一个简单的51单片机操作系统的实现

复习到操作系统这本书，在看到进程管理的时候，想起以前费了相当大的时间去做一个属于自己的操作系统，结果什么都没弄出来。

趁着看到这个章节，又一次地萌生了这个想法，于是网上各种寻找资料。发现现在的大多数操作系统都已经比较完善，换而言之，就是太庞大。无法去理解，无法自己照搬原文去弄一个属于自己的操作系统出来。

机缘偶得之下，发现了一篇关于在单片机下面实现一个实时操作系统的文章， 即《建立一个属于自己的AVR的RTOS》，这篇文章比起讲什么操作系统原理、unix内核分析、linux内核分析、xx内核分析等等来说，简单明了了很多(有兴趣的同学们可以去研究一下这篇文章)。在参考这篇文章以及在51单片机下面使用汇编语言编程，以及众多网上资料之后。总结地写出了一个"在51单片机下具有延时功能占先式内核的操作系统“，并仿真成功，加深了我对操作系统这个东西的小小理解。下面附上程序代码以及实现。
如果网页复制代码有错误，操作系统的完整代码请从这里下载：http://www.51hei.com/f/12545.rar

以下是部分代码：

#include regx52.h>#define MAX_TASKS 5typedef struct os_task_control_table {unsigned char os_task_wait_tick;unsigned char os_task_stack_top;}TCB;volatile unsigned char int_count;volatile unsigned char os_en_cr_count;#define enter_int() EA=0;int_count++;#define os_enter_critical() EA=0;os_en_cr_count++;#define os_exit_critical() if(os_en_cr_count>=1)

{os_en_cr_count--;if(os_en_cr_count==0)EA=1;}unsigned char code os_map_tbl[] = {0x01, 0x02, 0x04,

 0x08, 0x10, 0x20, 0x40, 0x80};volatile unsigned char os_task_int_tbl;idata volatile TCB os_tcb[MAX_TASKS];volatile unsigned char os_task_running_id;volatile unsigned char os_task_rdy_tbl;unsigned char idata os_task_stack[MAX_TASKS][20];void os_init(void);void os_task_create(unsigned char task_id ,

unsigned int task_point,unsigned char stack_point);void os_delay(unsigned char ticks);void os_start(void);void os_task_switch(void);void exit_int(void);void os_init(void) {EA = 0;ET2 = 1;T2CON = 0X00;T2MOD = 0X00;RCAP2H = 0x0D8;RCAP2L = 0x0F0;os_task_rdy_tbl = 0;os_task_int_tbl = 0xff;int_count = 0;os_en_cr_count = 0;}void os_task_create(unsigned char task_id ,

unsigned int task_point,unsigned char stack_point) {os_enter_critical();((unsigned char idata *)stack_point)[0] = task_point;((unsigned char idata *)stack_point)[1] = task_point>>8;os_tcb[task_id].os_task_stack_top = stack_point+14;os_task_rdy_tbl |= os_map_tbl[task_id];os_tcb[task_id].os_task_wait_tick = 0;os_exit_critical();}void os_delay(unsigned char ticks) {os_enter_critical();os_tcb[os_task_running_id].os_task_wait_tick = ticks;os_task_rdy_tbl = ~os_map_tbl[os_task_running_id];os_exit_critical();os_task_switch();}void os_start(void) {os_task_running_id = 0;os_tcb[os_task_running_id].os_task_stack_top -= 13;EA = 1;SP = os_tcb[os_task_running_id].os_task_stack_top;TR2 = 1;}void os_task_switch(void) {unsigned char i;EA = 0;os_tcb[os_task_running_id].os_task_stack_top = SP;os_task_int_tbl = ~os_map_tbl[os_task_running_id];for(i=0; iMAX_TASKS; i++) {if(os_task_rdy_tblos_map_tbl[i]) {break;}}os_task_running_id = i;SP = os_tcb[os_task_running_id].os_task_stack_top;if(os_task_int_tblos_map_tbl[os_task_running_id]) {__asm POP 7__asm POP 6 //恢复任务寄存器__asm POP 5__asm POP 4__asm POP 3__asm POP 2__asm POP 1__asm POP 0__asm POP PSW__asm POP DPL__asm POP DPH__asm POP B__asm POP ACC}EA = 1;__asm RETI}void exit_int(void) {unsigned char i;SP -= 2;if(--int_count == 0) {os_tcb[os_task_running_id].os_task_stack_top = SP;os_task_int_tbl |= os_map_tbl[os_task_running_id];for(i=0; iMAX_TASKS; i++) {if(os_task_rdy_tblos_map_tbl[i]) {break;}}os_task_running_id = i;SP = os_tcb[os_task_running_id].os_task_stack_top;if(os_task_int_tblos_map_tbl[os_task_running_id]) {__asm POP 7__asm POP 6 //恢复任务寄存器__asm POP 5__asm POP 4__asm POP 3__asm POP 2__asm POP 1__asm POP 0__asm POP PSW__asm POP DPL__asm POP DPH__asm POP B__asm POP ACC}EA = 1;__asm RETI}__asm POP 7__asm POP 6 //恢复任务寄存器__asm POP 5__asm POP 4__asm POP 3__asm POP 2__asm POP 1__asm POP 0__asm POP PSW__asm POP DPL__asm POP DPH__asm POP B__asm POP ACCEA=1;__asm RETI}void timer2_isr(void) interrupt 5 {unsigned char i;TF2=0;enter_int();for(i=0; iMAX_TASKS; i++) {if(os_tcb[i].os_task_wait_tick) {os_tcb[i].os_task_wait_tick--;if(os_tcb[i].os_task_wait_tick == 0) {os_task_rdy_tbl |= os_map_tbl[i];}}}exit_int();}void task_0(void) {while(1) {}}sbit seg2 = P2^5;sbit seg3 = P2^6;sbit seg4 = P2^7;void delay_ms(unsigned int xms){unsigned int x,y;for(x=xms; x>0; x--)for(y=248; y>0; y--);}unsigned char code table[]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,

0x07,0x7f,0x6f,0x77,0x7c,0x39,0x5e,0x79,0x71,0x40,0};void task_1(void) {unsigned char gw,sw,bw;while(1) {bw = os_tcb[2].os_task_wait_tick/100;sw = os_tcb[2].os_task_wait_tick%100/10;gw = os_tcb[2].os_task_wait_tick%10;P0 = table[bw];seg2=0;delay_ms(3);seg2=1;P0 = table[sw];seg3=0;delay_ms(3);seg3=1;P0 = table[gw];seg4=0;delay_ms(3);seg4=1;}}void task_2(void) {unsigned char i;while(1) {i++;P3 = 0x01(i%8);os_delay(200);}}void task_3(void) {unsigned char i;while(1) {i++;//P2 = 0x01(i%8);os_delay(7);}}void task_4(void) {unsigned char i;while(1) {i++;P1 = 0x01(i%8);os_delay(10);}}void main(void) {os_init();os_task_create(4,(unsigned int)task_0,(unsigned char)os_task_stack[4]);os_task_create(3,(unsigned int)task_1,(unsigned char)os_task_stack[3]);os_task_create(2,(unsigned int)task_2,(unsigned char)os_task_stack[2]);os_task_create(1,(unsigned int)task_3,(unsigned char)os_task_stack[1]);os_task_create(0,(unsigned int)task_4,(unsigned char)os_task_stack[0]);os_start();}