EWP apps are C++ components compiled into the firmware image. The firmware starts one app at a time through ApplicationManager; it does not load native app binaries at runtime.

App structure

Keep app-specific behavior in src/apps/. Existing apps commonly split their screen logic into a small module and adapt it to ersa::app::Application in src/apps/apps_registry.cpp.

Implement the application contract from include/ersa/app/application.h:

getId() returns a stable unique ID used by navigation.
getTitle() returns the display name.
render() draws through the hal::IDisplay interface.
onEvent() handles button and system events.
onEnter() and onExit() acquire and release app-scoped state.
tick() is for short, non-blocking work; do not wait on network or BLE I/O from the UI loop.
getPartialBounds() declares the area to refresh for app updates.

Apps should use framework services and HAL contracts. Do not include Arduino, ESP-IDF, or concrete peripheral-driver headers in app code. For network work, use the existing service flow and return promptly so input, BLE events, and clock updates continue to run.

Registering an app

Add the app module under src/apps/, with a header and implementation when the app has reusable screen logic.
Include its header in src/apps/apps_registry.cpp.
Add an Application adapter class there. Give it a unique ID and title, forward rendering and input to the app module, and handle lifecycle or periodic updates as needed.
Create a static app instance beside the other registered app instances.
Add manager.registerApp(&myApp); in registerAllApps() in that same file. The UI calls registerAllApps() during startup.
To make the app visible in the drawer, add a drawer item in src/apps/app_drawer.h and src/apps/app_drawer.cpp, then handle that item in the DrawerApp event switch in src/apps/apps_registry.cpp.
Build and run the checks below. Confirm drawer navigation, back navigation, button behavior, rendering bounds, and wake/sleep behavior on the watch.

src/CMakeLists.txt discovers project .cpp and .c files recursively, so a new source file under src/ is included in the firmware build automatically. App registration is still explicit; adding a source file alone does not make an app navigable.

Build and check

From the repository root:

make test       # host-side platform and service tests
make firmware   # default ESP32-C3 firmware build
./scripts/pio.sh run -e ErsaWearableC6  # ESP32-C6 firmware build
make docs       # wiki and generated C++ API reference

The firmware outputs are .pio/build/ErsaWearable/firmware.bin for C3 and .pio/build/ErsaWearableC6/firmware.bin for C6. Release assets include the platform in each filename. PlatformIO uses the project environment in platformio.ini and downloads its framework and libraries when needed.

App store and installable apps

There is no app store or runtime app installer today. App code is linked into the firmware, and updates replace one of the two OTA firmware slots. The current image already uses about 95% of one slot, and the partition table has no app-data filesystem. There is no dynamic linker or stable binary ABI for third-party native apps.

A hosted app catalog could list firmware releases, source projects, or compatible app bundles for developers to build themselves. Installing native apps independently would require a different runtime or operating system, storage reserved for app packages, a stable application ABI, and a security model. Those are substantial platform changes; the current flash layout does not have room for a conventional app store.

SDK and C++ reference

The generated C++ API reference documents project headers and implementation, including HALs, services, app contracts, and board support. It is built from the same source headers the app compiler uses; Doxygen comments on declarations provide the function reference.

PlatformIO pins the current firmware to ESP-IDF 4.4.7 and Arduino-ESP32 2.0.17. Use the upstream ESP-IDF 4.4 API reference and Arduino-ESP32 documentation for those vendor APIs. Their SDK headers and implementations are downloaded into PlatformIO's package cache; this project's Doxygen site documents Ersa code and links to the matching vendor references instead of duplicating SDK documentation.