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orthogonal experimental data?

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  • 08-09-2010 2:02pm
    #1
    x in the city
    Closed Accounts Posts: 7,134 ✭✭✭


    Guys,

    Has anyone experience of the above, I was told its possible to calculate an optimum power figure across a range of frequencies, voltages, and power averages etc.

    But its all up in the sky for me, any shed light on this?!


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    #2
    bnt
    Registered Users Posts: 12,961 ✭✭✭✭bnt


    When I hear "power" and "frequency", the first thing this brings to mind is the concept of Power Factor in AC circuits. A power factor of 1 means that voltage and current are in phase, which means optimum power transfer. When they're out of phase by a phase angle q, the Power Factor is Cos q, and power transfer is less than optimum. This happens because of a net reactance (inductive or capacitive), but if you can work it out, you can do power factor correction by adding components. Are you working on an AC circuit of some kind?

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    #3
    x in the city
    Closed Accounts Posts: 7,134 ✭✭✭x in the city


    bnt wrote: »
    When I hear "power" and "frequency", the first thing this brings to mind is the concept of Power Factor in AC circuits. A power factor of 1 means that voltage and current are in phase, which means optimum power transfer. When they're out of phase by a phase angle q, the Power Factor is Cos q, and power transfer is less than optimum. This happens because of a net reactance (inductive or capacitive), but if you can work it out, you can do power factor correction by adding components. Are you working on an AC circuit of some kind?

    nope, more like the attachment...!


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    #4
    Turbulent Bill
    Registered Users Posts: 1,622 ✭✭✭Turbulent Bill


    No experience, but looking at the graph you can total the power consumption for each operating frequency across the different (supply?) voltages - clearly the highest frequency means the highest power. Work out the number of cycles required for the operation, find the total energy required for each operating frequency to find which is most efficient?

    In practice you're probably limited to whatever operating frequency the circuit uses.


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    #5
    king_of_inismac
    Registered Users Posts: 1,365 ✭✭✭king_of_inismac


    clearly the highest frequency means the highest power.

    Wouldn't be so sure about that one mate! :)


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    #6
    Turbulent Bill
    Registered Users Posts: 1,622 ✭✭✭Turbulent Bill


    king_of_inismac wrote: »
    Wouldn't be so sure about that one mate! :)

    That's exactly what the graph suggests - the highest power across almost all voltage levels is at the highest frequency level. I've no idea what the component actually does, whether the voltages/powers are input or output etc., only that there's a positive correlation with power and frequency.


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    #7
    x in the city
    Closed Accounts Posts: 7,134 ✭✭✭x in the city


    Bill is right, hiver voltages and higher freq will use more power of course and complete tasks in a quicker time frame as opposed to lower voltages and slower clocks.

    I am wondering how I can go about getting an optimum value for a particular code function... Im not sure i understand how to go about this.

    I can calculate the energy in jules for different voltages/frequencies but this wont be clear cut as the ones with low frequency will obviously have smaller energy also.?


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    #8
    gotBass
    Registered Users Posts: 108 ✭✭gotBass


    looks like you need to examine in detail the duty cycle of the code, and see if optimisations can be made.

    X, are you using interrupts and the likes, or polling for certain conditions, there may be savings here also as you can got to sleep while waiting for an event. If you run the code on a slower CLK and adjust the timers/counters accordingly, you may save power.

    really it comes down to analyzing the frequency of occurrence of each function, deciding if it's possible to work using interrupts and then sleeping as much as possible.
    One more thing have you got all unused peripherals switched off?
    Some internal bits and pieces can be quite power hungry, in a micro.


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    #9
    Turbulent Bill
    Registered Users Posts: 1,622 ✭✭✭Turbulent Bill


    x in the city wrote: »
    Bill is right, hiver voltages and higher freq will use more power of course and complete tasks in a quicker time frame as opposed to lower voltages and slower clocks.

    I am wondering how I can go about getting an optimum value for a particular code function... Im not sure i understand how to go about this.

    I can calculate the energy in jules for different voltages/frequencies but this wont be clear cut as the ones with low frequency will obviously have smaller energy also.?

    A particular code function should take a particular number of clock cycles to execute. For example, if the function requires 11 million clock cycles, the device will take 1s to execute it running 11MHz, 2s at 5.5MHz etc. Multiply the power required for each frequency by the execution time to get the required energy, then compare the efficiencies of these. Very crude approach, but you get the picture.

    gotBass' suggestion is a good one. The number and type of functions required and the duty cycle of these could vary a lot, so you might need a metric for what you want to optimise the device for (e.g., maximum processing speed or minimum power usage).


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