Cub school learning - Kernel Development

One   task management

Basic concepts

1、 From a systematic point of view , The task is to compete for the smallest running unit of system resources . Tasks can be used or wait CPU、 Use system resources such as memory space , And alone Run on other tasks .

2、LiteOS The task module can provide users with multiple tasks , It realizes the switching and communication between tasks , Help users manage business process . So the user You can put more energy into the implementation of business functions .

3、LiteOS The task in is preemptive scheduling mechanism , High priority tasks can interrupt low priority tasks , Low priority tasks must be blocked or blocked by high priority tasks You can't get scheduling until it's over , At the same time, it supports time slice rotation scheduling .

4、LiteOS The default tasks are 32 Priority (0-31), The highest priority is 0, The lowest priority is 31

Task status

be ready ： The task is on the ready list , Just wait CPU.

function ： The task is in progress .

Blocking ： The task is not on the ready list . Include task is suspended 、 The task is delayed 、 The task is waiting for semaphores 、 Read / write queues or wait for write continuation events .

Exit state ： The task is finished , Wait for the system to recycle resources .

Other concepts related to the task

Mission ID: It is returned to the user through parameters when the task is created , As a very important indicator of the task

Task priority : Priority indicates the priority of task execution .

Task entry function ​: Function to be executed after each new task is scheduled .

Task control block TCB: Each task contains a task control block (TCB).TCB Contains task context stack pointer (stack pointer) 、 Task status 、 Task priority 、 Mission ID、 Task name 、 Task stack size and other information .TCB It can reflect the operation of each task .

Task stack : Each task has an independent stack space , We call it the task stack .

Task context : Some resources used in the running process of the task , Such as register, etc , We call it task context .LiteOS When the task is suspended, Ben The task of the task . Context information , Save it in your own task stack , So that when the mission resumes , Recover the suspended context information from the stack space , So as to continue to implement Code that is broken when a line is suspended .

Task switching : Task switching includes getting the highest priority task in the ready list 、 Cut out the task context to save 、 Cut in task context recovery and other actions .

Task mobilization mechanism

Description of task status migration :

The ready state → Running state : After the task is created, it enters ready state , When task switching occurs , The highest priority task in the ready list is executed , So as to enter into operation state , But the task is still on the ready list .

Running state → Blocking state : Task run suspended due to 、 Read semaphore, wait, etc , Deleted from the ready list and blocked .

Blocking state → The ready state ( Blocking state → Running state ) : When blocked tasks are restored ( Mission recovery 、 Delay time out 、 Read semaphore timeout or read semaphore, etc ), The recovered tasks will be added to the ready list , Thus, the blocking state becomes ready state ; At this time, if the priority of the recovered task is higher than that of the running task level , Task switching will occur , Change the task from ready state to running state .

The ready state → Blocking state : The task may also be blocked in the ready state ( Hang up ).

Running state → The ready state : After a higher priority task is created or restored , Enter the ready list after task switching .

Running state → Exit state : End of task operation , The kernel automatically removes this task , At this time, it changes from running state to exit state .

Blocking state → Exit state : Blocked task call delete interface , The task state changes from blocking state to exit state .