EM7455 /dev/ttyUSBX device files

IoT Modules
1

There are 3 ttyUSB (interface 0, 2 and 3) devices files created by the GobiSerial driver on Linux.

What is the purpose each of these device files?

/: Bus 06.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 5000M
|__ Port 1: Dev 2, If 0, Class=Vendor Specific Class, Driver=GobiSerial, 5000M
|__ Port 1: Dev 2, If 2, Class=Vendor Specific Class, Driver=GobiSerial, 5000M
|__ Port 1: Dev 2, If 3, Class=Vendor Specific Class, Driver=GobiSerial, 5000M
|__ Port 1: Dev 2, If 8, Class=Vendor Specific Class, Driver=GobiNet, 5000M

2

They are DM, nmea, AT port

3

What is the use of DM and nmea?

Please confirm if they are enumerated incrementally or the order does not matter.
In other words,
ttyUSBn for DM
ttyUSBn+1 for nmea
AT for ttyUSBn+2

Please confirm that the interface numbers are consistent.

4

you can check if AT command port is having response on ttyUSB2
you can check if there is NMEA frame in ttyUSB1 when AT!GPSFIX.

5

They enumerate incrementally unless a process is holding open a file descriptor with the path the driver wants. In that case it skips that number. For example if you reset the device while you have ttyUSB2 open, there will be a hole between ttyUSB1 and ttyUSB3. All the tty nodes after USB2 will be shifted up by one.