从零开始手写嵌入式实时操作系统

这是B站【黑马程序员】的课程《黑马程序员嵌入式操作系统视频教程，嵌入式入门必学的操作系统教程，从理论到动手实践一套通关》，这套课程的前10节课介绍了一些理论知识，很简单生动，从第11节课开始写代码，从零开始手写嵌入式实时操作系统。这篇笔记主要针对嵌入式实时操作系统demo代码编写。

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目录

1 声明两个任务的堆栈指针和任务堆栈

2 定义操作系统的loadtask函数

3 通过修改SP，来修改调用的函数

4 任务调度器的实现

5 任务切换的上下文混淆问题

6 多任务访问外设操作（LED）

7 为什么延时1秒会出现睡眠2秒的问题

8 改用硬件delay实现sleep函数

9 操作系统监管定期时间片轮转

10 最终代码

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1 声明两个任务的堆栈指针和任务堆栈

#include <stc8h.h>#define MAX_TASKS 2    //为了简化，假设当前操作系统只有两个task
#define MAX_TASKS_DEP 32    //每个task任务的堆栈深度为32unsigned char task_sp[MAX_TASKS];    //任务的堆栈指针，即当前系统的两个堆栈指针
unsigned char task_stack[MAX_TASKS][MAX_TASKS_DEP];

2 定义操作系统的loadtask函数

#include <stc8h.h>#define MAX_TASKS 2 
#define MAX_TASKS_DEP 32 //idata关键字指明这两个变量在stc8单片机访问最快的内部内存中
unsigned char idata task_sp[MAX_TASKS];
unsigned char idata task_stack[MAX_TASKS][MAX_TASKS_DEP];unsigned char task_id;    //当前任务号，从0开始//第0号任务
void task0()
{unsigned int a = 3;while (1){a = a + 3;}
}//第1号任务
void task1()
{unsigned int b = 5;while (1){b = b + 5;}
}//操作系统加载任务的函数
//参数说明：
//    fn：是一个函数的指针，数据类型为int，stc8单片机中函数指针为16位
//    tid：表示task id
//函数作用：
//    把一个task的函数指针放入对应的堆栈空间里面
void task_load(unsigned int fn, unsigned char tid)
{task_sp[tid] = task_stack[tid] + 1;    //把任务的指针往下一个空间挪一格task_stack[tid][0] = fn & 0xff;    //task_stack[tid][0]放上fn函数指针的低8位task_stack[tid][1] = fn >> 8;    //task_stack[tid][1]放上fn函数指针的高8位
}

3 通过修改SP，来修改调用的函数

#include <stc8h.h>#define MAX_TASKS 2 
#define MAX_TASKS_DEP 32 unsigned char idata task_sp[MAX_TASKS];
unsigned char idata task_stack[MAX_TASKS][MAX_TASKS_DEP];unsigned char task_id; void task0()
{unsigned int a = 3;while (1){a = a + 3;}
}void task1()
{unsigned int b = 5;while (1){b = b + 5;}
}void task_load(unsigned int fn, unsigned char tid)
{task_sp[tid] = task_stack[tid] + 1;task_stack[tid][0] = fn & 0xff;task_stack[tid][1] = fn >> 8;
}int main()
{task_load(task0, 0);    //把task0装载到内存中task_id = 0;SP = task_sp[0];    //修改StackPointer寄存器的值为task_sp[0]的地址，执行task0函数
}

4 任务调度器的实现

#include <stc8h.h>#define MAX_TASKS 2 
#define MAX_TASKS_DEP 32 unsigned char idata task_sp[MAX_TASKS];
unsigned char idata task_stack[MAX_TASKS][MAX_TASKS_DEP];unsigned char task_id; //定义一个任务切换的函数（任务调度器）
void task_switch()
{task_sp[task_id] = SP;    //把当前系统的堆栈指针存放到某个任务的task_sp里task_id = task_id + 1;//防止task_id溢出if (task_id == MAX_TASKS){task_id = 0;}SP = task_sp[task_id];
}void task0()
{unsigned int a = 3;while (1){a = a + 3;task_switch();    //任务切换}
}void task1()
{unsigned int b = 5;while (1){b = b + 5;task_switch();    //任务切换}
}void task_load(unsigned int fn, unsigned char tid)
{task_sp[tid] = task_stack[tid] + 1;task_stack[tid][0] = fn & 0xff;task_stack[tid][1] = fn >> 8;
}int main()
{task_load(task0, 0);task_id = 0;SP = task_sp[0];
}

5 任务切换的上下文混淆问题

void task0()
{static unsigned int a = 3;    //编译器将其放在静态数据区域，这样不会出现数据脏读的现象while (1){a = a + 3;task_switch();}
}void task1()
{static unsigned int b = 5;    //编译器将其放在静态数据区域，这样不会出现数据脏读的现象while (1){b = b + 5;task_switch(); }
}

6 多任务访问外设操作（LED）

#include <intrins.h>//软件生成
//24MHZ的主频下，延时1s的函数
void Delay1000ms()
{unsigned char i, j, k;_nop_();_nop_();i = 122;j = 193;k = 128;do{do{    while(--k);}while (--j)} while (--i)
}void task0()
{//亮灯P5M0 = 0x00;P5M1 = 0x00;P53 = 1;while (1){//延迟1sDelay1000ms();//熄灯P53 = ~P53;task_switch();}
}void task1()
{//亮灯P4M1 = 0x00;P4M0 = 0x00;P2M1 = 0x00;P2M0 = 0x00;P27 = 1;while (1){//延迟1sDelay1000ms();//熄灯P27 = ~P27;task_switch(); }
}int main()
{task_load(task0, 0);task_load(task1, 1);task_id = 0;SP = task_sp[0];
}

7 为什么延时1秒会出现睡眠2秒的问题

因为软件实现的软delay占用了cpu的时间。

8 改用硬件delay实现sleep函数

#include <intrins.h>//枚举任务状态
typedef enum {TASK_RUNNING,    //运行状态TASK_SUSPENDED,  //挂起状态
} TaskStatus;typedef struct {unsigned char id;    //任务idTaskStatus status;   //任务状态unsigned int delay_count;    //延迟计数器unsigned int delay_duration; //延迟时间
} Task；//两个任务都是默认运行状态，不延时
Task idata tasks[MAX_TASKS] = {{0, TASK_RUNNING, 0, 0},{0, TASK_RUNNING, 0, 0}
};//原型函数
void Timer0_init();
void sleep(unsigned int , unsigned int );//睡眠函数
void sleep(unsigned int task_id, unsigned int delay_ms)
{tasks[task_id].status = TASK_SUSPENDED;tasks[task_id].delay_count = 0;tasks[task_id].delay_duration = delay_ms;
}//软件生成
//24MHZ主频下，硬件delay1ms
void Timer0_init()
{AUXR |= 0x80;TMOD &= 0xF0;TL0 = 0x40;TH0 = 0xA2;TF0 = 2;TR0 = 1;
}//系统的定时器中断，每隔1ms就执行一次中断函数
void Timer0_ISR(void) interrupt 1
{unsigned char i = 0;for (i = 0; i < MAX_TASKS; i++){//睡眠状态if (tasks[i].status == TASK_SUSPENDED){tasks[task_id].delay_count++;}//睡眠结束if (tasks[i].delay_count == tasks[task_id].delay_duration){//睡眠结束tasks[i].status = TASK_RUNNING;tasks[i].delay_count = 0;}}
}void task0()
{P5M0 = 0x00;P5M1 = 0x00;P53 = 1;while (1){//检查自己的状态，如果自己是睡眠状态，就应该交给别的task去做if (tasks[0].status == TASK_SUSPENDED){task_switch();continue();}//硬件延迟1ssleep(0, 1000);P53 = ~P53;task_switch();}
}void task1()
{P4M1 = 0x00;P4M0 = 0x00;P2M1 = 0x00;P2M0 = 0x00;P27 = 1;while (1){//检查自己的状态，如果自己是睡眠状态，就应该交给别的task去做if (tasks[1].status == TASK_SUSPENDED){task_switch();continue();}//硬件延迟1ssleep(1, 1000);P27 = ~P27;task_switch(); }
}int main()
{Timer0_init();task_load(task0, 0);task_load(task1, 1);task_id = 0;SP = task_sp[0];
}

9 操作系统监管定期时间片轮转

//在24Mhz下，设置定时器为100ms
void Timer1_Init(void)
{AUXR |= 0x40;TMOD &= 0x0F;TL1 = 0xA0;TH1 = 0xF6;TF1 = 0;TR1 = 1;
}//在timer1中的中断，每100ms进行任务切换
void Timer1_ISR(void) interrupt 1
{task_switch(); 
}int main()
{Timer0_init();Timer1_init();task_load(task0, 0);task_load(task1, 1);task_id = 0;SP = task_sp[0];
}

10 最终代码

#include <intrins.h>#include <stc8h.h>#define MAX_TASKS 2 
#define MAX_TASKS_DEP 32 unsigned char idata task_sp[MAX_TASKS];
unsigned char idata task_stack[MAX_TASKS][MAX_TASKS_DEP];unsigned char task_id; typedef enum {TASK_RUNNING,   TASK_SUSPENDED, 
} TaskStatus;typedef struct {unsigned char id;  TaskStatus status;  unsigned int delay_count;   unsigned int delay_duration; 
} Task；Task idata tasks[MAX_TASKS] = {{0, TASK_RUNNING, 0, 0},{0, TASK_RUNNING, 0, 0}
};void task_switch()
{task_sp[task_id] = SP;  task_id = task_id + 1;if (task_id == MAX_TASKS){task_id = 0;}SP = task_sp[task_id];
}void Timer0_init();
void sleep(unsigned int , unsigned int );void sleep(unsigned int task_id, unsigned int delay_ms)
{tasks[task_id].status = TASK_SUSPENDED;tasks[task_id].delay_count = 0;tasks[task_id].delay_duration = delay_ms;
}void Timer0_init()
{AUXR |= 0x80;TMOD &= 0xF0;TL0 = 0x40;TH0 = 0xA2;TF0 = 2;TR0 = 1;
}void Timer0_ISR(void) interrupt 1
{unsigned char i = 0;for (i = 0; i < MAX_TASKS; i++){if (tasks[i].status == TASK_SUSPENDED){tasks[task_id].delay_count++;}if (tasks[i].delay_count == tasks[task_id].delay_duration){tasks[i].status = TASK_RUNNING;tasks[i].delay_count = 0;}}
}void Timer1_Init(void)
{AUXR |= 0x40;TMOD &= 0x0F;TL1 = 0xA0;TH1 = 0xF6;TF1 = 0;TR1 = 1;
}void Timer1_ISR(void) interrupt 1
{task_switch(); 
}void task0()
{P5M0 = 0x00;P5M1 = 0x00;P53 = 1;while (1){if (tasks[0].status == TASK_SUSPENDED){task_switch();continue();}sleep(0, 1000);P53 = ~P53;task_switch();}
}void task1()
{P4M1 = 0x00;P4M0 = 0x00;P2M1 = 0x00;P2M0 = 0x00;P27 = 1;while (1){if (tasks[1].status == TASK_SUSPENDED){task_switch();continue();}sleep(1, 1000);P27 = ~P27;task_switch(); }
}int main()
{Timer0_init();Timer1_init();task_load(task0, 0);task_load(task1, 1);task_id = 0;SP = task_sp[0];
}