SRTC on IMXRT1051

[mali]

We want to implement the RTC clock in a new project with the IMXRT1051 processor using Keil MDK. We already found the SNVS examples which show how to activate the SRTC. SRTC is now running but the power consumption is about 60uA which is too much. Has anyone else used the SRTC and has a smaller power consumption? In SNVS there are also general purpose registers named SNVS->LPGPR which I would need to save some bits for the SRTC, but we are not able to write on it (GPR_SL and  GPR_HL are low and we are in privileged mode). Does anyone have a sample code in which the LPGPR can be written? Thanks

[Yuri]

Hello,

  Perhaps the problem concerns using debugger in order  to write the register.

  "To R/W the LPGPR registers through the debugger, the GPR_Z_DIS bit needs to be set in the LPCR register.

When the debugger is used, the SNVS issues a security violation and zeroizes the GPR registers. The GPR_Z_DIS

bit needs to be set to keep the LPGPR registers from being zeroed.

   The LPGPR registers are privileged access R/W. If needed, non-privileged software can access the LPGPR registers

by setting the NPSWA_EN bit in HPCOMR. The HPCOMR is accessible by privileged software.

  For more details on the SNVS,  customers may refer to the RM and the SRM Security Reference Manual for the i.MX RT1050 Processor (requires licensing agreement)."

https://www.nxp.com/docs/en/reference-manual/IMXRT1050RM.pdf 

Have a great day,

Yuri

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[mali]

Hi Yuri,

you were absolutly right. The problem was that GPR_Z_DIS needed to be set to be able to write to the GPR registers.

So there is only the remaining question, why is the powerconsumption so high (~60µA).

Concerning to datasheet IMXRT1050IEC Rev. 1, 03/2018 chapter 4.3.4.2 OSC32K, it should be possible to deactivate the ring oscillator and so reduce the power consumption to about 6,5µA which would be tolerable for us. The question now is how do we deavtivate the ring oscillator? Is it possible to reduce the power consumption to 6,5µA?

Thanks in advance.

Best regards

Martin

[Yuri]

Hello,

  According to Table 5 (Low power mode configuration) of app note AN12094
(Power consumption and measurement of i.MXRT1050, Rev. 0, 11/2017)

only (external) RTC32K clock is applied in so called SNVS mode.

  Also, AN12085 (How to use iMXRT Low Power feature) may be useful.

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

https://www.nxp.com/docs/en/application-note/AN12085.pdf 

Software:

https://www.nxp.com/docs/en/application-note-software/AN12085SW.zip

Regards,

Yuri.

[kunyichen]

where can download AN12085SW.zip

the link is broken

Software:

https://www.nxp.com/docs/en/application-note-software/AN12085SW.zip

[mali]

Hi Yuri,

thank you for your reply!

We read through all datasheets, but couldn't find any hints to solving our problem.

Fact is that the power consumption on RTC is too high. At the moment the current is about 60µA and discharges the supercap in about 1 hour. If there is no possibility to reduce the power consumption of the RTC, the internal RTC is useless for us and we need to assemble an external RTC.

Maybe someone other has a solution concerning my problem?

Best regards

Martin

[Yuri]

Hello,

  In SNVS (RTC) power mode all power supply voltages on board (except

VDD_SNVS_IN ) should be off. VDD_SNVS_IN (3.3 V) current in such case

is about 20uA (with Tamper detection disabled).

  Perhaps external RTC is needed to improve situation.

Also i.MX 7ULP may be considered. But it is not launched yet.

Regards,

Yuri.