iMX7S low power management

[kunjalgarach]

We are using iMX7S processor in wearable medical device development were power consumption is primary factor.

Our use case is M4 is always in RUN mode and A7 in STOP mode. Whenever I need to do some processing on A7, M4 sends weak-up request to A7, A7 do some processing and go in to STOP mode again.

To check iMX7S power consumption I am measuring current on VDD_ARM and VDD_SOC power rail.

A7 Mode	M4 Mode	Current mA VDD_SOC	Current mA VDD_ARM
RUN	RUN	174.8	8.4
MEM	RUN	175.9	3.3

As you see from this table. If I put A7 in STOP mode, VDD_SOC current is almost same while VDD_ARM current is decrease.

So the power consumption of iMX7S in A7 in STOP mode and M4 in RUN mode is around 180mW. 

So how to reduce power consumption when A7 is in STOP mode and M4 is in RUN mode?

Kunjal

[harish_g]

Hi ,

This a question based on your question . How did you put A7 core to STOP while allowing M4 core to be in the RUN mode ? We are trying to acheive exactly this , but have had very little success . Is there any patch that you can post here , that will acheive this configuration ?

Again , for your scenario , Did clockgating each peripheral in Fastmix/Megamix domain reduce any power ? It will sure increase time for recovery , but that seems like a valid option . There is a bit in the register TARGET_ROOT of every peripheral's clock root , 'Enable' . Does that actually power down the device ( as in gate the clock  )?

Regards ,

Harish Ganesan . 

[igorpadykov]

Hi Kunjal

M4 belongs to SOC power domain so seems it can not be significantly
reduced, please check Figure 5-9, 5-10. Power Domains,
Table 5-5. Low Power Mode Definition i.MX7S Reference Manual
http://cache.nxp.com/files/32bit/doc/ref_manual/IMX7SRM.pdf

Best regards
igor
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[kunjalgarach]

Hi Igor,

Thanks for your reply.

For battery operated wearable medical device power optimization is very critical.

I studied the document you suggested (Point 5.5.5.1) and found that we need to control power through Power Gating Control (PGC).

As M4 is a part of Fastmix and Megamix (PGC_MF) power domain and doesn't have its own PGC, So that If M4 core is in RUN mode all the time PGC_MF power domain can not be power down.

Is there any configuration/method possible by which I can able to switch off the peripherals of Fast/Mega mix power domain other then M4.

Best Regards,

Kunjal

[igorpadykov]

Hi Kunjal

Table 5-3, Table 5-4. Power Mode shows all available options.

Best regards
igor

[kunjalgarach]

Hi Igor,

Table 5-3 and 5-4 summarizes the external power supply state in all the power modes.

I am taking about internal Power Gating Control (PGC) which controls the power up/down of individual subsystem. PGC Power domain (5.5.5.1).

Best Regards,

Kunjal

[igorpadykov]

Hi Kunjal

there is no configuration/method to switch off the peripherals of Fast/Mega mix power domain

other then M4, it is stated in sect.5.5.7 Power control for the M4 Platform :

"M4 LPM is same as A7 LPM. M4 platform doesn’t have its own power domain and exist
as a part of Megamix."

Best regards
igor