you can stream the gps NMEA sentences through one of USB serial interfaces .We have a guide in draft.. ill get it published in the next few days.
In summary, this is what you need to do.
Connect to the second interfaces on the GSM module;
minicom -b 115200 -o -D /dev/ttyACM1
Activate storing of last values of NMEA, from the GPS to the GSM module;
AT+UGRMC=1 AT+UGGLL=1 AT+UGGSV=1 AT+UGGGA=1
Activate the unsolicited aiding result.
Set NMEA data to to stream through USB interface /dev/ttyACM3
Turn on GPS, (Start GNSS with GPS+SBAS+GLONASS systems and local aiding.);
To view the stream
minicom -b 115200 -o -D /dev/ttyACM3
To stop GPS, use
We have some info here about the UGPS command which is used to turn on GPS.
This document describes these all these commands in detail.
I hope this is what you are after
Mark --OzzMaker.com --