I'm developing some communications software that uses a CDMA modem over a USB connection to provide internet services for an embedded Linux device. The software also needs to monitor the modem status via AT commands without interrupting internet service on the device. I'm still in the exploration stages of this project and haven't really gotten into the meat of the coding yet, so for now I've just been playing around with the modem driver, pppd, and minicom on an Ubuntu laptop. Eventually when I develop the software, pppd will be running in the background and I'll be using libcurl to do HTTP gets/etcetra, and I'll want to write/read AT commands directly without the use of minicom.


The problem I have right now is that pppd and minicom can not run concurrently because they are both trying to access the same device file (/dev/ttyUSBModem0). The modem manufacturers, however, told me that the modem would be able to handle internet connectivity and AT commands concurrently.


I've read through what little documentation exists for this USB serial modem driver and it says that the modem has three interfaces: DATA channel (used by the modem driver, for pppd), ETS channel (for debugging), and the AT MUX channel (for AT commands). I'm a little shaky here...how would I access one USB interface on the same device versus another? Should there be a different device file created for each interface?



The main questions I'd like to ask are:

1) Is it indeed possible to use both pppd and minicom simultaneously on the same USB serial modem device?

2) With my USB device plugged in, how would I access one interface over the other? Is that something that the modem device driver should provide for?

3) How would I send AT commands to the modem and receive the results without the use of minicom? Do I just open the /dev/ttyUSBModem0 for read/write privileges? (That probably won't work though since pppd will already be accessing the device file).


Thanks for any help you can give me so I can get on the right track.