260827-DHA_BT_Telecoil_PD5

Self-contained STM32CubeIDE project for the Bluetooth and telecoil application contribution, targeting the NUCLEO-F446RE / STM32F446RE.

The assessed Application/ layer is hardware-independent. It contains no STM32 HAL calls, device-register access or dynamic allocation. The small Board/ layer is used only to run the portable application and tests on the F446.

Quick start

1. In STM32CubeIDE select File -> Import -> General -> Projects from Folder or Archive.
2. Choose the submission ZIP and import 260827-DHA_BT_Telecoil_PD5.
3. Do not regenerate code from the .ioc; the supplied project already contains the custom build configurations.
4. Build and run the three configurations:

Configuration	Purpose	Successful result
Debug	Deterministic application demonstration	Completes with deadline_misses=0; LD2 on
Testing	Primary automated unit-test suite	256 Tests 0 Failures 0 Ignored / OK; LD2 on
SelfTest	Supplementary independent regression checks	52 checks, 0 failures, OK; LD2 on

USART2/ST-LINK VCP output is 115200 baud, 8-N-1. Exact verification and GitHub steps are in VERIFICATION.md.

Application modules

Module	Responsibility
connectivity_controller	M1-M4 state machine, Bluetooth > telecoil priority, fault/reconnect/recovery/idle timing
connectivity_service	Top-level orchestration, source processing, diagnostics and timing contract
connectivity_actions	Injected connect/reconnect/low-power callbacks for mocks or later integration
control_protocol	Bounded mode/source command parser
bt_profile	BT401 configuration sequence through injected send/delay callbacks
audio_processing	PCM conversion, Q15 gain, stereo-to-mono and mute
pcm_transport	Portable packed/interleaved PCM framing helpers
audio_dynamics	DC rejection, bounded AGC smoothing and peak limiting
telecoil_detector	RMS/mean-absolute/peak-to-peak/clipping metrics with hysteresis
telecoil_filter	Stateful two-biquad conditioning at 16 kHz and 48 kHz
signal_quality	Integer/fixed-point 20 dB RMS signal-to-noise classification

Verification

The project provides:

• 256 automated unit tests;
• 52 supplementary framework-independent checks;
• a 100,000-step deterministic state-machine stress test;
• GCC and Clang host builds;
• AddressSanitizer and UndefinedBehaviourSanitizer;
• GCC static analysis;
• executable-line coverage with a 98% minimum gate;
• mutation testing of the Bluetooth-priority rule;
• CMake/CTest host execution;
• GitHub Actions with GCC, Clang and GNU Arm Cortex-M4 jobs.

The latest measured application line coverage is 99.22% (888/895 executable lines).

Run the complete host verification with:

make -f Makefile.host verify

or CMake/CTest with:

cmake --preset host-debug
cmake --build --preset host-debug
ctest --preset host-debug

Requirements boundary

REQUIREMENTS_TRACEABILITY.md maps requirements 1.1-1.20 to the portable implementation and automated evidence. Physical I2S timing, true Bluetooth-to-output latency, measured telecoil SNR and idle power remain system-integration measurements rather than software-only claims.

Design details are summarised in docs/ARCHITECTURE.md.

Project layout

Application/        Portable application logic
Board/              Minimal STM32F446RE execution adapters
Core/               Entry point, startup and bare-metal Newlib stubs
Tests/              Primary 256-test suite
IndependentTests/   Supplementary 52-check suite
Host/               Host runners and deterministic stress test
Scripts/            Coverage and mutation helpers
Matlab/             Supporting DSP validation
.github/workflows/  Continuous-integration workflow
docs/               Architecture notes

References

1. STMicroelectronics, RM0390 — STM32F446xx advanced Arm-based 32-bit MCUs Reference Manual. Used for the thin Board/ and startup-layer register definitions and peripheral configuration.

2. STMicroelectronics, UM1724 — STM32 Nucleo-64 boards (MB1136) User Manual. Used for NUCLEO-F446RE board pin mapping, LD2 and ST-LINK virtual COM-port context.

3. BT401 Bluetooth Audio Module User Manual, Version 1.6. Manufacturer documentation used for the serial framing and AT-command meanings represented by bt_profile.

4. ThrowTheSwitch, Unity — A Test Framework for C. The project follows the Unity-style C test API and assertion syntax; the compact files under Tests/Unity/ are a local course-aligned implementation rather than a copy of the current upstream Unity source distribution.

5. MathWorks, MATLAB R2025a. Used only for independent offline verification of the implemented DSP equations and frequency response; MATLAB is not a runtime dependency of the embedded application.

Acknowledgements

Selected high-level Bluetooth/audio-processing ideas were refactored from my earlier digital-hearing-aid prototype into hardware-independent modules for this submission. No STM32 HAL-dependent application logic was carried into the assessed Application/ layer.

Generative AI (OpenAI ChatGPT, GPT-5.6 Sol) was used during development for software-architecture discussion, C-code drafting and refactoring, unit-test generation, debugging of build/linker issues, host/CI verification setup, MATLAB verification-script drafting, and documentation review.

All generated or adapted material was manually reviewed and validated through clean STM32CubeIDE builds, execution on the NUCLEO-F446RE, automated unit tests, independent regression checks, host testing, sanitizers, static analysis, coverage, mutation testing and GitHub Actions. Final engineering decisions and responsibility for the submitted work remain with the author.