Logo de la rubrique ATELIER : Programmation temps réel avec FreeRTOS pour Coeur ARM Cortex-M

ATELIER : Programmation temps réel avec FreeRTOS pour Coeur ARM Cortex-M

Pour connaitre les prochaines sessions de formation sur Logiciel embarque et programmation cliquez ici.




L’architecture ARM est connue pour offrir un des meilleurs ratios performance/efficacité du marché, tout en consommant très peu d’énergie. Ces architectures ARM ont d’ailleurs pris naturellement possession du marché de la mobilité et équipent l’essentiel des smartphones du marché et de nombreux produits embarqués industriels.

Le noyau temps réel FreeRTOS est particulièrement bien adapté à ces architectures par sa faible empreinte et ses performances.

Objectifs de cet atelier :
• Acquérir une compréhension globale de l’architecture Cortex-M
• Comprendre la mise en œuvre logicielle du Cortex- M et déboguer
• Gérer les interruptions
• Comprendre l’architecture STM32F2
• Découvrir les notions de temps réel multitâches
• Comprendre les vraies contraintes de temps sur les ressources mutuelles
• Comprendre l’architecture de l’OS FreeRTOS
• Découvrir les différents services et API de FreeRTOS
• Apprendre à développer et déboguer les applications FreeRTOS

PROGRAMME

  • First day

Cortex-M Architecture Overview

- V7-M Architecture Overview
- Core Architecture
o Harvard Architecture, I-Code, D-Code and System Bus
o Bit-Banding
o Registers (Two stack pointers)
o States and Privilege Levels
o System Control Block
o Systick Timer
o MPU Overview
- Programming
o Alignment and Endianness
o CMSIS Library
- Exception / Interrupt Mechanism Overview
o Vector Table
o Interrut entry and return Overview
- Tail-Chaining
- Pre-emption (Nesting)
- NVIC Integrated Interrupt Controller
o Exception Priority Management
o Fault escalation
Lab : Becoming familiar with the IDE and clarifying the boot sequence
Lab : Interrupt Management on Cortex-M3 (put in evidence tail-chaining/nesting)

STM32F2 MCUs Architecture Overview

- ARM core based architecture
- Description of STM32F20X SoC architecture
- Clarifying the internal data and instruction paths : Bus Matrix, AHB-lite interconnect, peripheral buses, AHB-to-APB bridges, DMAs
- Memory Organization
o Flash memory read interface
o Adaptive Real-Time memory accelerator, instruction prefetch queue and branch cache
o Sector and mass erase
o Internal SRAMs
- Concurrent access to 112 KB and 16 KB blocks
- SoC mapping
- Flash Programming methods
- Boot Configuration
Lab : Get Metrics for a data copy using the DMA or not

Introduction to Real Time

- Base real time concepts
o The Real Time constraints
o Multi-task and real time
- Introduction to FreeRTOS
- The FreeRTOS source code
o The FreeRTOS architecture and features
o Getting FreeRTOS source code
o Files and directories structure
o Data types and coding style
- Naming conventions
- FreeRTOS on the Cortex/M processors
Lab : Simple FreeRTOS Hello World program

  • Second day

Thread safe data structures
- Need for specific data structures
- Thread safe data structures
o Linked lists
o Circular lists
o FIFOs
o Stacks
- Data structures integrity proofs
o Assertions
o Pre and post-conditions
Lab : Build a general purpose thread safe linked list

Element of a real time system
- Tasks and Task Descriptors
o Content of the task descriptor
o List of task descriptors
- Context Switch
Demo : Analyse a Context Switch
- Task Scheduling and Preemption
o Tick based or tickless scheduling
- Scheduling systems and schedulability proof
o Fixed priorities scheduling
o RMA and EDF scheduling
- FreeRTOS Scheduling
o Deterministic preemptive scheduling
- Scheduling strategies
- Cyclic scheduling (RMA)
- Deadline scheduling
o Cooperative scheduling
- Hybrid scheduling

Task Management
- The Task life-cycle
o Creating tasks
o Deleting tasks
o The Endless-loop pattern
- Task Priorities
o Assigning task priorities
o Changing task priorities
- The idle task
o Idle task hooks
- Timing
- FreeRTOS Debug Capabilities (Hook, Trace)
Lab : Managing tasks, get trace information

Memory Management
- Memory management algorithms
o Buddy System
o Best fit / First Fit
o Pools Management
Demo : Write a simple, thread safe, buddy system memory manager
- FreeRTOS-provided memory allocation schemes
o Allocate-only scheme
o Best-fit without coalescing
o Thread-safe default malloc
o Best-fit alloc and free
- Checking remaining free memory
- Adding an application-specific memory allocator
- Memory management errors
o Stack monitoring
o Dimensioning Stack and Heap
Lab : Detect stack overflow

  • Third day

Synchronization Primitives
- Introduction
o Waiting and waking up tasks
o Semaphores
o Events
o Mailboxes
- FreeRTOS Binary Semaphores
o Take a Binary Semaphore
o Give a Binary Semaphore
Lab : Synchronizing a task with another one through binary semaphores
- FreeRTOS Queues
o Basic use
- Creation
- Sending on a queue
- Receiving from a queue
o Data management
- Sending compound types
- Transfering large data
Lab : Synchronizing a task with another one through queues

Resource Management
- Mutual Exclusion
o Spinlocks and interrupt masking
o Mutex or Semaphore
o Recursive or not recursive mutexes
o Priority inversion problem
- Priority inheritance
- Priority ceiling emulation
- FreeRTOS Mutexes
o Mutexes and binary semaphores
o Deadlocks
o Priority inversion
o Priority inheritance
Lab : Protect a shared resource using mutexes
- Critical sections
o Critical sections
o Suspending (locking) the scheduler
- Gatekeeper tasks
Lab : Implement mutual exclusion between two tasks with critical sections

Parallelism Problems and Solutions
- Parallel programming problems
- Uncontrolled parallel access
Lab : The producer-consumer problem, illustrating (and avoiding) concurrent access problems
- Deadlocks
- Livelocks
- Starvation
Demo : The dining philosophers problem, illustrating (and avoiding) deadlock, livelock and starvation

Interrupt Management
- Deferred interrupt processing with FreeRTOS
o Tasks with interrupt synchronization
o Using semaphores within an ISR
o Counting semaphores
o Using queues within an ISR
- FreeRTOS interrupt processing
o Writing ISRs in C
o Interrupt safe functions
o Interrupt nesting
Lab : Synchronize Interrupts with tasks

Software Timers
- The Timer Daemon Task
- Timer Configuration
- One-shot / Auto-reload Timer
- Software Timer API
Lab : Implement Soft Timers

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