# Flipdot display: notes for Claude

A PlatformIO project with two firmware targets for an 84×19 Brose flipdot clock.
See README.md for the overview.

## Layout and build

- `platformio.ini` has the environments `nano`, `esp32` (OTA to 10.1.1.198) and
  `esp32_usb` (COM11). The sources are split with `build_src_filter` (`src/nano/`,
  `src/esp32/`).
- `lib/BROSE9323/` is the shared driver. Its behaviour depends on build flags set in
  `platformio.ini`, not in the header:
  - `ESPSERIAL` (ESP32): draw calls become serial commands.
  - `FLIPDOT_PLCC_ADAPTER` (Nano, optional): alternative pinout.
- PlatformIO CLI is not on PATH. Run `~/.platformio/penv/Scripts/pio.exe run` (Git Bash)
  or `$env:USERPROFILE\.platformio\penv\Scripts\pio.exe run` (PowerShell).
- If an ESP32 build fails with `No module named 'intelhex'`, run
  `~/.platformio/penv/Scripts/python.exe -m pip install intelhex`.
- After any change, build both targets: `pio run -e nano -e esp32`.

## Constraints

- **Nano RAM is tight** (ATmega328P, 2 KB). The frame buffers are allocated with
  `calloc`. Avoid `String`, large stack buffers and new globals in Nano code. Put constant
  data in `PROGMEM`.
- The Nano and the ESP32 share one UART. On the ESP32, `Serial` is the display link, so
  **don't print debug output on the ESP32's `Serial`**: the Nano would read it as
  commands. The Nano ignores unknown command bytes, but text that starts with
  s/S/F/D/P/B/R/T will be run as a command.
- `src/esp32/secrets.h` holds the real credentials and is gitignored. Never commit it.
  Add new secrets to `secrets.example.h` as placeholders.
- Hardware is not available here. Builds can be checked, but runtime behaviour can't.

## Known quirks in the serial protocol (Nano `src/nano/main.cpp`)

- `T` waits for more than 6 bytes before parsing, but `T225\n` has only 4 after the `T`.
  It completes only when the next command arrives.
- The `T` value is stored with `EEPROM.update` in one byte, so values above 255 µs are
  truncated after a reboot.
- `P` (print text) busy-waits for a `\n` and has no timeout.

## Git

- Remote: https://mangavalk.com/mangavalk/Flipdot-display.git, branch `main`.