Real-time programming applied to the FreeRTOS operating system

http://www.ac6-training.com/cours.php/cat_FSCA/ref_RT3/

First Day

RTOS Introduction

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

Exercice : Interrupt Management on Cortex-M4

Introduction to Real Time

• Base real time concepts
• The Real Time constraints
• Multi-task and real time

Thread safe data structures

• Need for specific data structures
• Thread safe data structures
  • Linked lists
  • Circular lists
  • FIFOs
  • Stacks
• Data structures integrity proofs
  • Assertions
  • Pre and post-conditions

Exercice : Build a general purpose thread safe linked list

Second Day

Element of a real time system

• 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

Exercice : 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

Exercice : Managing tasks

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

Exercice : Write a simple, thread safe, buddy system memory managerExercice : Write a generic, multi-level, memory managerExercice : Enhance the memory manager for memory error detectionExercice : Detect stack overflow

Third Day

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

Exercice : Synchronizing a task with another one through binary semaphoresExercice : Synchronizing a task with another one through queues

Resource Management

• Mutual Exclusion
  • Spinlocks and interrupt masking
  • Mutex or Semaphore
  • Recursive or not recursive mutexes
  • Priority inversion problem
  • Priority inheritance (the automatic answer)
  • Priority ceiling (the design centric answer)
• Mutual exclusion through FreeRTOS
  • Mutexes and binary semaphores
  • Deadlocks
  • Priority inversion
  • Priority inheritance
• Critical sections
  • Critical sections
  • Suspending (locking) the scheduler
• Gatekeeper tasks

Exercice : Implement mutual exclusion between two tasks

Fourth Day

Parallelism Problems Solution

• Parallel programming problems
  • Uncontrolled parallel access
  • Deadlocks
  • Livelocks
  • Starvation

Exercice : The producer-consumer problem, illustrating (and avoiding) concurrent access problemsExercice : The philosophers dinner problem, illustrating (and avoiding) deadlock, livelock and starvation

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

Exercice : Synchronize Interrupts with tasks

Software Timer

• The Timer Daemon Task
• Timer Configuration
• One-shot / Auto-reload Timer
• Software Timer API

Exercice : Implement Soft Timers

Trouble Shooting

• Checking for stack problems
• Common pitfalls

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

Exercice : Implement protected memory regions