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Flash the Nano over WiFi through the ESP32
- ESP32: NanoFlashBridge on TCP port 2323. A connection power cycles the Nano into its bootloader and bridges TCP <-> Serial2 at 57600 baud; the clock pauses during the session, 10 s idle timeout - tools/nano_net_upload.py: STK500v1 uploader over TCP (standard library only), with sync retries, write and read-back verification. avrdude 6.3 net: ports are broken on Windows, so avrdude is not used - New nano_ota environment: pio run -e nano_ota -t upload - README: usage, requirements, troubleshooting; TODO for hardware test Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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@@ -40,6 +40,7 @@ src/esp32/ ESP32 firmware
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secrets.example.h template for WiFi / MQTT credentials
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test/test_nano/ unit tests for the Nano firmware (run on the PC)
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test/mocks/ fake Arduino, EEPROM and display driver for the tests
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tools/nano_net_upload.py uploader for flashing the Nano over WiFi
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archive/ old, unused sketches kept for reference
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CLAUDE.md project notes for Claude Code
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```
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@@ -57,12 +58,14 @@ this folder.
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| Environment | Board | Upload method |
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|-------------|-------|---------------|
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| `nano` | Arduino Nano (ATmega328P) | USB (`COM10`) |
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| `nano_ota` | Arduino Nano (ATmega328P) | Over WiFi through the ESP32 (`10.1.1.198`). See [Flashing the Nano over WiFi](#flashing-the-nano-over-wifi). |
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| `esp32` | ESP32 DevKit v1 | OTA over WiFi (`10.1.1.198`) |
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| `esp32_usb` | ESP32 DevKit v1 | USB (`COM11`). Use it for the first flash or for recovery. |
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```sh
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pio run # build nano + esp32
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pio run -e nano -t upload # flash the Nano
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pio run -e nano -t upload # flash the Nano over USB
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pio run -e nano_ota -t upload # flash the Nano over WiFi, through the ESP32
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pio run -e esp32 -t upload # flash the ESP32 over the air
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pio run -e esp32_usb -t upload # flash the ESP32 over USB
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pio device monitor -e nano # serial monitor
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@@ -76,7 +79,60 @@ In VS Code you can also pick the environment in the PlatformIO status bar.
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> **Tip:** The ESP32 → Nano wire goes to the Nano's RX pin, which the Nano's USB chip
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> also uses. Disconnect that wire before you flash the Nano over USB, or the upload may
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> fail.
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> fail. Flashing over WiFi (`nano_ota`) doesn't have this problem.
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## Flashing the Nano over WiFi
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The ESP32 can flash the Nano for you, so you don't need a USB cable at the display:
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```sh
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pio run -e nano_ota -t upload
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```
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What happens:
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1. The uploader ([tools/nano_net_upload.py](tools/nano_net_upload.py)) connects to the
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ESP32 on TCP port **2323**.
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2. The ESP32 pauses the clock and switches the relay off for 1 second, then on again. This
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restarts the Nano, and its bootloader starts.
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3. The ESP32 switches its link to the bootloader's 57600 baud and passes bytes between
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WiFi and the Nano.
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4. The uploader writes the new firmware and reads it back to verify it.
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5. When the uploader disconnects, the ESP32 switches the relay off. The clock powers the
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Nano on again with the new firmware and continues.
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The display goes dark for the duration of the upload, which takes a few seconds.
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**Requirements**
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- The reply wire must be connected: Nano D1 (TX) → voltage divider → ESP32 GPIO 16. The
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uploader needs the bootloader's answers.
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- The ESP32 must be running firmware with the flash bridge (this version or newer).
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- The Nano must have the **old bootloader** (the `nanoatmega328` board, 57600 baud), which
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also runs at power-on. The newer Optiboot bootloader only runs after a reset-pin reset,
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so the relay power cycle would not start it.
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**Settings**
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- ESP32 IP address: `upload_port` in the `nano_ota` environment in `platformio.ini`. You
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can add a port number: `10.1.1.198:2323`. For a one-time different address, use
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`pio run -e nano_ota -t upload --upload-port 10.1.1.50`.
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- Port, baud rate and power-off time: `NANO_FLASH_PORT`, `NANO_BOOTLOADER_BAUD` and
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`NANO_POWER_OFF_TIME` in `src/esp32/libs.h`.
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**If it fails**
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| Message | Cause |
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|---------|-------|
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| `can't connect to ...` | Wrong IP address, or the ESP32 is offline or running older firmware |
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| `no answer from the Nano bootloader` | Reply wire missing, or the Nano has Optiboot |
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| `bad reply to command ...` / `verify failed` | Connection problem. Try again. A failed upload can leave the Nano without working firmware, but the bootloader itself is never overwritten, so flashing again (over WiFi or USB) always fixes it. |
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The ESP32 ends the session after 10 seconds without data, so the clock always resumes,
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even if the uploader is interrupted.
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> **Security:** anyone on your network can connect to port 2323 and flash the Nano, just
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> like the ESP32's own OTA has no password. Keep the display on a trusted network.
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## Wiring between ESP32 and Nano
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@@ -86,7 +142,7 @@ The ESP32 talks to the Nano on **UART2** (`Serial2`, 115200 baud). The ESP32's o
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| ESP32 | Nano | Notes |
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|-------|------|-------|
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| GPIO 17 (TX2) | D0 (RX) | Display commands |
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| GPIO 16 (RX2) | D1 (TX) | `READY` and `ERR` replies. Use a 5 V → 3.3 V voltage divider (e.g. 1 kΩ / 2 kΩ), because the ESP32 is not 5 V tolerant. Optional: without it, the ESP waits a fixed 3 s after power-on. |
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| GPIO 16 (RX2) | D1 (TX) | `READY` and `ERR` replies, and bootloader answers when flashing over WiFi. Use a 5 V → 3.3 V voltage divider (e.g. 1 kΩ / 2 kΩ), because the ESP32 is not 5 V tolerant. Without it, the ESP waits a fixed 3 s after power-on, and `nano_ota` doesn't work. |
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| GND | GND | Common ground |
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| GPIO 13 | Relay input | Relay powers the panels and the Nano (`LOW` = on) |
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@@ -118,7 +174,11 @@ The serial protocol is described in [src/nano/README.md](src/nano/README.md).
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you flash this firmware, or the display gets no data. See
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[Wiring between ESP32 and Nano](#wiring-between-esp32-and-nano).
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- [ ] **Add the reply wire:** Nano D1 (TX) → voltage divider → ESP32 GPIO 16 (RX2). With it,
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the ESP sends the first frame as soon as the Nano is ready, instead of after 3 s.
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the ESP sends the first frame as soon as the Nano is ready, instead of after 3 s, and
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the Nano can be flashed over WiFi (`nano_ota`).
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- [ ] **Test flashing over WiFi on the real hardware.** The uploader is tested against a
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simulated bootloader, not yet against the real Nano. Check especially that the old
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bootloader starts after the relay power cycle.
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- [ ] **Check the boot timing.** Build the Nano with `MEASURE_REFRESH` to see how long a
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full redraw takes. If the reply wire isn't fitted, check that 3 s
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(`NANO_BOOT_TIMEOUT`) is enough for the Nano to boot.
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