I wouldn’t advocate omitting the Legato Application Framework from your system, but there are some technical options for setting up a data connection from the Linux core, outside the framework. Legato CM uses the RMNET interface for connectivity via the cellular interface, and you could potentially pull that support out of the framework (maybe) and implement it as a standalone application. It’s already there in the framework for free though, so I wouldn’t suggest this.
A simpler solution, which I’ve played with but which isn’t necessarily formally supported, is to use pppd for a DUN interface. With just the following effort, I can get a data connection in Linux:
Create a chat file in /etc/chatscripts/: (let’s call the file ‘test’)
ABORT 'BUSY'
ABORT 'NO CARRIER'
ABORT 'ERROR'
'' ATZ
OK AT+CGDCONT=1,"IP","apn.sierrawireless.com"
OK ATDT*99***1#
CONNECT
Use your APN for the CGDCONT command, and add any config you require for the connection.
Then call pppd to establish the data path:
pppd /dev/ttyAT connect 'chat -v -f /etc/chatscripts/test' defaultrouteThis should give you a ppp0 interface with connectivity.
This is simple, but it has drawbacks. Mainly, it will not use the hardware optimized data path that RMNET uses, meaning it’s less efficient in moving data from the cellular modem to the Linux core. It would also not be shareable with a host USB data connection (a feature coming in future FW releases, allowing a single connection to be shared between USB host and embedded Linux). If low effort and lightweight is important, this could have some utility for you. To take advantage of the benefits of Sierra system testing and design optimisations, using the Legato framework is the way to go in my opinion. Hope this helps 