A question regarding FRDM-K64F low-power modes and peripherals.

[peterfurey]

I'm developing an application prototype on a FRDM-K64F board. This application will want to maximize the low power features when in an idle state. My question is how do I deal with peripherals when the MCU is in a low-power state? For example, how should I minimize power consumption of the micro sd while in a low-power mode but still be up and running when I exit the low-power mode?

Thanks,

Peter

[Carlos_Mendoza · Accepted solution]

Hi Peter,

I would recommend you to take a look to the chapter 7.6 "Module Operation in Low Power Modes" in the reference manual. On this chapter there is a table that describes the functionality of each module in each of the low power modes:

http://cache.freescale.com/files/microcontrollers/doc/ref_manual/K64P144M120SF5RM.pdf

For example the SDHC module:

Here you can see that the module can serve as a wake-up source for the MCU when it is in "Stop" and "Very Low Power Stop" modes, the module is fully functional in "Very Low Power Wait" and "Very Low Power Run" modes, the module register states and associated memories are retained when in "Low Leakage Stop" mode and it is powered off when in "Very Low Leakage Stop" mode.

Hope it helps!

Best Regards,

Carlos Mendoza

Technical Support Engineer

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[peterfurey]

Thank you Carlos. When in doubt read the manual!

[mjbcswitzerland]

Hi Peter

Basically you need to control the clocks in the modes depending on which peripherals need to be able to continue to operate. Then you need to define the wakeup types - eg. do you need to be able to wake up on an external state change or a peripheral interrupt, or a wakeup event? Finally  you need to know whether the start-up time (transition from low leakage mode to RUN) is acceptable for each peripheral in question - eg. will the processor be ready to receive peripheral data that has started the wakeup  [for example, if a PLL has to restart and relock it will take a few hundred us whereas a free-running clock input that wasn't stopped will be much faster].

If you have external perpherals that consume power you need to consider whether you can power them down too (eg. using MOSFETs in their power lines) or whether you can command them to their own power saving modes before entering the processor's low leakage mode. Again the same types of considerations are also valid to the way and speed that the external periherals need to be restarted.

Here are a couple of K64F configurations that I have worked on to allow low power and fast responses:

K64 Low Power Mode Comparisons

Using Kinetis Low Power Stop Modes with unrestricted UART operation - a report

Reards

Mark

Kinetis: µTasker Kinetis support

K64: µTasker Kinetis FRDM-K64F support  / µTasker Kinetis TWR-K64F120M support  / µTasker Kinetis TWR-K65F180M support

LLWU: µTasker LLWU Support

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[peterfurey]

Thank you Mark, That was helpful.