C SDK

The C SDK is for gateways, embedded Linux, and device programs that call serial ports, GPIO, driver libraries, or C/C++ modules directly. The generated package handles MQTT connectivity, command responses, and data reporting; connect the real hardware logic in src/main.c.

Start with	Purpose
src/main.c	Implement command handling, hardware calls, and reports
CMakeLists.txt / README.md	Check dependencies, build options, and platform notes

For .env, runtime-model.json, and device-spec.json, follow the shared project file and model rules.

Projects for the current adapter

The examples below use an SDK project for devices managed directly by Device Agent. Other adapters may use different callbacks; follow the package README. Where writable state is supported, implement its update callback as well as command handling, and report actual values after applying them to hardware.

Build and Start

1. Download and extract the package, then open its root directory.
2. Check the generated .env. Copy .env.example only when it is absent, then complete connection settings.
3. Install dependencies and complete the first CMake build.
4. Connect the real hardware logic in src/main.c, then rebuild.
5. Start build/device and verify it in the Device Agent workspace.

The minimum build and start commands are:

test -f .env || cp .env.example .env
set -a && source .env && set +a
cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build
./build/device

The build requires pkg-config, and the MQTT client requires libmosquitto. CMake uses the system cJSON when available and fetches it otherwise. Voice requires libwebsockets and OpenSSL, while vision requires libcurl. Disable either module when it is not needed:

cmake -B build \
  -DCMAKE_BUILD_TYPE=Release \
  -DDA_BUILD_VOICE=OFF \
  -DDA_BUILD_VISION=OFF

The C program does not load .env itself. Export it into the current environment before startup, as shown above. The initial state is generated from valid defaults, enum values, and type constraints in the model. Replace these example values with real device state during integration.

Implement Commands, State, and Events

The example project's handle_command() validates commands and parameters before handling vision or device actions and correlating responses and reports. Add hardware calls after validation and replace simulated mappings with actual values. Return an error on hardware failure instead of reporting success. Preserve the handler's validation and response correlation when adding hardware logic.

The three report types serve different purposes:

Type	Use it for	C API
Status	Online state or a changed state snapshot	da_client_send_status()
Telemetry	Current values such as temperature or power	da_client_send_telemetry()
Event	Discrete occurrences such as alerts or button presses	da_client_send_event()

Call these interfaces after the client connects. This example uses the current_temperature property and over_temperature event from Define a Device Agent:

da_client_send_status(client, "online", "{\"current_temperature\":26.5}");
da_client_send_telemetry(client, "state", "{\"current_temperature\":22.5}");
da_client_send_event(client, "over_temperature", "alert", "{\"current_temperature\":32.5}");

Add Voice and Vision

Voice

include/device_agent/voice_client.h and src/voice_client.c provide the device-side voice client. examples/voice_chat.c includes the URL selected when the package was generated. Export VOICE_WS_URL before startup only when you need to override it. Connect microphone capture, speaker playback, and callbacks to the client for a real device:

da_voice_options_t opts = {
    .ws_url = "ws://<gateway>:3001/ws/voice",
    .device_id = "device-001",
    .product_id = "agent-001",
};

da_voice_client_t *voice = da_voice_client_new(&opts, &callbacks);
da_voice_client_connect(voice);
da_voice_client_start_listening(voice, "manual");
da_voice_client_send_audio(voice, pcm_samples, sample_count);
da_voice_client_stop_listening(voice);

Vision

include/device_agent/vision_client.h and src/vision_client.c provide the generated package's preset single-photo recognition flow; see the package README for its trigger commands. Implement camera, screenshot, or image-file input in capture_local_vision_image() in src/main.c, and set the service host with VOICE_CHAT_HOST. The generated code returns the recognition result as the command response.

See Voice Interaction and Camera and Vision for complete media settings. After startup, use the checks in SDK Access to verify online state, commands, state reports, and events.