Книга: Real-Time Concepts for Embedded Systems
6.5 Points to Remember
6.5 Points to Remember
Some points to remember include the following:
· Using semaphores allows multiple tasks, or ISRs to tasks, to synchronize execution to synchronize execution or coordinate mutually exclusive access to a shared resource.
· Semaphores have an associated semaphore control block (SCB), a unique ID, a user-assigned value (binary or a count), and a task-waiting list.
· Three common types of semaphores are binary, counting, and mutual exclusion (mutex), each of which can be acquired or released.
· Binary semaphores are either available (1) or unavailable (0). Counting semaphores are also either available (count =1) or unavailable (0). Mutexes, however, are either unlocked (0) or locked (lock count =1).
· Acquiring a binary or counting semaphore results in decrementing its value or count, except when the semaphore’s value is already 0. In this case, the requesting task blocks if it chooses to wait for the semaphore.
· Releasing a binary or counting semaphore results in incrementing the value or count, unless it is a binary semaphore with a value of 1 or a bounded semaphore at its maximum count. In this case, the release of additional semaphores is typically ignored.
· Recursive mutexes can be locked and unlocked multiple times by the task that owns them. Acquiring an unlocked recursive mutex increments its lock count, while releasing it decrements the lock count.
· Typical semaphore operations that kernels provide for application development include creating and deleting semaphores, acquiring and releasing semaphores, flushing semaphore’s task-waiting list, and providing dynamic access to semaphore information.
Оглавление книги
- Chapter 8. The Point-to-Point Protocol
- Chapter 4: Introduction To Real-Time Operating Systems
- Chapter 9: Other RTOS Services
- 1.4 Points to Remember
- 2.5 Points to Remember
- 3.6 Points to Remember
- 4.8 Points to Remember
- 5.7 Points to Remember
- 7.8 Points to Remember
- 8.6 Points to Remember
- 9.4 Points to Remember
- 10.7 Points to Remember