Using a secondary cf3 module


Hi all,

I’d like some information about using two cf3 modules in a mangOH board, for the following kind of scenario: the primary to provide a primary wan connection and the secondary connected to a different network with a different sim to act as a fallback. There’s a few things I don’t quite understand though.

The seconday cf3 slot only has the modem ( rf ) module connections, does that mean that it will appear to legato running on the primary as a second interface, so the primary would provide e.g. rmnet0 and rmnet1 ? If that’s the case, does it have a data profile index, so that the primary can configure and access it just like it can with the default data profile ?

In which case, what I’ve seen on the forum before, about connecting the mini sim to the secondary module either by changing the resistors r820 and r833 or though api commands, is that necessary ? Can a sim be “attached” to a second data profile corresponding to the secondary cf3?

If it isn’t like that and the mini-sim has to be routed to the secondary cf3 to activate it, would the apn have to be “pre-set” on the module ? This is where I’m confused, because only part of the secondary module is connected, what exactly is the way it’s supposed to be used ?

So, regarding connecting the mini-sim to the secondary module, I tried the gpioExpander build of mangOH for 16.10.3 and followed the instructions in this post but it doesn’t work: although the build is fine and mangoh runs pretty much without problems, no missing bindings or anything, setting gpioExpanderServiceGreen.mangoh_gpioExp2Pin7 ( U906_I07 ?) as a push-pull and activating it doesn’t appear to activate the secondary cf3 - but it does kill the usb connection to the mangOH, so it is doing something. Maybe I have it wrong, is that the right pin and how should it be set ?

thanks !


Your understanding is correct. the only issue with using the gpio expander is that since the secondary SIM slot doesnt have a SIM detect signal, it requires that the connection to the SIM be done at power up. So the gpio expander method will not work.
However, changing the resistors will.


thanks @asyal, that’s great. A follow-up question then is that to start a data connection on the secondary cf3, I’d need to do it through the services api using a second data profile index ? For example, using
le_mdc_StartSession( *profile_for_the_secondary_cf3 ) ? Does the framework know that the default data profile is for the primary module and another one is for the secondary ?