al, %dx
        ret

Applying the following changes won't solve the problem (my floppy
controller still goes crazy):

 /*
  * stop_floppy()
  *
  * Stops the floppy drive from spinning, so that other software is
  * jumped to with a known state.
  */
 ENTRY(stop_floppy)
-       movw    $0x3F2, %dx
-       xorb    %al, %al
-       outb    %al, %dx
+       xorw    %ax, %ax
+       xorb    %dl, %dl
+       int     $0x13
        ret

But applying the following changes will:

 /*
  * stop_floppy()
  *
  * Stops the floppy drive from spinning, so that other software is
  * jumped to with a known state.
  */
 ENTRY(stop_floppy)
-       movw    $0x3F2, %dx
-       xorb    %al, %al
-       outb    %al, %dx
        ret

But in this case there is no point in having stop_floppy around, which
clearly can't be the correct solution. Obviously this is a rather critical
bug/feature, since it results in not being able to access my floppy disc
after booting in this way. I know it is specific to my P4T-E motherboard
because exactly the same configuration with an Asus A7V-133 or Asus A7V-266
or Asus A7V-333 motherboard instead of my P4T-E motherboard works without a
problem with both the patched and the original syslinux / kernel.

I hope I described the problem clearly enough, but if not, I'm happy to
shed more light on the problem. If you find a (possible) solution, I'll be
happy to test it on my P4T-E motherboard.

Greetz,
Frank van Dreumel
-- 
There are only 10 types of people in the world,
those who understand binary and those who don't