That is very close for CMOS logic, such as comprises most of modern microprocessors.
Not enough so to worry about.
-- --Larry Brasfield email: donotspam_larry_brasfield@hotmail.com Above views may belong only to me.
Except that at 1 GHz, the processor would be able to run at a lower core voltage. The power dissipation is proportional to the core voltage squared.
Paul
If an AMD processor with no special power-saving features is drawing 200 Watts while running at 2 GHz with a 200Mhz Front side buss, How many watts will it draw while running at 1 GHz with a 100Mhz FFB? 100W? Is that the formula, half the frequency means half the heat generated? Or is it more complicated than that?
Watts
The OP strongly implied that unmentioned variables were unchanged. His question makes little sense otherwise. If we must mention all those variables, we should include loading on the uP pins, nature of the code being run, its time dependencies, etc.
-- --Larry Brasfield email: donotspam_larry_brasfield@hotmail.com Above views may belong only to me.
200 Watts
will it
formula,
Do they do that?
I know that some microprocessor power supply contollers are supplied with D/A converters to adjust the output voltage.
Sort of makes sense that they might be able to do it dynamically according to the sums being done.
Clever stuff.
DNA
Watts
The processes that modern microprocessors use leak like hell (both gate oxide tunneling and sub-threshold) and it's getting worse. Much of the power dissipation is DC and is unaffected by the clock frequency. Only the dynamic power component is proportional to frequency.
Complete bullshit.
-- Keith
Sure. For the range of processors being talked about here, whenever power consumption of CPUs is seriously considered (e.g. because it's a mobile computer running off a battery whose weight you have to justify), core voltage modulation is a routine operation in modern designs --- the capability of doing this dynamically is the only real difference between e.g. Mobile and Desktop versions of the same x86 processor family. For the AMD processors mentioned by the OP, google up "PowerNow!".
-- Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de) Even if all the snow were burnt, ashes would remain.
Dynamic average power = Ctotal*Vdd^2*fclk
so assuming all 200W is dynamic power(which it is not) Ctotal is constant Vdd^2 is constant
Pavg is proportunal to fclk.
One other thing that is relevant mainly in real-time control systems.
In such systems, it is quite common to perform a more os less constant amount of work (say 500000 instructions or cycles) at very regular intervals (say every millisecond) and the rest of the interval, the processor is idle. In this example, those 500000 cycles would take
0.25 ms in every interval to execute at 2 GHz.Dropping the clock frequency to 1 GHz, it would now take 0.5 ms to execute the program in each 1 ms interval. Although the instantaneous power dissipation drops to 1/2, the execution time doubles, so the total energy dissipated remains constant during each interval and hence the average power dissipation remains constant.
The only gains that you can get some power saving in such applications is from such circuits that are running constantly regardless if the CPU is doing any real work or not or by lowering the core voltage.
Other systems that needs to do a constant amount of work (instructions) in a specified time (such as various media players) may behave in a similar manner.
Paul
Watts
Given that as a fact, one has to wonder why so much trouble is taken with clock speed reduction in mobile processors.
True by definition and not at issue.
Since you are so all-knowing, how about listing the DC current versus dynamic current for a few AMD processors to give the OP an idea of what kind of error he can expect to incur by using the Idc == 0 approximation? (In other words: "Evidence please.")
-- --Larry Brasfield email: donotspam_larry_brasfield@hotmail.com Above views may belong only to me.
Watts
it
Reduce the clock speed and you can also reduce the voltage. Reduce the voltage and the leakage decreases too (by at least the third power). It's not hard to see why one reduces the clock speed in mobile applications.
No, not by definition. The dynamic power is also a second order function of the voltage, is that the definition of "dynamic power"? It *is* the issue, since the question was asked about (total) power, not a component of the power.
At 90nm and fast-sort processors, it's upwards of a 50% error (assuming no Vcore modulation). Is that enough of an error to admit you haven't been paying attention for a few years?
-- Keith
Yes, that's a very relevant observation. It's actually worse since doubling the clock doesn't get twice as much work done (still the same wait for memory, for instance). Also the Vcore can be throttled down at a lower clock frequency, saving both dynamic and static power. If the actual needs are known ahead of time, a processor intended for a slower clock can save even more because it can be designed/processed/sorted (in any combination) for low power rather than high clock rates.
Sure, but if you lower both the voltage and the clock rate you may be able to save even more.
Sure. In this case a processor chosen specifically for the application is the best bet.
-- Keith
BTW, nice picture! ;-)
Watts
will it
Interesting.
Dynamic power is the power dissipated due to charging capacitances. There was no voltage change in the OP's question. Maybe that should be assumed on his behalf.
The question was how power varies when the clock speed is changed.
Yes. The last time I looked into this, the short channel and gate tunnelling effects were still on the horizon as a predicted limit to Moore's law.
It looks like the OP needs to look at a spec for the actual AMD part he has in mind.
-- --Larry Brasfield email: donotspam_larry_brasfield@hotmail.com Above views may belong only to me.
200 Watts
will it
formula,
Will you never have a high enough IQ to be able to rent a clue? What, pray tell, do you think the buzz has been about for the last couple of years? Moore's law has come to a *big* speed-bump, and that's *LEAKAGE*. Sheesh!
IFF they want you to know the answer. If you're good (you're not) you might be able to ferret out some information. However, they're (AMD and Intel) cozy with the facts.
-- Keith
This is not a Trivial Pursuit game with a single correct answer or a homework help desk for lazy students, this is a news group that traditionally has been used for open ended discussions, in which participants can learn from by actively taking part in the discussion or by just following the discussion.
As in engineering in general, there are usually not a single "correct" answer, but it usually depends on many factors, which were not obvious or stated in the original posting that stated a thread.
If this was a homework, I hope that the original poster has been followed the whole thread and learned much more than from just a Yes/No answer. Paul
The following '|>>|' quoted text is restored context necessary to understand Paul's bare quotation.
|>>|>> > Only the dynamic power component is proportional to frequency. |>>|>>
|>>|>> True by definition and not at issue. |>>|>
|>>|> No, not by definition. The dynamic power is also a second order |>>|> function of the voltage, is that the definition of "dynamic power"? |>>| |>>|Dynamic power is the power dissipated due to |>>|charging capacitances. There was no voltage |>>|change in the OP's question. Maybe that should |>>|be assumed on his behalf. |>>| |>>|> It *is* the issue, since the question was asked about (total) power, |>>|> not a component of the power. |>>|
I agree with what you are saying but object to your use of a quote lifted out of its context to imply that I need such a tutorial. Without the context, you make it appear that I attempted to constrain the discussion. The (now restored) context shows otherwise.
That lesson, too, is worthy but already well taken. ...
-- --Larry Brasfield email: donotspam_larry_brasfield@hotmail.com Above views may belong only to me.
Once again, you don't know what the hell you're talking about...try going to hell and staying there.
An interesting read on power consumption and leakage is this:
Joop
On Sat, 23 Apr 2005 03:27:10 +0000, Fred Bloggs wrote: ...
Oh, crap. I've just discovered that my plonkfile expires.
Bloggs, have you _ever_ posted _anything_ having anything to do with electronics, or do you fill up your days merely spewing venom?
Thanks, Rich
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