AN2586 Freescale Semiconductor / Motorola, AN2586 Datasheet - Page 4

• Manufacturer Part Number: AN2586
• Description: MPC8260 PowerQUICC II Family Power Distribution Trends
• Manufacturer: Freescale Semiconductor / Motorola

Previous Work Study
Previous Work Study
To do this, we need to summarize what others have done so far.
3.1 How to estimate bypass capacitors?
Different systems consume different amounts of power even if they use the same processor. It might be
difficult to predict beforehand the amount of power a new system will consume. Many factors contribute to
this ambiguity. One of them is that it is hard to have a clear idea about the complexity of the software that
the processor are run in the early stages of the project. In [11] for example (see Section 4, “References”) a
project is made to correlate system processor measured power consumption with periodic events estimating
system usage and performance monitors. Many other similar techniques are used to produce an
energy-aware computing systems. Modern super-scaler processors like the MPC8260’s 603e core have
many units running in parallel while computing. Thus the amount of power consumed by the processor is
directly related to the sequence of code that is fed to it. Although there are simulation techniques to estimate
the power that processes consume, these simulation-estimation efforts are still tied to the sequence of
instructions that are fed to the simulator. This might be why in [11] they took direct measurement of the
power consumption rather than simulating the micro-architectural detailed power consumption. What
matters is the ability to predict the code and base on it an estimation of how much the processor is utilized.
For example. we could ask about:
One easy way might be to assume worst-case power consumption when the chip is running at its extreme
power limit as well. But this approach has its shortcomings, such as the following:
As in any engineering challenge, there has to be a reasonable compromise and an educated guess. For
example, in the MPC8260’s core current demand estimation we must know first the speed at which the core
operates. After that let us take the case when the process starts a heavy load execution. We must estimate
the number of core clock cycles needed to draw that much current and stay there steadily.
The following sets of equations are useful:
Therefore, the rate of current change can be stated as the following:
In our example, if the MPC8260 is running at 2.0 V, I is estimated 1.2 A, F = 200MH, and N = 2, then:
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How do we incorporate EMI reduction to our effort?
Data cache utilization like hit/miss ratio
Instruction cache utilization, hit/miss ratio
Register file utilization, usage
Branch prediction unit events
Integer/floating unit utilization
Too much expected current demand means undesirably stronger power supply circuit.
Too much expected current allows adding more generous copper estate, which is expensive.
Core frequency = F in Hertz.
Core single clock cycle time = 1/f in seconds.
N is the number of cycles needed to fill keep the processes working hard
I is current in Amps consumed when the processor is working hard
MPC8260 PowerQUICC II Family Power Distribution Trends: A Survey
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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MOTOROLA