I have a SIM7100E modem running on 4.8.0-26-generic which specifies the following devices:

/dev/ttyUSB1 : NMEA port for GPS NMEA data output
/dev/ttyUSB2 : AT port for AT commands

Connecting to ttyUSB2 works fine, I can turn on/off GPS engine etc. But ttyUSB1 does not produce any output data. There does not seem to be anything wrong with the GPS, because we can do

$ microcom /dev/ttyUSB2

which is a command that configures what sort of GPS NMEA data to output. The above example means "report everything once every second". This works, but the problem is that using this command, the output gets piped to ttyUSB2 and not ttyUSB1, which is perpetually empty.

I'm wondering why this happens and what configurations are necessary to get the GPS data piped to ttyUSB1.

Linux manual and AT command set

I should note that the Linux configuration steps outlined in the were based on installing a module called GobiSerial -- I suppose this is where the configuration happens, but installing GobiSerial didn't work.

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