Bruno De Paoli

Radio control and data interfaces over USB

Discussion created by Bruno De Paoli on Aug 1, 2012


I am using a GSM modem in an EC7 platform over USB interface. The plan is to use the standard CE RIL layer to present standard radio services to the application.

The modem presents 3 interfaces over the one USB port ( i.e. 3 interface descriptors)

  • CDC Data
  • Application specific for firmware upgrade

My understanding is that one of these interfaces is for data and one for control which suggests we do not need the mux07 layer that normally multiplexes control and data over the one serial interface. The plan would be to use the standard winCE USBSER driver to provide the virtual comm port. I believe we need one driver per USB interface descriptor and so would use a USBSER driver instance per interface giving us multiple virtual comm ports for the upper layers.

I have seen conflicting information on this, in some cases suggesting we still need the mux layer even over USB. To me this does not make sense since USB already provides us with separate interfaces in the first place.

Can anyone clarify if the mux layer is needed in this case (i.e. USB)? Has anyone implemented this?