PranabNandy / FreeRTOS

FreeRTOS On STM32F4xx With Debugging

FreeRTOS APIs

Some Background

• Real-time deals with guarantees, not with raw speed. (Soft realtime and Hard Realtime)
• In Real-Time Computing timeliness is more important than performance.
• Time Deterministic – Response time to events is always almost constant.
• To deal with Priority Inversion problem, either it reschedules the tasks or change the LP Task to HP. Priority inversion avoidance
• Priority based preemptive scheduling mechanism
• No or very short Critical sections which disables the preemption

1. Introduce

• FreeRTOS is a real-time operating system kernel for embedded devices that has been ported to 35 MCU platforms
• It is designed to be small and simple. To make the code readable, easy to port, and maintainable, it is written mostly in C, but there are a few assembly functions included where needed (mostly in architecture-specific scheduler routines).
• It provides methods for multiple threads. A tick-less mode is provided for low power applications.
• FreeRTOS kernel features:
  • Pre-emptive or co-operative operation
  • Very flexible task priority assignment
  • Software timers
  • Queues
  • Binary semaphores
  • Counting semaphores
  • Recursive semaphores
  • Mutexes
  • Tick hook functions
  • Idle hook functions
  • Stack overflow checking
  • Trace hook macros

2. FreeRTOS Structure & Hierarchy

• Download sources:

 https://sourceforge.net/projects/freertos/files/FreeRTOS/

FreeRTOS
  ├── Demo             (Contains demo application for every official FreeRTOS port)
  ├── Test             (contains the tests performed on common code and the portable layer code)
  └── Source           //------  (Core FreeRTOS kernel file)   ------//
      ├── include      (Consists of The core FreeRTOS kernel header files)
      └── portable     {==== (Consists of Processor specific code)  ====}
          ├── Compiler (Contains all the ports created by compiler)
          ├── MemMang  (Contains The sample heap implementations)
          └── ...

• Structure & Hierarchy:

FreeRTOS.h
   ├── FreeRTOSConfig.h        (Application specific configuration options)
   ├── projdefs.h              (Basic FreeRTOS definitions)
   └── portable.h              (Definitions specific to the port being used)
         ├── portmacro.h
         └── mpu_wrappers.h

FreeRTOS.h
   ├── list.c
   ├── croutine.c
   ├── timers.c
   ├── heap_?.c
   ├── queue.c
   └── tasks.c

3. Goal

• Understanding various RTOS concepts with FreeRTOS Programming and Debugging
• Using STM32 Standard Peripheral Driver APIs to configure peripherals
• FreeRTOS Debugging using SEGGER SystemView Software
• Using FreeRTOS API with code examples
• Learn Complete Step by step method to run FreeRTOS on STM32 MCUs using OpenSTM32 System Workbench

4. Prepare

Software	Hardware
OpenSTM32 System Workbench	Board NUCLEO-F446RE
SEGGER SystemView	Cable
FreeRTOS v10.1.1	Led
STM32F4 standard peripherals library	Button
minicom

STM32 Boards

• 32F429 { LCD based}
• 32F407G { standard one}
• NUCLEO F446RE {Nucleo board }