MangOH Yellow - time/date doesn't persist with ulpm

Hello everyone,

I am hoping this isn’t a re-post, but I did not see anyone else report this issue I am noticing; so here it goes… When configuring the MangOH Yellow for ulpm it appears that after a ulpm cycle the system’s date and time do not persist. Instead I see that the date and time revert back to January 6th 1980. Additionally I noticed this issue also appears to occur if the device loses power abruptly (removing the USB cable while the device is on).

Does anyone know if there is a solution to getting the date/time to persist after a ulpm cycle? For what I am using this board for this is kind of a big deal if there is no solution. I didn’t see anyone else report this issue here, so I hope I am not alone here.

If anyone has any ideas/solutions I would greatly appreciate the help!

Thanks in advance!

Legato Version: 19.10.1
Low Power Manager Firmware Version: 002.013

Hi Steffono. I have seen the same thing with our system: WP77xx with custom hdw. My interp is that in achieving ultra low power consumption the choice was made not to keep a clock running. In my system, one of the early steps of a power-up after ULPM is to get in touch with the time/date server and re-establish the clock. So the only way to tell that the clock was ever wrong or off is to look at the beginnings of the log for that power-up.
If your system doesn’t quickly re-establish the correct time, it probably means that the stored uri for the time/date server is not properly saved. Others might chime in on where that is located.

You should be able to save time on yellow even in ULPM.
Have you looked at:

@Zahid can you provide insights to @jdots83

Hi @steffono/@jdots83,
mangOH Yellow has a: clock/calendar
on-board. As long as the rtc-pcf85063 & rtc_sync kernel modules are built-in the yellow.sdef and you
have a battery with juice supplying power to the PCF85063TP you should be fine. rtc_sync updates the PCF85063TP @ 10secs. - you can shorten the 10 secs., if you need more accuracy. Note the
WP77 cell side has its own timekeeping & clock for the modem processor and that can also be used, but I’m not sure on the details of that.


Hello Zahid,

I appreciate the help you and @jdots83 were able to provide! This greatly helped me and my colleagues to make some decisions on how to proceed with our project!

I have one more question if you are able to help. I am doing different tests with low powermode and I am having trouble trying to confirm whether or not if an application will still run even when the device is in this state.

Are all applications besides those critical to the device’s function in ULPM shutdown when in this state, or could I still run a custom application even when the device is “sleeping”? For example, if I am running a program when the device is in normal operation and then the device transitions to low power mode , will that kill my program?