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As of 2025-07-24

How to Write Firmware to ESP32

How to write firmware to the ESP32 mounted on TWELITE SPOT

1: How to Write Sketches to ESP32

2: How to Write Files to ESP32

3: How to Specify the Partition Table for Writing to ESP32

This guide explains how to write firmware to the ESP32 mounted on the TWELITE SPOT.

1 - How to Write Sketches to ESP32

How to write sketches to the ESP32 mounted on TWELITE SPOT

This guide explains how to write Arduino sketches to the ESP32 mounted on TWELITE SPOT.

Connecting to the Host

Connect TWELITE R3 / R2

Connect the TWELITE R3 / R2 to the 7P interface (the side labeled ESP32).

Connect Power

Supply 5V power to the USB-C connector on the side.

Always connect the TWELITE R3 / R2 to the TWELITE SPOT in the same orientation as shown above. Connecting it incorrectly may damage the TWELITE SPOT or the TWELITE R3 / R2.

Operating Arduino IDE

Open the Sketch

Launch the Arduino IDE and open the sketch you want to write.

Select the Serial Port

From the Tools -> Serial Port menu, select the port for the TWELITE R3 / R2.

On Windows, the serial port name will be like COM?, and on macOS/Linux, it will be like /dev/tty?.

Start ESP32 in Programming Mode

Press the ESP32 reset switch EN(RST) and the ESP32 boot switch BOOT on the TWELITE SPOT, then release them in the order of EN(RST) -> BOOT.

By pressing BOOT while resetting, you can enter the ESP32 programming mode.

Execute Writing

Click the Write to Microcontroller Board button in Arduino IDE.

When writing is complete, Hard resetting via RTS pin... will appear at the bottom of the screen.

If writing fails and the following message appears, try changing the USB port or USB cable you are using.

A serial exception error occurred: Could not configure port: (6, 'Device not configured')

Reset ESP32

After writing is complete, press and release the ESP32 reset switch EN(RST) on the TWELITE SPOT to reset the ESP32.

If you do not reset, you cannot exit programming mode.

2 - How to Write Files to ESP32

How to write files to the ESP32 mounted on TWELITE SPOT

This guide explains how to write files (the files under the data/ folder) to the ESP32 mounted on TWELITE SPOT.

This article introduces an advanced topic (how to treat the flash area of the ESP32 mounted on TWELITE SPOT as a file system and write files such as HTML).

For example, if you do not need to write HTML files to TWELITE SPOT to behave as a web server (implemented in the spot-server sample) or write encryption key files to TWELITE SPOT, you can ignore the contents of this article.

This article uses third-party open-source software.

We cannot provide detailed instructions on third-party software usage. Also, we assume no responsibility for any damages caused by using third-party software.

The method introduced in this article requires Arduino IDE 1.x. Due to technical constraints, as of May 2023, Arduino IDE 2.x is not supported.

Because the plugin used here is written in Java, it does not work with Arduino IDE 2.x, which is not Java-based unlike Arduino IDE 1.x. For more details, see the Arduino IDE GitHub issue (Missing support for external tools / plugins · Issue #58 · arduino/arduino-ide) (in English).

Installing the Plugin

Install the Arduino plugin (arduino-esp32fs-plugin) to write files to the ESP32 flash area.

Downloading the Plugin

Download esp32fs.zip from the following page:

Release Update to support Big Sur · lorol/arduino-esp32fs-plugin

The original arduino-esp32fs-plugin is me-no-dev/arduino-esp32fs-plugin, but here we use the forked version lorol/arduino-esp32fs-plugin which supports the latest LittleFS file system.

Installing the Plugin

Extract the downloaded esp32fs.zip.
If there is no tools folder in your Arduino sketchbook location (set in Arduino IDE preferences, e.g., C:\Users\foo\Documents\Arduino), create it.
Create the folder ESP32FS/tool inside the tools folder and place the esp32fs.jar file extracted from the zip there. (Example path: C:\Users\foo\Documents\Arduino\tools\ESP32FS\tool\esp32fs.jar).
The plugin will be available the next time you start Arduino IDE.

Connecting to the Host

Connect TWELITE R3 / R2

Connect TWELITE R3 / R2 to the 7P interface side labeled ESP32.

Connect Power

Supply 5V power to the USB-C connector on the side.

Always connect TWELITE R3 / R2 to TWELITE SPOT in the same orientation as shown above. Connecting in the wrong orientation may damage TWELITE SPOT or TWELITE R3 / R2.

Arduino IDE Operations

Open the Sketch

Start Arduino IDE and open the sketch.

Place Files to Write

Open Sketch -> Show Sketch Folder.
Create a data folder at the same level as the sketch file (.ino).
Place the files to write inside the data folder.

The directory structure inside the data folder is preserved in the flash area.

Select Serial Port

From the Tools -> Port menu, select the port for TWELITE R3 / R2.

On Windows, serial ports are named like COM?, and on macOS/Linux, like /dev/tty?.

Boot ESP32 in Programming Mode

Press the ESP32 reset switch EN(RST) and the ESP32 boot switch BOOT on TWELITE SPOT, then release them in the order EN(RST) -> BOOT.

Resetting while holding BOOT switches ESP32 into programming mode.

Execute Writing

Click Tools -> ESP32 Sketch Data Upload.
At Select FS for /data folder, select LittleFS.

Click OK.

When writing completes, Hard resetting via RTS pin... is displayed at the bottom of the screen.

Depending on your environment, writing may fail with a message like this (confirmed on macOS):

`Error: esptool not found!`

In that case, placing esptool.py in the Arduino15 folder/packages/esp32/tools/esptool_py/<version>/esptool.py might resolve the issue.

For example, on macOS, obtain esptool.py and create a symbolic link as follows:


/usr/bin/pip3 install esptool
ln -s ~/Library/Python/3.9/bin/esptool.py ~/Library/Arduino15/packages/esp32/tools/esptool_py/4.5.1/esptool.py

Note: Specify /usr/bin/pip3 to avoid installing in the Homebrew directory.

Reset ESP32

After writing completes, press and release the ESP32 reset switch EN(RST) on TWELITE SPOT to reset ESP32.

3 - How to Specify the Partition Table for Writing to ESP32

How to apply any partition table when writing to the ESP32 mounted on TWELITE SPOT

This guide explains how to apply any partition table when writing sketches or files to the ESP32 mounted on TWELITE SPOT.

This article introduces an advanced topic (how to specify the partition table of the flash area).

If you use the partition table settings included by default in the ESP32 Arduino Core (e.g., Default 4MB with spiffs), you can ignore this article.

We assume no responsibility for any damages caused by applying the settings described in this article.

Creating the Definition File

The partition table is defined in a csv file.

In the example below, out of the 16MB flash area, 8MB is allocated for the file system.

# TWELITE SPOT 16MB with 8MB LittleFS
# Name,  Type, SubType, Offset,   Size,     Flags
nvs,     data, nvs,     0x9000,   0x5000,
otadata, data, ota,     0xE000,   0x2000,
app0,    app,  ota_0,   0x10000,  0x7F0000,
spiffs,  data, spiffs,  0x800000, 0x800000,

TWELITE SPOT 16MB with 8MB LittleFS is the name displayed in the Arduino IDE.
nvs is the area used by the system. Do not change.
otadata is the area used when using OTA. Do not change.
app0 is the area where the firmware is written.
spiffs is the area used by the LittleFS file system.

The units of the Offset and Size columns in the csv file are bytes, expressed in hexadecimal.

Therefore, the usable sizes for firmware and file system in the above example can be calculated as follows:

Size of app0: 0x7F0000 = 8323072, approximately 7.875MB
Size of spiffs: 0x800000 = 8388608, exactly 8MB

Registering the Definition File

Open the Arduino15 folder and add the csv file to the following path:

Arduino15/packages/esp32/hardware/esp32/x.x.x/tools/partitions

x.x.x is the version of Arduino core for the ESP32

Applying the Partition Table

From the Arduino IDE toolbar, open Tools -> Partition Scheme and select the added partition table.

The selected partition table will be applied to subsequent firmware and file system writes.

If a file named partitions.csv is placed in the same location as the sketch file, that file takes precedence. However, the display in the Arduino IDE does not change, which may cause confusion.