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SubjectRe: ioport conflict with "dma page reg" (0x80)
On Mon, 15 Mar 1999, Wall, Tim wrote:

> I have a single-board computer with a hardware watchdog which uses I/O
> addresses 0x80, 0x443, and 0x444.
>
> The problem is that something else in the system is writing to 0x80,
> which resets/disables the watchdog.
>

0x80 is the manufacturing test port. If you have a watchdog that
cares about that, it's broken. The kernel didn't reserve it, the
AT-Class hardware did. In fact during POST, you can read numbers
written to that port to see how far a, possibly defective, board
has gotten upon power up.

If you look in /usr/src/linux/include/asm/io.h, you will see where
it is written to anytime it is essential to slow down I/O. This works
because this port is properly handled and takes almost exactly 300 ns
for the write, regardless of CPU speed.

> I notice that the kernel reserves 0x80-0x9F for "dma page reg" (see
> /proc/ioports), but I can't find anywhere in the source that 0x80 is
> actually written to explicitly.
>
> I need to find who's stomping on 0x80 and a way to map it somewhere
> else.

You can't 'map' it somewhere else. Ports are ports decoded by PALS in
hardware (unless it's a high address going through the PCI bridge, but
that's a different thing altogether). You could change the 'outb' to
an 'inb' instruction, i.e., read the port. However, if your WD timer
is mucking with a port it definitely doesn't own, it probably won't
make much difference.


Cheers,
Dick Johnson
***** FILE SYSTEM WAS MODIFIED *****
Penguin : Linux version 2.2.3 on an i686 machine (400.59 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.


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