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RT3 FreeRTOS Real Time Programming

Real-time programming applied to the FreeRTOS operating system

formateur
Objectives
  • Get an overview on Cortex-M4 architecture
  • Discover the concepts of real time multitasking
  • Understand Real Time constraints
    • Determinism
    • Preemption
    • Interrupts
  • Understand the FreeRTOS architecture
  • Discover the various FreeRTOS services and APIs
  • Learn how to develop FreeRTOS applications
  • Learn how to debug FreeRTOS applications
Course environment
  • Convenient course material with space for taking notes
  • Example code, labs and solutions
  • A PC under Windows 7 for two trainees
  • A ST STM32F4 (Cortex/M4) with System Workbench IDE
Prerequisites
  • Familiarity with embedded C concepts and programming
  • Basic knowledge of embedded processors

First Day
Cortex-M resources used by RTOS
  • Cortex-M Architecture Overview
    • Two stacks pointers
    • Different Running-modes and Privileged Levels
    • MPU Overview
    • Systick Timer Description
  • Exception / Interrupt Mechanism Overview
    • Interrut entry and return Overview
    • SVC / PendSV / Systick Interrupt Presentation
  • Developing with the IDE
Exercise :  Interrupt Management on Cortex-M4
Element of a real time system
  • Base real time concepts
  • The Real Time constraints
  • Multi-task and real time
  • Tasks and Task Descriptors
    • Content of the task descriptor
    • List of task descriptors
  • Context Switch
  • Task Scheduling and Preemption
    • Tick based or tickless scheduling
  • Scheduling systems and schedulability proof
    • Fixed priorities scheduling
    • RMA and EDF scheduling
  • Scheduling through FReeRTOS
    • Deterministic preemptive scheduling
    • Scheduling strategies
    • Cooperative scheduling
    • Hybrid scheduling
Exercise :  Analyse a Context Switch
Task Management
  • The Task life-cycle
    • Creating tasks
    • Deleting tasks
    • The Endless-loop pattern
  • Task Priorities
    • Assigning task priorities
    • Changing task priorities
  • The idle task
    • Idle task hooks
  • Timing
Exercise :  Managing tasks
Second Day
FreeRTOS Memory Management
  • FreeRTOS Memory Managers
  • Out of Memory management
  • Stack Overflow Management
Exercise :  Check stack usage in existing programs
Resource Management
  • Mutual exclusion through FreeRTOS
    • Critical sections (interrupt masking)
    • Suspending (locking) the scheduler
    • Mutexes
  • Mutexes concepts
    • Mutex or Semaphore
    • Recursive or not recursive mutexes
    • Priority inversion problem
    • Priority inheritance (the automatic answer)
    • Priority ceiling (the design centric answer)
  • Gatekeeper tasks
Exercise :  Implement mutual exclusion between tasks
Synchronization Primitives
  • Introduction
    • Waiting and waking up tasks
    • Semaphores
    • Events
    • Mailboxes
  • Binary Semaphores through FreeRTOS
    • Give a Binary Semaphore
    • Take a binary Semaphore
  • Queue Management through FreeRTOS
    • Creation
    • Sending on a queue
    • Receiving from a queue
    • Data management
    • Sending compound types
    • Transfering large data
  • Event groups
  • Task Notifications
  • Stream Buffers and Message Buffers
Exercise :  Synchronizing a task with another one through binary semaphores
Exercise :  Synchronizing a task with another one through queues
Exercise :  Task Notifications
Exercise :  Properly use stream Buffers
Exercise :  Message Buffers
Parallelism Problems Solution
  • Parallel programming problems
    • Uncontrolled parallel access
    • Deadlocks
    • Livelocks
    • Starvation
Exercise :  The producer-consumer problem, illustrating (and avoiding) concurrent access problems
Exercise :  The philosophers dinner problem, illustrating (and avoiding) deadlock, livelock and starvation
Third Day
Interrupt Management
  • Need for interrupts in a real time system
    • Software Interrupt
    • Time Interrupts
    • Device Interrupts
  • Level or Edge interrupts
  • Hardware and Software acknowledge
  • Interrupt vectoring
  • Interrupts and scheduling
  • Deferred interrupt processing through FreeRTOS
    • Tasks with interrupt synchronization
    • Using semaphores within an ISR
    • Counting semaphores
    • Using queues within an ISR
  • FreeRTOS interrupt processing
    • Writing ISRs in C
    • Interrupt safe functions
    • Interrupt nesting
Exercise :  Synchronize Interrupts with tasks
Software Timer
  • The Timer Daemon Task
  • Timer Configuration
  • One-shot / Auto-reload Timer
  • Software Timer API
  • Deferred interrupt handling
Exercise :  Implement Soft Timers
FreeRTOS-MPU
  • The Cortex/M MPU
    • User and privileged modes
    • Access permissions
  • Defining MPU regions
    • Overlapping regions
    • Predefined regions
    • Programmer-defined regions
  • Needed linker configuration
  • Practical usage tips
Exercise :  Implement protected memory regions
Annexes
Data structures
  • Need for specific data structures
  • Data structures
    • Linked lists
    • Circular lists
    • FIFOs
    • Stacks
  • Data structures integrity proofs
    • Assertions
    • Pre and post-conditions
  • Thread safety
Exercise :  Build a general purpose linked list
Memory Management
  • Memory management algorithms
    • Buddy System
    • Best fit / First Fit
    • Pools Management
  • FreeRTOS-provided memory allocation schemes
    • Allocate-only scheme
    • Best-fit without coalescing
    • Thread-safe default malloc
  • Checking remaining free memory
  • Adding an application-specific memory allocator
  • Memory management errors
  • Stack monitoring
Exercise :  Write a simple, thread safe, buddy system memory manager
Exercise :  Write a generic, multi-level, memory manager
Exercise :  Enhance the memory manager for memory error detection