SIM7070G firmware upgrade not detected as COM port via USB pads on TTGO T-SIM7070G

[Shadowfader]

Hello Espressif community,

I am currently working on a project using the **LilyGO TTGO T-SIM7070G** (ESP32-WROVER version with SIM7070G modem) to send sensor data via LTE-M/NB-IoT. I encountered a significant issue with performing a firmware upgrade on the SIM7070G modem using the USB pads on the board.

**Board and hardware details:**

* Board: LilyGO TTGO T-SIM7070G (ESP32-WROVER)
* Modem: SIM7070G
* PN Number: S2-108HK-Z30YE
* Current Firmware Revision: 1951B14SIM7070
* USB breakout connected to the modem pads

**Steps performed for firmware upgrade:**

1. Soldered a USB breakout to the four USB pads of the SIM7070G module.
2. Connected the modem to the PC via USB.
3. Installed all required drivers. The device is recognized by Windows as a connected device.
4. Verified modem communication via AT commands:

```
AT
OK

AT+CGMR
Revision: 1951B14SIM7070
OK
```

**Problem encountered:**

* Despite the USB connection working and drivers being installed, the modem **does not appear as a COM port** in Windows Device Manager.
* The firmware upgrade tool requires the modem to be detected as a COM port in order to proceed.
* Because the COM port is not created, the upgrade cannot be performed.

**Context and reason for firmware upgrade:**

* The SIM7070G modem has an internal TCP/IP stack bug that causes crashes after 2–3 consecutive TCP connections in the same firmware session.
* This bug prevents stable data transmission for applications such as MQTT, UDP, HTTP, or raw TCP.
* Currently, the only reliable workaround is to perform a **hardware power cycle** after every message to reset the modem completely.
* I am attempting the firmware upgrade to see if a newer revision of the SIM7070G firmware resolves this TCP/IP stack issue.

**References used for upgrade procedure:**

1. [SIM7000 ESP32 firmware upgrade guide (GitHub)](https://github.com/Xinyuan-LilyGO/LilyG ... upgrade.md)
2. [T-SIM7000G firmware update guide (GitHub)](https://github.com/Xinyuan-LilyGO/LilyG ... irmware.md)
3. [YouTube tutorial](https://www.youtube.com/watch?v=lGctqLDGHz4)

**Questions for the community:**

* Is there a specific USB mode, driver, or initialization step required to make the SIM7070G appear as a COM port when connected via the USB pads?
* Has anyone successfully performed a firmware upgrade using the USB pads on a TTGO T-SIM7070G, and if so, what steps were required?
* Are there alternative methods to safely update the SIM7070G firmware without risking the module?

Thank you very much for any guidance, insights, or shared experiences. This issue is critical for enabling stable LTE-M/NB-IoT communication in my project.

Best regards,