> For the complete documentation index, see [llms.txt](https://docs.cubepilot.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.cubepilot.org/here-4/recovering-the-firmware.md).
# Recovering the Firmware
This section explains how to resolve firmware-related issues.
Recovering the firmware may be necessary if a firmware update fails or incompatible firmware is loaded. Attempt flashing the bootloader via the SWD port if the Here4 LEDs are solid white.
## Prerequisites
The following information is for J-Link devices, but it can also be applied to similar devices when using an ST-Link.
* J-Link device:
* [EDU Mini](https://www.segger.com/products/debug-probes/j-link/models/j-link-edu-mini/) V2, for personal/educational use (and an adapter board)
* [BASE Compact](https://shop.segger.com/debug-trace-probes/debug-probes/j-link/j-link-base-compact), for commercial use
* Pinout:
* **6-pin JST SUR** plug for SWD port
* Refer here for SWD port pinout: [FMU Debug pinout](https://docs.cubepilot.org/user-guides/autopilot/the-cube/introduction/interface-specifications#fmu-debug)
* Download and install “J-Link Software and Documentation Pack” from [segger.com/downloads/jlink/](https://www.segger.com/downloads/jlink/)
* Download the bootloader file for your flashing tool:
* JLink: [Here4\_bl.hex](https://github.com/CubePilot/GNSSPeriph-release/raw/refs/heads/release/bootloaders/Here4_bl.hex)
* STLink: [Here4\_bl.bin](https://github.com/CubePilot/GNSSPeriph-release/raw/refs/heads/release/bootloaders/Here4_bl.bin)
* De-cased Here4
* Remove M3 bolt (2 mm hex head)
* Gently separate the two housing parts, using a plastic tool to pry the clips apart
* Images for reference:
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## Procedures
### J-Link with J-Flash Lite
1. Plug Here4 into CAN port of a Cube (for power).
2. Plug J-Link into the SWD port on the Here4.
3. Connect J-Link to PC over USB.
4. Open **J-Flash Lite** (JFlashLite.exe).
5. Use the following parameters:
6. Click **OK**.
7. Plug the Cube into power, power up the Here4, and click **Erase Chip**.
8. Click the button under Data File and open the **Here4\_bl.hex** file.
9. Click **Program Device**.
10. Check the log for the following output:
11. Unplug the power and SWD connections.
12. Plug in Cube, connect to Mission Planner and verify Here4 shows up in DroneCAN (in **MAINTENANCE** mode).
13. Update the Here4 (**Menu** -> **Update** -> **Yes, search the internet for updates**).
14. Verify Here4 shows up in **OPERATIONAL** mode.
## Connect Programming Devices
This section contains the pinout on either side to assist in connecting the J-Link or ST-Link device to the SWD port. The **same pinout is used for J-Link and ST-Link devices** with 20-pin connectors.
Solder or crimp the 6-pin JST SUR wires onto 2.54 mm female header plugs (if using programming devices with header pins).
3. Connect J-Link to PC over USB.
4. Open **J-Flash Lite** (JFlashLite.exe).
5. Use the following parameters:
6. Click **OK**.
7. Plug the Cube into power, power up the Here4, and click **Erase Chip**.
8. Click the button under Data File and open the **Here4\_bl.hex** file.
9. Click **Program Device**.
10. Check the log for the following output:
11. Unplug the power and SWD connections.
12. Plug in Cube, connect to Mission Planner and verify Here4 shows up in DroneCAN (in **MAINTENANCE** mode).
13. Update the Here4 (**Menu** -> **Update** -> **Yes, search the internet for updates**).
14. Verify Here4 shows up in **OPERATIONAL** mode.
## Connect Programming Devices
This section contains the pinout on either side to assist in connecting the J-Link or ST-Link device to the SWD port. The **same pinout is used for J-Link and ST-Link devices** with 20-pin connectors.
Solder or crimp the 6-pin JST SUR wires onto 2.54 mm female header plugs (if using programming devices with header pins).