Understanding power modes

[rans]

Hello,

I haven't find a lot of information about power modes in iMX RT1050 reference.

I did find the following application note:

https://www.nxp.com/docs/en/application-note/AN12094.pdf 

It list a table with definition for each run mode and low power mode ( I assume from this that run mode is just a higher power mode , Right ?)

Yet, I don't understand: 

Is it that this conditions were randomly named as given in table "suspend" , "snvs" (not related to any hardware state) ?

Or is that cpu transfer itself to hardware state when the required power conditions are met as mentioned in the table ? 

How can we verify that the cpu got into the power mode that we wanted ? Is there a register which states what power mode the cpu is right now (or any statistics about transitions between power modes) ?

Thank you,

ranran

[igorpadykov · Accepted solution]

Hi ranran

detailed description of low power modes can be found in

AN12085 How to use iMXRT Low Power feature
https://www.nxp.com/docs/en/application-note/AN12085.pdf

Best regards
igor
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[rans]

Hi Igor,

Thank you very much for the documentation, it is very helpful.

I read it, but there is still something that I don't understand:

The document state how to enter a state and how to exit from state.

From my understanding , the exit steps are done in order to exit from the power mode to run mode.

1.

    How can we know for sure that we entered a required power mode state ? I mean maybe we forgot to power of a pll or clock , how do we know that the mode was changed or not ?

2. In reference it says " IDLE mode is entered automatically from RUN mode when CPU
executes WFI instruction, " , but in this application note, it gives a long list of required steps in the entry diagram. So is it that only WFI is required or do we also need to power off modules as listed in this AN ?

3.

What happens if we entered system idle mode, and then got timer interrupt and doing something in busywait after the interrupt ? Is it that we moved to another state (not "system idle" mode) ? But we haven't done the exit steps described in the doc, so I am not sure what state we are in such case.

Thank you,

ranran

[igorpadykov]

Hi ranran

one can check that processor entered low power mode by measuring its power

consumption or for example output some clock using CCM_CCOSR register and

sect.18.7.21 CCM Clock Gating Register 0 (CCM_CCGR0) i.MXRT1050 Reference Manual.

Any unmasked interrupt will cause processor to exit from low power mode.

Best regards
igor