[WP8548] Using it without legato


#1

I am currently using WP8548 and MangOH Red with default firmware, I need to have 3G (GPRS) connectivity and I managed to get that working with the cm radio/cm data commands. Those commands are part of the Cellular Modem tool/app that comes with legato, which is by default built into default WP8548 firmware.
I am interested if this can be done with WP8548 without legato framework? I will be running pure yocto and I would like to achieve somehow to have 3g connectivity there. Is there any similar tool, special drivers or anything like that?


#2

Err … GPRS is not 3G - it’s 2G (or, perhaps, “2.5G”)

What do you mean by that?

Yocto is not something you run on the target - it’s a tool you use in creating the thing that you run on the target:


#3

I apologize for misunderstanding and my wrong wording.
What I want to achieve is to have 3G connectivity without Legato framework (I use advanced C++ applications that can no be supported by Legato), how can I can achieve this? I guess I need userspace application that handles 3G modem kernel driver? What else?


#4

I would appreciate if someone would help me by answering my questions.
Thank you in advance


#5

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' defaultroute

This 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 :slight_smile:


#6

I have the same problem as @lazzox, but on a wp7702, and while the ppp solution suggested by @rkirk worked, it is kind of a lo-fi solution, plus it blocks the modem from further calls, which I believe a rmnet/QMI solution does not.

I’ve seen lots of other people using Qualcomm based modems getting a /dev/cdc-wdm0 and similar, and then one can use more or less standard tools to use it as a regular network device (e.g. wwan0). It would be awesome if that was possible with these chips as well. Thanks.