[Core] Add CMSIS-RTOS2 threading backend

[GwnDaan]

Implements the threading intent of #319 and supersedes the approach in #458 on current main. The goal is to enable embedded RTOS platforms such as Zephyr and FreeRTOS without requiring standard-library threading support.

• Adds CMSIS-RTOS2 as an alternative backend in the existing isobus threading abstraction.
• Moves direct stack use of std::thread, mutexes, condition variables, sleep, and yield onto that abstraction where needed, including CAN, TC, and VT workers.
• Preserves normal std-threaded and CAN_STACK_DISABLE_THREADS behavior. No namespace std changes.
• Removes the old _gettimeofday requirement; current main provides TimeSource. Platform-specific CAN and time-source integration remain out of scope.

Draft: std and no-thread builds and existing tests pass, and the CMSIS code compiles against Arm and Zephyr CMSIS headers. Zephyr integration builds, hardware testing, and RTOS runtime testing are still pending.

[Copilot]

Copilot review overview

🟡 Changes recommended

The disabled-thread backend currently fails compilation and skips VT parsing, while TC worker reinitialization can terminate the process.

Review effort: Balanced
Findings: 2 · 1

Open (3)

• Reap retained worker before reinitializing the thread · New
• Add LockGuard fallback for disabled-thread and Arduino builds · New
• Run VT object-pool parsing synchronously without threading · New

What changed in this PR

Adds CMSIS-RTOS2 support to the shared threading abstraction and migrates core worker threads and synchronization primitives.

Changes:

• Implements CMSIS mutex, thread, condition-variable, sleep, and yield wrappers.
• Migrates CAN, VT, and TC workers to the abstraction.
• Adds CMake backend selection and configuration validation.

File	Description
CMakeLists.txt	Adds CMSIS backend selection.
utility/​CMakeLists.txt	Exposes the CMSIS definition.
utility/​include/​isobus/​utility/​thread_synchronization.hpp	Implements threading backends.
isobus/​CMakeLists.txt	Configures Isobus for CMSIS.
isobus/​src/​isobus_virtual_terminal_working_set_base.cpp	Migrates working-set locks.
isobus/​src/​isobus_virtual_terminal_server_managed_working_set.cpp	Migrates parser thread and locks.
isobus/​src/​isobus_virtual_terminal_client.cpp	Migrates the VT worker thread.
isobus/​src/​isobus_task_controller_server.cpp	Migrates server synchronization.
isobus/​src/​isobus_task_controller_client.cpp	Migrates the TC worker thread.
isobus/​include/​isobus/​isobus/​isobus_virtual_terminal_working_set_base.hpp	Uses abstract mutex type.
isobus/​include/​isobus/​isobus/​isobus_virtual_terminal_server_managed_working_set.hpp	Uses abstract thread type.
isobus/​include/​isobus/​isobus/​isobus_virtual_terminal_client.hpp	Uses owned abstract thread.
isobus/​include/​isobus/​isobus/​isobus_task_controller_server.hpp	Exposes abstract synchronization types.
isobus/​include/​isobus/​isobus/​isobus_task_controller_client.hpp	Uses owned abstract thread.
hardware_integration/​CMakeLists.txt	Configures hardware integration for CMSIS.
hardware_integration/​src/​can_hardware_interface.cpp	Migrates CAN worker synchronization.
hardware_integration/​include/​isobus/​hardware_integration/​can_hardware_interface.hpp	Declares abstract CAN threading members.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
56.4% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud