Failed to Find /dev/ttyUSBx from Sierra EM7455

On Linux, you will need /dev/ttyUSB2 to communicate with EM7455 with AT commands and load EM7455 driver right.

For example, you might got the following result after entering sudo mmcli -m 0 if you have installed the same EM7455 module on Windows before and firmware.

  System   |            device: /sys/devices/platform/3610000.xhci/usb2/2-1/2-1.2
           |           drivers: cdc_mbim
           |            plugin: sierra
           |      primary port: cdc-wdm0
           |             ports: cdc-wdm0 (mbim), wwan0 (net)

Solution

• Find a x86 computer with Windows installed

• Put the EM7455 on x86 computer

• Install Windows EM7455 driver [link]

• Installed the below tools and make the COM ports of EM7455 could be found on device manager

3MB

SetUsbComp.zip

archive

Open

555KB

Sierra SetUsbComp Setting SOP.pdf

PDF

Open

• Put the EM7455 back to NRU series and the driver will be loaded properly

 System   |               device: /sys/devices/platform/3610000.xhci/usb2/2-1/2-1.2
           |              drivers: GobiSerial
           |               plugin: generic
           |         primary port: ttyUSB2
           |                ports: ttyUSB0 (qcdm), ttyUSB2 (at)

Cause

Some hard-wired configurations on EM7455 will be changed after Windows driver installed.

Reference

https://forum.sierrawireless.com/t/no-serial-ports-for-mc7304-after-fw-upgrade/9701