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    Resolving SIM Card Detection Issues with Fibocom L850-GL Modem on ThinkPad X1 Carbon Running Linux

    By h0ag's avatar h0ag | On | 968 views

    Resolving SIM Card Detection Issues with Fibocom L850-GL Modem on ThinkPad X1 Carbon Running Linux

    Introduction

    The ThinkPad X1 Carbon 6th Generation comes equipped with a Fibocom L850-GL LTE modem, enabling mobile broadband connectivity. However, users running Arch Linux (and others) may encounter issues where the modem fails to detect the SIM card, rendering mobile connectivity unusable. This article delves into the problem and provides a step-by-step solution to restore SIM card functionality.

    Problem Description

    Hardware and Context:

    • LTE Modem: Fibocom L850-GL
    • Laptop: ThinkPad X1 Carbon 6th Gen
    • Tested Operating Systems: [Arch Linux, Alma Linux]

    Symptoms:

    • The modem is recognized by the system, but the SIM card is not detected, despite being correctly inserted and functional in other devices.
    • ModemManager logs indicate errors such as the SIM being "missing" or AT command failures due to timeouts.
    • System logs (dmesg) display recurring errors on ports wwan0at1 and wwan0at0, with timeouts occurring when sending AT commands like ATI3.
    • The modem transitions through states: "unknown" → "locked" → "failed," attributed to the perceived absence of the SIM card.

    Analysis

    The issue appears to stem from a communication breakdown between the system and the modem, specifically concerning the SIM card interface. Timeout errors during AT command execution suggest that the serial ports associated with the modem may be blocked or improperly configured, hindering effective communication. This could result from software misconfigurations, driver issues, or conflicts within the serial interface management.

    Solution

    To address this problem, follow these steps:

    1. Install the xmm7360-pci Driver:

    The Fibocom L850-GL modem requires the xmm7360-pci driver for proper operation. Ensure that this driver is installed on your system. You can obtain it from the xmm7360-pci GitHub repository.

    bash
    git clone https://github.com/xmm7360/xmm7360-pci.git
cd xmm7360-pci
make
sudo make install
    1. Load the Driver and Open the Data Channel:

    Before executing the python script, stop the ModemManager service with sudo systemctl stop ModemManager.

    After installing the driver, load it and open the data channel to facilitate communication between the modem and the system.

    bash
    cd path/to/xmm7360/
sudo python3 ./rpc/open_xdatachannel.py --apn YOUR_APN
    1. Restart ModemManager:

    With the data channel open, restart the ModemManager service to apply the changes.

    bash
    sudo systemctl restart ModemManager
    1. Verify SIM Card Detection:

    After restarting ModemManager, check if the SIM card is detected by the modem. Use the following command to inspect the modem's status:

    bash
    mmcli -m 0

    Ensure that the output indicates the SIM card is present and recognized.

    Conclusion

    The Fibocom L850-GL modem on the ThinkPad X1 Carbon may experience SIM card detection issues under Arch Linux and others due to blocked or misconfigured serial ports. By installing the appropriate driver, opening the data channel, and restarting ModemManager, you can resolve these communication barriers and restore mobile broadband functionality. This solution has been effective for users facing similar challenges.

    Additional Resources

    Made by h0ag