Great points, thanks Cliff.
Jeremy
--- In A..., "techguy2000" wrote:
>
> --- In A..., "jeremywang2008" wrote:
> >
> > Thank you all, guys.
> >
> > Now I believe I can't do it, but I'm wondering why 7XC256 can
be
> > overclocked to that high and just working well.
> >
> > To Kris:
> > I also tried your solution, set PLL out to 192MHz, then divide by 2,
> > but it fails too.
>
> You: 1) probably just had a good chip and 2) probably weren't
> hitting any temperature extremes.
>
> Processors that are speed graded often use the same core and the
> different speed grades are determined by actually testing the
> processor at temperature extremes. It's usually the high temperature
> end that has a problem with higher clock rates. Overclockers have to
> go to extremes in cooling solutions because they need to keep the part
> cooler than the max rated temperature for it to operate at the higher
> speeds plus the parts will draw more power at the higher speeds.
>
> The Atmel SAM7 parts are not speed graded and the maximum speed is
> determined by a characterization of the parts and the max frequency
> that will give a good yield. So the 55MHz rating is the frequency
> that 99.9% (or whatever their target yield is) of the processors will
> run at over the full temperature range. Some parts will be able to
> run faster. All parts should be able to run faster over a more
> restrictive temperature range. How fast depends on the individual
> parts. As the manufacturing process is refined for a particular
> component, you will usually get a higher percentage of parts that can
> run faster than the rated speeds.
>
> The two devices probably don't have the EXACT same core.
They're
> probably very similar, but the different memory sizes are likely to
> cause some differences that could affect performance.
>
> Exceeding any parameters in an electronic design is like playing
> Russian Roulette. It may work on a case by case basis, but you'll
> eventually get bitten if you do it often enough.
>
> Cliff
>
Help: AT91SAM7XC512 can't work on 96 MHz
Started by ●January 21, 2009
Reply by ●January 22, 20092009-01-22
Reply by ●January 25, 20092009-01-25
Rick Collins wrote:
> There are two possibilities. One is that your chip is just a really
> fast chip. It happens. There is always variation in the
> manufacturing process. The specs have to allow for the worst case in
> several ways, process, voltage and temperature.
>
> The other possibility is that the chip really isn't running at 96 MHz.
> Maybe there is a mistake in the setup and it is running at some other
> speed.
There is a third possibility. Maybe only a subset works and the test
cases he used only used that subset. I accidentally overclocked a chip
once and the only observable fault was the baud rate wouldn't set
correctly (it was lower than expected).
Robert
> There are two possibilities. One is that your chip is just a really
> fast chip. It happens. There is always variation in the
> manufacturing process. The specs have to allow for the worst case in
> several ways, process, voltage and temperature.
>
> The other possibility is that the chip really isn't running at 96 MHz.
> Maybe there is a mistake in the setup and it is running at some other
> speed.
There is a third possibility. Maybe only a subset works and the test
cases he used only used that subset. I accidentally overclocked a chip
once and the only observable fault was the baud rate wouldn't set
correctly (it was lower than expected).
Robert
