PowerBug

General description of the bug:

The power-bug is a "feature" of some atx motherboards that power-off the
machine running some piece of software code. After the power-off you need to
wait some minutes before to be able to power-on again.

How I discovered the bug?

The first time my motherboard power-off was when my little brother Giacomo
was playing a new videogame. So I told my brother to not use the videgame
again. I given the due to some Windows, DirectX or videogame bug.

After some month I started to work at a project in which I had to use GCC as
a mips cross compiler. Working on the project I noticed that compiling some
times the sources the machine power-off in the same way reported by my
brother some time before. At first I given the due to overheating (also
according to Alan Cox one of the best linux kernel developer), but then I
understand that was a real bug because I was able to reproduce the power-off
simply running the cc1 (the part of GCC that translate the C preprocessed
code to machine dependent asm) two or three times only over one malicious C
file.

I tried to reverse engeneering the bug, but it' s an hard work and I have no
time to spend over an hardware bug (and to reverse engeneering the bug I had
to take my bugged motherboard and I can' t give it back to my reseller in
order to be replaced with a working one).

I am pretty sure that we can' t workaround the bug in any way. This because
the power-off happen sometimes at the second compilation, and sometimes
after some minutes of continue compilation.

How can you know if your motherboard is power bugged?

Doing some test before replace my bugged motherboard I realized that the bug
show itself only at 233Mhz (or more) and using SDIMM and not other kind of
ram that is placed on SIMM.

My processor was a Intel Pentium MMX 233Mhz but I don' t know if this can be
relevant.

To test if your motherboard is bugged I organized two test that should show
you the bug. The two tests come with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law. No warranty if some of these two tests will
damage your hardware or your software. Run it only at your own risk.

   * If you use linux you only need to download this file, extract it and
     then run `make`.
   * If you are not using linux you must install linux and goes to the point
     before or install DOS and run the `poweroff.bat` script that you will
     find in this other file. This DOS version of the test will boot linux
     so after running `poweroff.bat` you will need to reboot in order to
     return in DOS.

Which hardware is known to be bugged?

Sure my ActiveI Admiral motherboard. The newer Admiral Value (also from
ActiveI) is sure bugged too since at first my reseller has replaced my
motherboard with it but with no success.

I have some report from other people that has a power bugged motherboard but
currently I have not details about their hardware.

                                                           Andrea Arcangeli

$Id: powerbug.html,v 1.4 1998/02/15 15:26:21 andrea Exp $