[SI-LIST] OT: Overvoltage breakdown on 120 nm silicon?
- From: Dimiter Popoff <dp@xxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 17 Feb 2011 17:44:08 +0200
I am facing an unbelievable reality at the moment.
A processor which will not boot - although all tests I have
done to it pass.
I still refuse to believe I can have killed the CPU - but after
3 days of tracing of the boot process I seem to run out of
other explanations (heck, I had to dig through code some of
which I have written 15+ years ago...).
The CPU (an MPC5200B) appears to work - monitor via UART, even disk
I/O worked etc. - but it fails some way into the boot process.
This happened after I fixed the power up sequencing closer to
the specs :-).
That board had been working for nearly a year before that, had survived
the development process (lots of programming/debugging and power on/off).
It had lived through all that with a nice spike on the 1.5V, 2.5V and 3.3V
upon poweron, perhaps 1 to 5mS over the absolute maximum by perhaps
50%. I changed that now - and it won't boot, fails at more or less
the same place (pulls the wrong return address from the stack if I am
not tracing ....). This is after a few system calls have returned OK
already. It looks unbelievable to me to have killed the CPU in such
a subtle way - but I have not seen many killed ones.
How likely is it that I have killed it? The only news about the
spikes which I believe to may have killed it is that I now know they
used to exist...
Not to speak of the other boards which keep on workingfine :).
I also made the CPU check almost all of the 64M DDRAM, write address
to location/verify - works, did that with the written address rotated
0 to 31 times, also works.... And all that also misaligned,
also works fine - it is pretty maddening really.
I am simply clueless as to how likely it is to break a gate
with say 2.5V instead of 1.5? I guess drain/source breakdown won't
be an issue even if they break for a few mS (not enough energy
to fry anything)?
Hopefully people with more silicon inside knowledge can
comment...
Thanks,
Dimiter
------------------------------------------------------
Dimiter Popoff Transgalactic Instruments
http://www.tgi-sci.com
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http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/
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