Flipdot-display/CLAUDE.md

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, nano_ota, esp32 (OTA to 10.1.1.198), esp32_usb (COM11), and the PC test environments test_nano and test_esp32. 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.
• nano_ota flashes the Nano over WiFi: tools/nano_net_upload.py (STK500v1 over TCP) talks to NanoFlashBridge on the ESP32 (port 2323). The uploader first sends FLASH <baud>\n. The ESP power cycles the Nano (plus an optional reset pulse on NANO_RESET_PIN), answers OK\n, then passes the bytes through at that baud rate. --baud=auto tries 57600 (old ATmegaBOOT, which also starts after a power cycle), then 115200 (Optiboot, which only starts after a reset-pin reset, so it needs NANO_RESET_PIN). avrdude 6.3's net: port is broken on Windows (ser_drain() fails), which is why the uploader is a Python script. The uploader only uses the Python standard library. Test it against a simulated bootloader before changing it.
• After any change, build both targets (pio run) and run the tests (pio test -e test_nano -e test_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 ESP32 talks to the Nano on Serial2 (owned by NanoLink, GPIO 17 TX / GPIO 16 RX). Serial (UART0/USB) is free for debug output. Never write debug text to Serial2: the Nano runs lines that start with s/S/F/D/P/B/R/T/G/N/E as commands.
• Open hardware TODOs are listed in the README TODO section. Update it when one is done.
• src/esp32/secrets.h holds the real credentials and is gitignored. Never commit it. Add new secrets to secrets.example.h as placeholders.
• The relay (ESP32 GPIO 13, LOW = on) powers both the panels and the Nano. Each time it switches on, the Nano cold-boots and then sends READY. NanoLink::on() waits for that message, at most NANO_BOOT_TIMEOUT. The timeout also covers the case where the Nano's TX isn't wired to the ESP's RX.
• NanoLink::off() ends Serial2 and sets its TX pin to input. Otherwise the idle-high TX line powers the Nano through its RX pin. Never send display commands while NanoLink::isOn() is false (DisplayController takes care of this).
• The Nano keeps no state over a power cycle except the flip time in EEPROM. The driver forces a full redraw on the first display() after boot (_force_next).
• Hardware is not available here. Builds can be checked, but runtime behaviour can't.

Nano serial parser (src/nano/main.cpp)

• Files: main.cpp (setup/loop, refresh), config.h (all constants and debug defines), command_parser.* (protocol, one method per command), settings.* (EEPROM).
• Line based and non-blocking: bytes are collected into a 64-character buffer and a command runs when \n arrives. Bitmap (B) pixel data is the exception. It is drawn while it arrives, so it can be longer than the buffer. Keep loop() free of busy-waits.
• A full redraw (display(true)) blocks for about 0.5 s, which overflows the 64-byte serial receive buffer. Only run it when no data is expected: right after a D, or after 2 s with no serial data. The ESP only sends a frame (ending with D) when the screen changes, mostly once a minute.
• Flip time is stored in EEPROM as a magic word at address 0 and a uint16_t at address 2. Values outside 50–2000 µs are rejected.
• The Nano only replies READY (at boot) and ERR: .... There is no per-frame acknowledgement. Whether the Nano's TX is wired to the ESP's RX is unconfirmed, so every wait for a reply needs a timeout.
• Unit tests: pio test -e test_nano runs test/test_nano/ on the PC with the fakes in test/mocks/ (Arduino, EEPROM, and a BROSE9323 that records calls). It needs gcc on PATH (Strawberry Perl provides it at C:\Strawberry\c\bin). Add a test for every protocol change. The mocks only implement what the Nano code uses, so extend them when new Arduino or driver functions are called.
• The board environments have test_ignore = *, so test firmware is never uploaded. Plain pio test runs nothing; always pass -e test_nano -e test_esp32.

ESP32 structure (src/esp32/)

• Folders: logic/ (pure C++, no Arduino includes, tested in test/test_esp32), display/ (frames and bitmaps), nano_link/ (relay, serial, flash bridge), net/ (WiFi/OTA, Home Assistant). Includes are relative to src/esp32 (-I src/esp32), e.g. #include "logic/schedule.h".
• DisplayController holds the display logic and only uses the DisplayPower and Frames interfaces. Put new behaviour there, behind those interfaces, so it stays testable. logic/ must not include Arduino headers, or test_esp32 stops building.
• All settings are in config.h. Keep it free of Arduino types for the same reason.
• Frames are only sent when the screen changes. The schedule uses 08:00 as the start of the day on purpose (that is what the old code did, and the README documents it).
• Home Assistant switches are not optimistic: callbacks must call sender->setState(). The unique ids (FlipDotDisplayPower, FlipDotDisplayMode, FlipDotDisplayOffImage, FlipDotDisplayStopwatch, ...) and HA_DEVICE_ID must stay the same, or Home Assistant creates new entities.

Keeping ESP32 OTA alive (most important requirement)

• The user never wants to need USB for the ESP32 again. Any change must keep OTA working, also when the new code crashes or hangs.
• system/firmware_guard.cpp overrides the Arduino core's weak verifyRollbackLater() (C linkage) to return true. A new OTA image stays PENDING_VERIFY until it has run FIRMWARE_VALID_TIME with WiFi. Any restart before that makes the bootloader roll back. Check with nm that the strong symbol is linked after toolchain or core updates.
• The task watchdog (WATCHDOG_TIMEOUT_S) covers loop(). ArduinoOTA's onStart stops it, because an upload blocks loop(). Never block loop() for 30 s or longer.
• The crash counter lives in RTC_NOINIT_ATTR memory. Decisions are in logic/boot_policy.* (tested). Safe mode runs only WiFi + OTA.
• Keep otaLoop() and firmwareGuardLoop() at the top of loop(), before anything that can return early or block. Keep firmwareGuardBegin() first in setup(): it holds the power-cycle trigger for the recovery app.
• Flash layout partitions.csv: factory = recovery app (src/recovery, env recovery, USB only), ota_0/ota_1 = clock firmware. esp32_usb uploads to 0x110000 (board_upload.offset_address) so it never overwrites the recovery app. Check with pio run -e <env> -t envdump (ESP32_APP_OFFSET) after changing upload settings.
• The recovery app compiles esp32/logic/boot_policy.cpp, esp32/system/system_store.cpp, esp32/system/boot_target.cpp, esp32/nano_link/nano_link.cpp, esp32/display/status_screen.cpp and esp32/display/text.cpp (see its build_src_filter). Keep those free of clock-firmware dependencies.
• Status messages (StatusScreen) are at most 14 characters per line, 2 lines. The recovery app powers the display off after each message (flipdots keep the image). Both apps share NVS namespace flipdot. RTC memory is not shared between the apps (different layouts).
• rebootToRecovery() selects the factory partition, which erases otadata. The recovery app later selects the clock slot again (startMainFirmware()), so the clock firmware is PENDING_VERIFY again and must pass the 60 s check, or the bootloader falls back to the recovery app.
• The clock firmware still works on the old flash layout (no factory partition): rebootToRecovery() returns, and the callers fall back to OTA-only mode or a restart.
• Arduino's esp_app_desc_t version and date come from the precompiled core, so the clock firmware stores FIRMWARE_VERSION per slot in NVS for the recovery page.

ESP32 web UI

• app.cpp owns the objects and the actions (settings, page, live mode, restart); web/web_ui.cpp is the JSON API (endpoints listed in web_ui.h), web/web_page.h the single HTML/JS page (raw string literal in PROGMEM). Keep image work in the browser; the ESP32 only handles 418-character hex bitmaps (logic/bitmap_format.h, MSB = left dot).
• Settings: logic/settings.h struct with defaults = original behaviour, stored as an NVS blob with a version (system/settings_store.cpp). When the struct changes, bump VERSION there (old records then fall back to defaults).
• Bitmaps on LittleFS in the spiffs partition (/bitmaps/<name>.bin, 209 bytes). Names are restricted (validBitmapName), which also makes them safe in paths and JSON.
• The display mirror comes from the driver's shadow buffer (BROSE9323::shownPixel).
• Dynamic pages (logic/page.h): background per time slot + elements, stored as a versioned binary struct (display/page_store.cpp, bump VERSION when DynamicPage changes). They are drawn only on the ESP32 (logic/page_render), also for the web previews, so there is one renderer. Pages and bitmaps share one namespace (checked in app.cpp); things a page uses can't be deleted. The built-in page "Clock" replaces the old hardcoded clock (also the default and the HA "Clock" option).
• Moving pages: renderPage() returns when the page changes next (scroll step, second); FlipdotFrames sends those frames as D1 (no effect) and paces them by the estimated flip time, because the Nano has no acknowledgement. Character 127 is the degree sign in page texts and fonts (UTF-8 ° in JSON).
• Fonts use the "FDF1" format of logic/font.h; the web page writes the same format. logic/builtin_fonts.cpp is generated: change tools/make_builtin_fonts.py and rerun it.
• Home Assistant values come from HA's REST API (net/ha_api), one blocking request per loop() with HA_HTTP_TIMEOUT. Keep it that way (watchdog, OTA).
• Check the page's JavaScript after changes: extract the <script> part and run node --check on it (node is installed).

Git

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