Multi task foundation of IOT operating system

Multi task basis of IOT operating system

Come back from the weekend to continue studying ！

One . Multitasking fundamentals

1. Multitasking features

Task scheduling mechanism

1. Time slice scheduling mechanism

 The core is time slice polling , Scheduling with the same priority can only be polled by time slice .

2. Preemptive scheduling mechanism

​ When task priorities are inconsistent , Low priority pending , High priority execution first , interrupt （isr） The highest priority is generated .

3. Mission characteristics

​ 1. Programming is simple

​ 2. There is no limit to the number of tasks .

​ 3. Support preemption .

​ 4. Prioritization .

​ 5. Independent stack . When switching tasks, you need to switch CPU Operating environment .（ So the characteristics of the operating system ）

4. The status of the task

​ There are four states in a task ：

1. Pending state ： When the task is suspended , Will not be scheduled by the scheduler .

2. The ready state ： The task will wait for the status of task scheduling when it runs .

3. Blocking state ：osDelay, Give the task a delay , Block him , Then wait for the scheduler to schedule .

4. Running state ：

5. Task priority

2. Multitasking implementation

Every task is done by 3 Part of the implementation

（1） Dead cycle

（2） Task entity

（3） Mission exit : No return value .

void freertosTask(void const * argument){
	for(;;){
	osDelay();
	}
}

Task control block

​ Task control block is a structure that describes task attributes .

3、 ... and 、 Task stack

Two 、 Task creation

1. Create tasks

（1） Task creation API

xTaskCreate();// Create tasks dynamically When using configSUPPORT_DYNAMIC_ALLOCATION Must set 1

xTaskCreateStatic(); When using ConfigSUPPORT_STATIC_ALLICATION Set up 1.

（2） Use cubemax In the task 1s Print the task running flag once

Copy the previous project , Enable the serial port to be configured for asynchronous communication , open FreeRTos Select memory configuration in the configuration options column , It is configured for dynamic and static mixing .

Create serial port task after configuration , Generate keil file .

The project is as follows

（3） Use the key to control Led Task suspend and resume

void vTaskSuspend( TaskHandle_t pxTaskToSuspend ); // Hang up

void vTaskResume( TaskHandle_t pxTaskToResume ); // recovery
Source code ：https://download.csdn.net/download/ay1204/86261003

notes ： Source code comments Part 2