Modem PSM cycle separate to CPU sleep

[Nevera]

Hi all,

I've been recently working on PSM for my device, and I've not found any resources that answer my query or provide the knowledge I need.

From my reading in this article, #6.1.
Its suggested that a device can request a long TAU, and make a request to the network during this period. (Below Figure 2).

Ultimately, this is the exact flow I'm looking to implement, but it would require the processor to wake (every hour in my case) to make a reading from it's sensors, whilst the modem has a longer TAU (24 hours). If a certain criteria is met during the processor's hourly wake, it should send that data regardless of the pre-negotiated PSM settings.

I've read in a response to this post from Bjorn that the modem PSM cycle is tied to the power states described here.

Ultimately, I understand that the modem operates asynchronously to the processor, but I'm unsure if I'm able to explicitly have the processor process and sleep on a different cycle to the modem's PSM.

Sorry if this is a little unclear or misguided, its all a learning experience!

Thanks!

[Carl Richard]

Hello, Nevera!

Thank you for the question! You are not the only one that is confused by this. Your desired behavior is indeed possible as the modem does operate separately from the processor. I.e. the modem won't wake from PSM before the process explicitly tells it so or the timer runs out. However, as Bjørn says you will not be able to enter the "System-Off" mode and still stay connected to the network, but I believe PSM should be adequate.

You should take a look at this blog post and this blog post, which both describes how to achieve low power operation using PSM. The example code from the former uses a transmission timer that is set to the same as the PSM interval, but that timer can be changed to any desired value (and you can request a much longer PSM timer). 

Hope this helps and do say if you need any more help!

Best regards, 
Carl Richard