I've been trying to talk to a 3G modem using MQX3.8 with the cdc_serial demo.
The trouble that I have been having is that after the modem is attached, the data interface is selected. I want to select the control interface so that I can issue AT commands to the modem. Here is what I get from the console when the modem is attached:
----- CDC control interface attach Event -----
State = attached Class = 2 SubClass = 2 Protocol = 1
----- CDC data interface attach event -----
State = attached Class = 10 SubClass = 0 Protocol = 0
----- CDC control interface selected -----
----- Device installed -----
----- CDC data interface selected -----
At this point, the example code then issues an "fopen()" to "tty0:" which translates to a "_io_cdc_serial_open()". As far as I can tell, I need to select the control interface with "_usb_hostdev_select_interface()" before using fopen() as it is only possible to select one interface at a time - once the data interface is selected I cannot talk to the control interface. Have I got this right or have I missed something? Anyway, doing this causes exceptions or unhandled interrupts.
Incidentally, the data interface of the modem does not echo characters back. I'm not surprised at that but I notice that the demo description seems to infere that I should get echo's "straight out of the box" so to speak.
I'd appreciate any help here or at least confirmation that I'm on the right track.