K82 : change power modes RUN <-> VLPR

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K82 : change power modes RUN <-> VLPR

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EugeneHiihtaja
Senior Contributor I

Hello !

SDK example clearly demonstrate how power mode should be changes.

But it is not clear what kind of manipulation should be done for re initialization of peripherals  becouse clocking scheme might change.

For example in case of I2c/UART it might need full initialisation for be able to keep the same baudrate becouse clocking frequency can change ( depends from clock source ) and new divider should be calculated.

Some peripherals like LTC,TRNG use bus/system clock and if I understand peripherals  itself should be disabled/enabled for moment of transition even it is not used while transition.

Is any Application note and other recomendations  exists for   handle RUN<-->VLPR transit ?

Regards,

Eugene

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4 Replies

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jingpan
NXP TechSupport
NXP TechSupport

Hi Eugene,

Please read AN4503 for power management. Different devices and different peripheral has different requirement. Yes, some times there isn't low power working example for each peripheral. You have to adjust the clock and settings according to RM.

Regards,

Jing

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EugeneHiihtaja
Senior Contributor I

Hi Jing !

It is clear situation about actual code what should be used to switch between modes.

But should I do something with peripherals what clocked directly from System/Bus clock.

If clock is change to 120 to 4Mhz they should continue to run with lower performance ( for example LTC, TRNG, QSPIO)

or for avoid any stall situation I should disable/enable peripheral ( or their clock) while transition to/from ?

Regards,Eugene

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456 Views
jingpan
NXP TechSupport
NXP TechSupport

Hi Eugene,

I think to those communication and timer peripherals, if their clock source is system/bus clock, you should change their clock setting. For those peripherals like LTC or TRNG, you needn't change clock setting. They are not timing sensitive.

Regards,

Jing

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EugeneHiihtaja
Senior Contributor I

Hi Jing !

So all peripherals what are clocked from System/Bus clock , no need any attention if they able to work with reduced clock.

Their internals easy adopt any clock if it in expected range.

Others might need to change clock source and require full reinitialization for keep own clock at expected value, for example I2C should continue with 100Khz speed.

Regards,

Eugene

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