> For the complete documentation index, see [llms.txt](https://docs.arkelectron.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.arkelectron.com/products/electronic-speed-controller/ark-4in1-esc/firmware/flash-bootloader.md).

# Flash Bootloader

## Flashing Bootloader via AM32

You can update the bootloader using the [AM32 Configurator](https://am32.ca/configurator). Once connected select "Flash firmware" and select the "Bootloader" tab. Download the **AM32-bootloader-updaters-amj.zip** from the [AM32-bootloader release artifacts](https://github.com/am32-firmware/AM32-bootloader/releases). Select the **AM32\_F051\_BL\_UPDATER\_PB4\_V15.amj.**

***

## Flashing Bootloader via SWD

If you're flashing an ESC without firmware or the firmware has become corrupted, you can reflash the ESC with SWD to bring it back to a fresh state.

For detailed instructions on ST-LINK setup, software installation, and usage, see the [ST-LINK Flashing Guide](/knowledge-base/knowledge-base/st-link-flashing-guide.md).

#### What You'll Need

* ARK 4IN1 ESC
* ST-LINK V3 Mini (recommended) or ST-LINK V2
* Computer running Windows or Ubuntu
* [AM32 bootloader file](/products/electronic-speed-controller/ark-4in1-esc/firmware.md#am32-bootloader-firmware)

#### Hardware Setup

The ARK 4IN1 ESC has 4 separate STM32F051 microcontrollers (one per motor channel), each with their own SWD interface on a single 10-pin debug connector. See the [pinout](/products/electronic-speed-controller/ark-4in1-esc/pinout.md) for the full connector diagram.

| Pin | Signal          |
| --- | --------------- |
| 1   | 3.3V            |
| 2   | SWDIO 1 (ESC 1) |
| 3   | SWCLK 1 (ESC 1) |
| 4   | SWDIO 2 (ESC 2) |
| 5   | SWCLK 2 (ESC 2) |
| 6   | SWDIO 3 (ESC 3) |
| 7   | SWCLK 3 (ESC 3) |
| 8   | SWDIO 4 (ESC 4) |
| 9   | SWCLK 4 (ESC 4) |
| 10  | GND             |

To flash each ESC, connect your ST-LINK to the corresponding SWDIO/SWCLK pair. For example, to flash ESC 1:

| ST-LINK Pin     | Debug Connector Pin | Signal  |
| --------------- | ------------------- | ------- |
| SWDIO           | Pin 2               | SWDIO 1 |
| SWCLK           | Pin 3               | SWCLK 1 |
| GND             | Pin 10              | GND     |
| 3.3V (optional) | Pin 1               | 3.3V    |

{% hint style="warning" %}
If your ESC is powered from a battery or power supply, **do not** connect the 3.3V line from the ST-LINK.
{% endhint %}

Repeat the process for ESC 2-4 using their respective SWDIO/SWCLK pins (4/5, 6/7, 8/9).

#### Flash the Bootloader

Flash each ESC MCU with the bootloader binary:

```bash
st-flash write AM32_F051_BOOTLOADER_PB4.bin 0x08000000
```


---

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