Re: Kernel Debugging Hardware

Geert Uytterhoeven (
Mon, 12 May 1997 12:53:34 +0200 (MET DST)

On Mon, 12 May 1997, Harald Koenig wrote:
>On May 12, Steven S. Dick wrote:
>> I believe it would be possible for <$50 to make a small device that could
>> sit on a serial port and look for kernel OOPS messages and record them
>> so that they can be examined after a reboot.
>> One possible implementation would use a serial eeprom and a pic chip
>> as a ring buffer and controller. It could be set up to just remember
>> the last several K of messages, or stop recording before overwriting
>> the first OOPS it sees, or something like that.
>good idea, I'd need it for better debuging of Xservers when the PC completely
>locks up (and of course for kernel stuff too).
>a few questions/remarks (not being too good in circuityr anymore):
>- how many write cycles are possible for eeproms these days ? I remeber of some 10k cycles ?!
> if this is still a limitation there would be no chance to log data online until
> the system will crash (ok, it would be enough to record the oops once it happend
> but that's usually not my subject)
> what about using a 8k SRAM or similar ? using e.g. Tx etc. for power supply...
> loosing data after power off is usually no big problem

Another solution that we have on Linux/m68k on Amiga: kernel messages are
logged in an otherwise unused 256K chunk of Chip RAM. In most cases the data
isn't destroyed by the crash, and you can get it back with a small AmigaOS
program that searches for some magic number at the start of the 256K chunk.

Maybe this can be extended for other architectures.



Geert Uytterhoeven           
Wavelets, Linux/m68k on Amiga
Department of Computer Science -- Katholieke Universiteit Leuven -- Belgium