Troubleshooting and Recovery

Troubleshooting & Disaster Recovery

This guide covers emergency recovery procedures, common error diagnostics, and recovery methods for Qualcomm SDX55 modems running Fresnel.

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🚨 Emergency Recovery Procedures

1. Web UI Unreachable on Port 8080

If http://<modem-ip>:8080/ fails to load:

1. Test SSH Connectivity:

   ssh root@172.16.10.1

2. Inspect Running Processes:

   ps -ef | grep -E 'httpd|get_dashboard_data|simpleadmin'

3. Check Supervisor Logs:

   cat /tmp/simpleadmin_daemon.log

4. Manual Restart:

   pkill -f 'httpd.*8080'
   pkill -f 'get_dashboard_data.pl'
   pkill -f 'simpleadmin_daemon.sh'
   
   nohup /usrdata/simpleadmin/scripts/simpleadmin_daemon.sh >/tmp/simpleadmin_daemon.log 2>&1 &

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2. Clearing Stuck Serial Ports (/dev/smd7)

If AT commands time out or error with Device or resource busy:

1. Check for stale lock files:

   ls -la /var/lock/doAT.lock

2. Remove stale lock files:

   rm -f /var/lock/doAT.lock

3. Terminate stuck Perl or Python processes holding the serial interface:

   fuser -k /dev/smd7 2>/dev/null || true

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3. Emergency Baseband Reboot (RF Cycle)

If the modem loses network registration and fails to re-attach after band switching:

• Soft Baseband Restart (Fastest):

  /usrdata/simpleadmin/scripts/doAT.pl 'AT+CFUN=1,1'

  This reboots the cellular DSP while keeping the embedded Linux host OS running.
• RF Radio Toggle:

  /usrdata/simpleadmin/scripts/doAT.pl 'AT+CFUN=0'
  sleep 3
  /usrdata/simpleadmin/scripts/doAT.pl 'AT+CFUN=1'

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4. Restoring Default Band Locking

If you locked the modem to bands not supported by the local cellular tower, the modem will disconnect and stay unregistered.

To reset band masks to factory defaults:

# Reset LTE band mask to all bands
/usrdata/simpleadmin/scripts/doAT.pl 'AT+QNWPREFCFG="lte_band",1:2:3:4:5:7:8:12:13:14:17:18:19:20:25:26:28:29:30:32:34:38:39:40:41:42:43:46:48:66:71'

# Reset 5G NR band mask to all bands
/usrdata/simpleadmin/scripts/doAT.pl 'AT+QNWPREFCFG="nr5g_band",1:2:3:5:7:8:12:20:25:28:38:40:41:48:66:71:77:78:79'

# Restore Automatic Network Mode
/usrdata/simpleadmin/scripts/doAT.pl 'AT+QNWPREFCFG="mode_pref",AUTO'

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🌐 Network & IP Addressing Conflicts

Subnet Collision

If your upstream Wi-Fi router also uses 172.16.10.x or 192.168.225.x, routing conflicts will occur:

• Symptom: Host can access the modem web GUI, but internet traffic fails to route through the cellular link.
• Solution:
  • Check your host's active route table:

    # Linux/Mac
    netstat -rn | grep default
    # Windows
    route print

  • Ensure only one default gateway exists, pointing to the modem interface.
  • If necessary, adjust the upstream router's LAN DHCP subnet to 192.168.1.x or 10.0.0.x.

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☁️ Troubleshooting Cloud Telemetry Pushes

If the cloud dashboard does not show incoming telemetry:

1. Verify Modem Internet Connectivity:

   ping -c 3 8.8.8.8

2. Verify DNS Resolution:

   nslookup api.telegram.org

3. Test Manual Push:

   /usrdata/simpleadmin/scripts/telemetry_pusher.sh

4. Check Configuration: Inspect /usrdata/simpleadmin/config/telemetry.conf to confirm:
   • SERVER_URL is formatted properly (including protocol https:// or http:// and port 8000).
   • AUTH_TOKEN matches the token defined in the cloud server's .env file.

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