WP7607 - services terminated and SSH connection lost with weak signal on GSM

I use a WP7607 with Legato 18.10.2 on a custom board with an external 5V power supply.
I create an SSH connection, and use the cm tool to switch on the radio and create a data connection.
The system gets registered to the home network and uses UTMS by default.

When I disconnect the antenna from the target board, after a while, all the Legato services get terminated and even the SSH connection gets disconnected.
l see following line in the logs:
le_mrc.c SignalStrengthIndHandlerFunc() 875 SignalStrengthIndHandler called with RAT.1 and ss.-91
So, this means that the system switched automatically from RAT UMTS(2) to RAT GSM(1), and then stopped working.

I can reproduce the same behaviour (apps terminated and SSH disconnected) when I execute the steps below:

  • create a data connection using UMTS via cm tool (antenna connected to the target board)
  • disconnect the antenna
  • force the RAT into GSM : cm radio rat GSM
    The system immediately terminates all services and the SSH connection gets lost

Could this be a power saving feature?
Why is the RAT going from UMTS to GSM when the signal gets too weak?
How can I avoid that the system stops working?


Hi @annaertd,

this is likely a fallback mechanism, where it eventually tries GSM as UMTS connection has been lost, and that doesn’t work out either.

You can select the RAT that you want to use using cm radio rat UMTS LTE for instance, and it should not try GSM.

BTW, when you mention an SSH connection, that connection is established over the cellular interface right?


the SSH connection is established over the USB cable between my target board and development PC.
I still wonder why the Legato system performs a shutdown when the GSM signal gets lost.
I expected that an application can keep on working during a period without 4G signal.


Oh I misunderstood the situation, yes that seems quite abnormal that it results in a shutdown.
I will try to reproduce it as well given your instruction.

If you happen to have some logs for us that would be even better, but it appears that something wrong is going on.
Also which modem version do you have (firmware release) ?


in attachment you can check my firmware versions (my legato framework is built with 18.10.2)
I performed the steps below to get a shutdown of my legato system.

I entered these commands in the terminal window of SSH connection (over USB cable towards target board):
log level debug
cm radio rat GSM UMTS

Then, I disconnected the antenna cable from my target board.
cm radio rat GSM

After a while the legato system stopped, and my SSH connection got disconnected.

log.txt (4.6 KB)