>This is such a simple test, though, that _anything_ could be happening within
>the processor; for example, the adder might not work at above 16 MHz, or the
>like. The test loop doesn't exercise all sides of the processor. So... any
>suggestions on how to improve on the tester, and still have a strong visual
>clue to whether it works or not?

This is interesting, since I think it indicates a fair margin of timing,
and therefore reliability, but to DESIGN a device with a clock faster than
the CPU is stamped for is INSANE.

No matter what, in 15 years, I have not had to overclock a CPU to achieve
design goals.
I took one design, 12 Mhz processor overclocked to 12.288, (and barely
getting things done) and rebuilt the software so that it worked just fine
at 3.575. I also dropped back to the 8 mhz version and saved some money :)

I overclock my PCs too, but that's my choice as the end user, with full
knowlege of the implications.
In order to qualify your devices to really be usable at the higher speed,
you'd have to run them at the min and max specified voltages, with min and
max pin loads, min and max temperatures, and excersize all on-chip
functions. This is very much non-trivial.

The idea of just using an LED as indicator is fine though, you just need to
check things internally, and then account for the fact that a processor
driven insane by your testing could possibly crash into the "blink an LED
for success" code.

It's still a useful test though, and one that I've been known to make on a
processor I don't have any experience with yet.. It lets you know where the
walls are.