FreeRTOS Kernel summary

1. Dispatch mode

FreeRTOS The scheduling methods of are divided into preemptive scheduling and Coprocessor scheduling

• preemptive scheduling ：

  Related to the status and priority of the task ,Freertos There's a Tick Heartbeat clock , It is every 1ms Enter once Tick Interrupt inside , In the interrupt, the current CPU The register of is pushed into the stack allocated by the task , You will find the task with the highest priority in the ready task list （ If tasks of equal priority , Take turns to execute ）, The status of the task is removed from the stack to CPU Register and run .

• Coprocessor scheduling

  Scheduling occurs when the following three conditions are met ：

  1. A task function executes a concession function

  2. A task function called API

  3. The application clearly defines the execution context in interrupts

2. Semaphore

The types of semaphores are divided into binary semaphores and multivalued semaphores according to the number of semaphores , It is often used in applications that control access to shared resources .

3. Mutex semaphore

Mutually exclusive semaphores are mutually exclusive locks , It is divided into ordinary mutexes and recursive mutexes , Apply to multiple mutually exclusive tasks . Pay attention to when using mutually exclusive semaphores , The acquisition of mutually exclusive semaphores must be released , If you don't release , May cause program Deadlock , That is, two tasks acquire the lock owned by each other , Each enters the pending list , Cannot release mutex .

• Common mutex ： You can only get... Once , Duplicate fetch is invalid .

• Recursive mutex ： You can get multiple , But the corresponding must be released many times before the right to use can be ceded .

4. Message queue

For data communication between tasks 、 The data transfer , In the operating system , It is dangerous to transfer data directly using global variables , This article talks about the danger of global variables

5. Event flag set

In addition to semaphores, the synchronization between tasks also includes event flag groups , The synchronization of semaphores is usually one-to-one , Sometimes the system needs many to one synchronization , As for the event flag group, you can check the blog about the use of event flag group in this column .

6. Task to inform

A task notification is an event , Suppose a task is blocked waiting for task notification , After sending a task notification to the receiving task, the blocking state of the task will be released .

This summary refers to ：https://blog.csdn.net/qq_45396672/article/details/120877303?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522165718262116781683971267%2522%252C%2522scm%2522%253A%252220140713.130102334.pc%255Fblog.%2522%257D&request_id=165718262116781683971267&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2_blogfirst_rank_ecpm_v1~rank_v31_ecpm-1-120877303-null-null.185^v2control&utm_term=free&spm=1018.2226.3001.4450