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Harry Broeders edited this page Sep 23, 2022 · 4 revisions

Using pthreads in STM32CubeIDE

The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX threads (pthreads) are a standard for creating threads in C. STM32CubeIDE comes with a built-in support for FreeRTOS. However, it does not support pthreads out of the box. There is a standard POSIX API available for FreeRTOS which can be used to define tasks and inter task communication. The source code for the POSIX API is available on GitHub and can be included in a STM32CubeIDE project.

Example projects for pthreads in STM32CubeIDE

A number of example projects are provided in the zip-file pthreads.zip these projects are mend for the STM32F411E-DISCO development board, but can easily be ported to other STM32 boards.

Import this project into STM32CubeIDE with the menu-option File>Import..., General>Projects from Folder or Archive, Next, Archive, select the file pthread.zip, Open and Finish.

This zip file contains the following projects:

  • pthread: This program shows how two threads can run concurrent.
  • pthread_join: This program shows how to wait for a thread to finish.
  • pthread_par: This program shows how to pass parameters to a thread.
  • pthread_shared: This program shows a synchronization problem which occurs when two alternating threads share a variable.
  • mutex: This program shows how two threads can run concurrent and share a resource without a synchronization problem, by using a mutex.
  • mutex_priority_inheritance: This program shows that FreeRTOS uses priority inheritance.
  • pthread_philosophers: This program shows a classic deadlock problem, the dining philosophers, that can arise if threads lock two mutexes in the same order.
  • pthread_philosophers_solution: This program shows how to solve the dining philosophers problem by locking the mutexes in a different order.
  • pthread_philosophers_semaphore: This program shows how to solve the dining philosophers problem by allowing no more than four philosophers to eat at the same time. This is done by using a semaphore.
  • mqueue: This program shows how to use a message queue to communicate between threads.
  • mqueue_array: This program shows how to use a message queue to transfer an array of integers from one thread to another.
  • mqueue_struct: This program shows how to use a message queue to transfer a structure from one thread to another.
  • mqueue_prio: This program shows that the implementation of mqueue in FreeRTOS doesn't support priority. The msg_prio argument is iggnored, see https://docs.aws.amazon.com/freertos/latest/lib-ref/html2/posix/mqueue_8h.html#a753177f77f6eec2a80b57e8a68b36bed.

Copying and modifying the example projects

To copy a project, right-click on the project name in the Project Explorer, e.g. pthread, and select Copy. Press Ctrl+V and choose an appropriate name, e.g. pthread_copy. Remove the Debug folder from the pthread_copy project, rename pthread.cfg to pthread_copy.cfg, and rename pthread.launch to pthread_copy.launch. Open pthread_copy.launch and replace all occurrences of pthread by pthread_copy. Build and debug the project pthread_copy to verify that it is a correct copy of project pthread.

Adding the POSIX API to a STM32CubeIDE project

When you start with a new STM32CubeIDE FreeRTOS project, you have to add the POSIX API to the project. This can be copied from GitHub or from an example project. In the example projects the POSIX API is located in the folder Middlewares/Third_Party/Lab-Project-FreeRTOS-POSIX-master.

The STM32F411E-DISCO development board doesn't have support for printf and scanf which are used in the example projects. To enable printf and scanf semihosting is used, see https://www.st.com/resource/en/application_note/dm00354244-stm32-microcontroller-debug-toolbox-stmicroelectronics.pdf. The project must be debugged by using openOCD. More information can be found at http://fastbitlab.com/freertos-lecture-32-understanding-arm-semi-hosting-feature/.

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