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

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

Un support de cours (en anglais) est remis à chaque stagiaire.
Assistance technique : une assistance par mail et téléphone est aussi assurée pendant les 3 mois qui suivent la session

INFORMATIONS PRATIQUES

Public visé et prérequis :
• Connaissance des concepts C et de la programmation
• Connaissance de base des processeurs embarqués

Lieu :
CCI Nord Isère Parc Technologique
5 rue Condorcet
38 VILLEFONTAINE

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