Exit from SNVS mode

[andrewkinmont]

We are having issues with getting our custom i.MX RT1051 board to exit SNVS mode using the wakeup pin, and wondered if this is an issue that might have been seen by others.

To test this, we are using the Power Mode Switch example application from the latest SDK. When we compile it for our board, we are able to exit from SUSPEND, but not from SNVS, using the wakeup pin. We have modified the code to also allow us to test wakeup using an SRTC alarm, and this works fine, which suggests that there is some issue with recognising the wakeup pin interrupt when the board is in SNVS mode.

We have also tested this same example application on our evaluation board, and it works fine (using the wakeup pin), however, our evaluation board is an older one that has the A0 step of the silicon, whereas our custom board has A1 silicon fitted.

Has anyone tested the Power Mode Switch example application on a newer evaluation board (one that has A1 silicon fitted)? This would probably eliminate the silicon revision as a possible source of the issue that we are seeing.

Thanks,

Andrew

[andrewkinmont]

Hi Kerry,

I have worked through the things that you have asked me to check. All of the tests have been performed on our custom hardware using the Power Mode Switch application as it is in the SDK. Here are the results:

1. The power consumption is falling to near zero when we enter SNVS mode. This means that the chip is definitely entering SNVS mode.

2. It is possible to exit SNVS mode using the ON/OFF pin, but the board does not restart using the WAKEUP pin.

   1) The WAKEUP pin is low for a second or more.

   2) There is no issue with the ON/OFF pin. The board is starting up using this without issue.

   3) When the board enters SNVS mode, the PMIC_REQ_ON goes low to turn off the external power supplies. It does not come high again when I assert the WAKEUP pin, but it does when I assert the ON/OFF pin.

3. The 32kHz oscillator is stable when the processor is in SNVS mode.

One thing I have noticed in the Power Mode Switch application is that the interrupt for the WAKEUP pin is configured as rising edge trigger, not active low trigger. This doesn't match the recommendation in the Reference Manual. We have tried modifying the application to active low trigger, but this doesn't seem to help.

Finally, we have previously had the processor exiting SNVS mode using an alarm from the RTC. This suggests that our issue has something to do with the processor recognising the interrupt on the WAKEUP pin to exit SNVS mode.

I have looked at the schematics for the evaluation board, and I notice that the only connection on the WAKEUP pin is to SW8. There are no external pull-up resistors, and no other connections to this pin. We don't have an external pull-up resistor either, however, we do have the Drain pins of two MOSFETs (BSS138P) connected to this pin to pull it low. Both of these are not switching during my testing (I have a shunt on the board to manually control the WAKEUP signal), but there will be a bit more capacitance on this pin compared with the evaluation board. This is likely to slightly increase the rise time on the WAKEUP signal. Could a slower rise time on this signal cause an issue? Is it worth testing the evaluation board by adding a capacitor to the WAKEUP signal?

I am sure we will work this out...

Best regards,

Andrew

[kerryzhou]

Hi Andrew,

  Thanks a lot for your test result and detail information.

   So, could you try to remove your two mosfets, then test it again? If you suspect the rise time, you also can add the capatcitor in the EVK board and test it.

  From the RM, 2 32KHZ cycle is enough to wake up in the WAKEUP pin.  But it didn't mentioned the rising time.

   These days, do you have any progress or updated information on your own board?

Have a great day,
Kerry

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[kerryzhou]

Hi Andrew Kinmont

  Thanks for your updated information.

  So, please compare the two schematic at first, any updated information, just let me know.

Have a great day,
Kerry

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[andrewkinmont]

Hi Kerry,

Just wondering if you have any more that you can offer regarding our issue with the processor not re-starting when we activate the wakeup pin. As I mentioned, there is no issue with the processor restarting from SNVS mode using an SRTC alarm, and we are also able to exit Suspend mode using the wakeup pin.

The only time there is an issue is when we use the wakeup pin to exit SNVS mode.

Any clues, or things we can test, would be very gratefully received.

Thanks,

Andrew