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Arm Mbed OS is a platform operating system designed for the internet of things
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Cellular PSM - Wake Module Provisions? #10737

Closed AGlass0fMilk closed 5 years ago

AGlass0fMilk commented 5 years ago

Description

@AriParkkila @mirelachirica

My team is working on using the PSM functionality of the ME910 cellular module (see driver PR here: https://github.com/ARMmbed/mbed-os/pull/10484). We have been attempting to use it with the mbed cloud client.

We are experiencing issues where Mbed's network stack loses/drops the PPP connection with the cellular module. We found an app note from Telit: Telit_ME910C1_PSM_App_Note_r0.pdf

that explains the cell module essentially goes into deep sleep when it enters PSM. We think this is likely the cause of the dropped PPP connection. To wake the module, you have to pull a power on pin low for 5 seconds and probably reinitiate the PPP connection.

My question is this: Does Mbed's cellular framework have provisions in place to handle this kind of behavior? If not, it seems like it would be a pretty common requirement of PSM-enabled designs (otherwise it would defeat the purpose of PSM). Therefore, the framework should support reinitializing the cellular module and PPP connection when a network request is made during PSM.

Issue request type

[X] Question
[ ] Enhancement
[ ] Bug
trowbridgec commented 5 years ago

@maclobdell

lauri-piikivi commented 5 years ago

hi, so far the PSM has been application controlled. App has the context that it can deep sleep the modem. App will also pause pelion cloud client. then the client must wake up the modem or modem wakes up on its own timer. In the case where this was done the modem did keep all state including the ppp. Wake up was automatic with low power uart.

this seems an area where there is some variation between modem implementations — lpuart or specific pins and differences in what state is kept over deep sleep. It would be good to understand if you run into ppp timeouts or is there some higher level protocol timeout that then fails as modem is in deep sleep. As stated we did not have this problem so it might be some higher level protocol periodic keepalive. Or did is a case where we need new ppp negotiation.

Ppp has some timeout definitions in https://github.com/ARMmbed/lwip/blob/master/src/include/netif/ppp/ppp_opts.h but to my understanding those have not been adjusted

trowbridgec commented 5 years ago

@lauri-piikivi I found section in the Pelion client documentation which follows what you're saying and looks promising: https://www.pelion.com/docs/device-management/current/connecting/device-guidelines.html#client-pause-and-resume

I'll report back how it works out for us.

Thanks for the tip!

AriParkkila commented 5 years ago

@trowbridgec That Pelion doc looks good. An application needs to disconnect before sleep and connect after wake-up:

  1. Shut down the network stack => NetworkInterface::disconnect(), also disconnects PPP
  2. Set up a network stack => NetworkInterface::connect()

Currently, it's up to the application to wake-up the modem before connect() and also if the modem tries to enter deep-sleep due to a longer period of network inactivity.

AGlass0fMilk commented 5 years ago

I think this has been addressed. Thank you!