This lab shows how to implement real remote firmware updates from a browser for an ESP32-C6 board using PlatformIO + pioarduino and an Async Web OTA page powered by ElegantOTA.

You will:

• flash a first “baseline” firmware over USB,
• host an authenticated OTA webpage on the device,
• upload a new firmware from your browser,
• verify success with a visible NeoPixel behavior change,
• document basic threat-model thinking.

After completing this lab, you can:

1. Explain why OTA requires an A/B (dual-slot) style partition table.
2. Configure PlatformIO to use pioarduino and an OTA partition scheme.
3. Implement a device-hosted OTA updater available at /update.
4. Validate OTA end-to-end by changing device behavior without USB access.
5. Identify key security risks for OTA and apply simple mitigations.

What you are building:

• Your device runs a small web server.
• Visiting a web page opens a firmware upload page.
• The new firmware is written into the inactive OTA slot.
• After reboot, the bootloader selects the new slot.

Why two slots?

If an update fails mid-way (power loss, bad binary), the device still has a valid previous firmware to boot. This is the core reliability concept behind OTA on constrained devices.

Create a new PlatformIO project and create or replace your platformio.ini with:

platformio.ini

[env:sparrow_c6]
platform = https://github.com/pioarduino/platform-espressif32/releases/download/stable/platform-espressif32.zip
board = esp32-c6-devkitm-1
framework = arduino
monitor_speed = 115200
 
; Use OTA-capable partition table
board_build.partitions = sparrow_ota_4mb.csv
 
; Optional but often helpful
build_flags =
  -D CORE_DEBUG_LEVEL=1
  -D ARDUINO_USB_MODE=1
  -D ARDUINO_USB_CDC_ON_BOOT=1
  -D ESP32_C6_env
  -D ELEGANTOTA_USE_ASYNC_WEBSERVER=1
 
lib_deps =
  ESP32Async/AsyncTCP@^3.4.9
  ESP32Async/ESPAsyncWebServer@^3.9.2
  ayushsharma82/ElegantOTA
  adafruit/Adafruit NeoPixel
 
 
lib_ignore =
  AsyncTCP_RP2040W

In your project root, next to platformio.ini, create sparrow_ota_4mb.csv.

Paste this:

# Name,   Type, SubType, Offset,  Size,     Flags
nvs,      data, nvs,     0x9000,  0x5000,
otadata,  data, ota,     0xE000,  0x2000,
app0,     app,  ota_0,   0x10000, 0x140000,
app1,     app,  ota_1,   ,        0x140000,
spiffs,   data, spiffs,  ,        0xD0000,

This layout assumes 4MB internal flash and gives you two OTA application slots plus a small SPIFFS area.

Create ``src/main.cpp`` and paste the code from here then build and upload via USB.

You should see:

• Wi-Fi connection dots
• A printed IP address
• A message telling you to open ``/update``

In your browser:

• ``http:<device-ip>/`` * ``http:<device-ip>/update``

Log in with:

• user: ``admin``
• pass: ``change-me``

Now you will make a visible change and deliver it without USB. Add a small LED pattern into main.cpp, you can get the new code from here.