FreeRTOS Chapter7 Resource Management

1. Chapter 7
Resource Management

2. Why we need to do this?
• Accessing Peripherals
• Read, Modify, Write Operations
• Non-atomic Access to Variables
• Function Reentrancy

3. Scope
• When and why resource management and
control is necessary.
• What a critical section is.
• What mutual exclusion means.
• What it means to suspend the scheduler.
• How to use a mutex.
• How to create and use a gatekeeper task.
• What priority inversion is, and how priority
inheritance can reduce (but not remove) its
impact.

4. Critical Sections
Lab6-1_TaskMutex
Lab6-2_CriticalSection

5. In the ISR

6. Suspending the Scheduler
Lab6-3_SuspendTask

7. Mutexes (and Binary Semaphores)

8. Mutexes (and Binary Semaphores)
Lab6-4_MutexBinarySemaphore.c

9. Priority Inversion

10. Deadlock (or Deadly Embrace)
Recursive Mutexes
• A task held Mutex, and call other function
need same Mutex……..Who did that stupid
things?
• A, B Task held other’s Semaphores……. I think
the programmer need to study logic.

11. • xSemaphoreCreateMutex()
• xSemaphoreCreateRecursiveMutex()
• xSemaphoreTake()
• xSemaphoreTakeRecursive()
• xSemaphoreGive()
• xSemaphoreGiveRecursive()
Recursive Mutexes

12. Recursive Mutexes - Stuck
Lab6-5_RecursiveMutexesStuck.c
In fact, I don’t think a good engineer
will do this stupid things….
Tell me what kind of situation need
this recursive Mutexes?

13. xSemaphoreCreateRecursiveMutex
Lab6-6_xSemaphoreCreateRecursiveMutex.c

14. Gatekeeper Tasks
Lab6-7_GateKeeperTask.c