任务调度器代码：
（1）头文件：任务控制块TCB定义、保存任务环境的入栽宏、恢复任务现场的出栽宏。
typedef struct
{
unsigned char* task_stk_top; //保存任务的栽顶
unsigned char task_stack[100];//任务堆栽
}OS_TASK_TCB;
//任务现场保护，保存所有寄存器的宏
#define pushall()
__asm__ __volatile__ ("push r1" "
");
__asm__ __volatile__ ("push r0" "
");
__asm__ __volatile__ ("in r0, 0x3f"
"
");保存CPU状态寄存器
__asm__ __volatile__ ("push r0" "
");
__asm__ __volatile__ ("eor r1, r1"
"
");WINAVR要求R1等于0
__asm__ __volatile__ ("push r2" "
");
__asm__ __volatile__ ("push r3" "
");
__asm__ __volatile__ ("push r4" "
");
__asm__ __volatile__ ("push r5" "
");
__asm__ __volatile__ ("push r6" "
");
__asm__ __volatile__ ("push r7" "
");
__asm__ __volatile__ ("push r8" "
");
__asm__ __volatile__ ("push r9" "
");
__asm__ __volatile__ ("push r10" "
");
__asm__ __volatile__ ("push r11" "
");
__asm__ __volatile__ ("push r12" "
");
__asm__ __volatile__ ("push r13" "
");
__asm__ __volatile__ ("push r14" "
");
__asm__ __volatile__ ("push r15" "
");
__asm__ __volatile__ ("push r16" "
");
__asm__ __volatile__ ("push r17" "
");
__asm__ __volatile__ ("push r18" "
");
__asm__ __volatile__ ("push r19" "
");
__asm__ __volatile__ ("push r20" "
");
__asm__ __volatile__ ("push r21" "
");
__asm__ __volatile__ ("push r22" "
");
__asm__ __volatile__ ("push r23" "
");
__asm__ __volatile__ ("push r24" "
");
__asm__ __volatile__ ("push r25" "
");
__asm__ __volatile__ ("push r26" "
");
__asm__ __volatile__ ("push r27" "
");
__asm__ __volatile__ ("push r28" "
");
__asm__ __volatile__ ("push r29" "
");
__asm__ __volatile__ ("push r30" "
");
__asm__ __volatile__ ("push r31" "
");
//恢复任务现场，弹出所有寄存器的宏
#define popall()
__asm__ __volatile__ ("pop r31" "
");
__asm__ __volatile__ ("pop r30" "
");
__asm__ __volatile__ ("pop r29" "
");
__asm__ __volatile__ ("pop r28" "
");
__asm__ __volatile__ ("pop r27" "
");
__asm__ __volatile__ ("pop r26" "
");
__asm__ __volatile__ ("pop r25" "
");
__asm__ __volatile__ ("pop r24" "
");
__asm__ __volatile__ ("pop r23" "
");
__asm__ __volatile__ ("pop r22" "
");
__asm__ __volatile__ ("pop r21" "
");
__asm__ __volatile__ ("pop r20" "
");
__asm__ __volatile__ ("pop r19" "
");
__asm__ __volatile__ ("pop r18" "
");
__asm__ __volatile__ ("pop r17" "
");
__asm__ __volatile__ ("pop r16" "
");
__asm__ __volatile__ ("pop r15" "
");
__asm__ __volatile__ ("pop r14" "
");
__asm__ __volatile__ ("pop r13" "
");
__asm__ __volatile__ ("pop r12" "
");
__asm__ __volatile__ ("pop r11" "
");
__asm__ __volatile__ ("pop r10" "
");
__asm__ __volatile__ ("pop r9" "
");
__asm__ __volatile__ ("pop r8" "
");
__asm__ __volatile__ ("pop r7" "
");
__asm__ __volatile__ ("pop r6" "
");
__asm__ __volatile__ ("pop r5" "
");
__asm__ __volatile__ ("pop r4" "
");
__asm__ __volatile__ ("pop r3" "
");
__asm__ __volatile__ ("pop r2" "
");
__asm__ __volatile__ ("pop r0" "
");
__asm__ __volatile__ ("out 0x3f, r0" "
");恢复CPU状态寄存器
__asm__ __volatile__ ("pop r0" "
");
__asm__ __volatile__ ("pop r1" "
");
__asm__ __volatile__ ("RETI" "
");
//******************************************************************
（2）主函数main()代码，包括8个任务，调度程序，定义8个任务，每个任务对应一个LED灯的闪烁：
#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>
#include "RTOS.h"
#define LED_PORT PORTA //LED端口定义
#define LED_DDR DDRA
#define LED_PIN PINA
//第1个任务定义
void task1( void )
{
unsigned char temp ;//任务1的局部变量
//在任务1启动节拍定时器
TCCR0 = 0X05;//定时器0初始化
TIMSK = 0X01;
TCNT0 = 0x00;
sei();//打开全局中断
while(1)
{
temp++;
LED_PORT ^=0X01;
for( unsigned char i=0; i<250; i++)
_delay_ms(10);
}
}
//第2个任务定义
void task2(void)
{
while(1)
{
LED_PORT ^=0X02;
for( unsigned char i=0; i<250; i++)
_delay_ms(10);
}
}
//第3个任务定义
void task3(void)
{
while(1)
{
LED_PORT ^=0X04;
for( unsigned char i=0; i<250; i++)
_delay_ms(10);
}
}
//第4个任务定义
void task4(void)
{
while(1)
{
LED_PORT ^=0X08;
for( unsigned char i=0; i<250; i++)
_delay_ms(10);
}
}
//第5个任务定义
void task5(void)
{
while(1)
{
LED_PORT ^=0X10;
for( unsigned char i=0; i<250; i++)
_delay_ms(10);
}
}
//第6个任务定义
void task6(void)
{
while(1)
{
LED_PORT ^=0X20;
for( unsigned char i=0; i<250; i++)
_delay_ms(10);
}
}
//第7个任务定义
void task7(void)
{
while(1)
{
LED_PORT ^=0X40;
for( unsigned char i=0; i<250; i++)
_delay_ms(10);
}
}
//第8个任务定义
void task8(void)
{
while(1)
{
LED_PORT ^=0X80;
for( unsigned char i=0; i<250; i++)
_delay_ms(10);
}
}
//*******************************************************************
volatile unsigned char next_task = 0;//用来指出下一个运行的任务
//计数变量，在定时器0中断函数里加1，用来控制任务切换频率
volatile unsigned char count = 0;
volatile OS_TASK_TCB task_tcb[ 8 ];//定义8个任务的任务控制块TCB数组
//任务堆栽初始化函数，参数为：任务入口地址、任务序号（1-8）
unsigned char* stackinit( void (*task)( void ), unsigned char task_id )
{
unsigned char* stk;
unsigned int temp;
temp = (unsigned int)task;//任务入口地址
stk = &( task_tcb[task_id].task_stack[99] );//取得任务栽顶指针
*stk-- = (unsigned char)(temp&0xff);//将任务入口地址入栽
*stk-- = (unsigned char)(temp>>8);
//以下是CPU所有寄存器初始化，为0值，
*stk-- = (unsigned char)0x00;
/* R0 = 0x00 */
*stk-- = (unsigned char)0x00;
/* R1 = 0x00 */
*stk-- = (unsigned char)0x80;
/* R2 = 0x00 */
*stk-- = (unsigned char)0x00;
/* R3 = 0x00 */
*stk-- = (unsigned char)0x00;
/* R4 = 0x00 */
*stk-- = (unsigned char)0x00;
/* R5 = 0x00 */
*stk-- = (unsigned char)0x00;
/* R6 = 0x00 */
*stk-- = (unsigned char)0x00;
/* R7 = 0x00 */
*stk-- = (unsigned char)0x00;
/* R8 = 0x00 */
*stk-- = (unsigned char)0x00;
/* R9 = 0x00 */
*stk-- = (unsigned char)0x00;
/* R10 = */
*stk-- = (unsigned char)0x00;
/* R11 = */
*stk-- = (unsigned char)0x00;
/* R12 = */
*stk-- = (unsigned char)0x00;
/* R13 = */
*stk-- = (unsigned char)0x00;
/* R14 = */
*stk-- = (unsigned char)0x00;
/* R15 = */
*stk-- = (unsigned char)0x00;
/* R16 = */
*stk-- = (unsigned char)0x00;
/* R17 = */
*stk-- = (unsigned char)0x00;
/* R18 = */
*stk-- = (unsigned char)0x00;
/* R19 = */
*stk-- = (unsigned char)0x00;
/* R20 = */
*stk-- = (unsigned char)0x00;
/* R21 = */
*stk-- = (unsigned char)0x00;
/* R22 = */
*stk-- = (unsigned char)0x00;
/* R23 = */
*stk-- = (unsigned char)0x00;
/* R24 = 0x00 */
*stk-- = (unsigned char)0x00;
/* R25 = 0x00 */
*stk-- = (unsigned char)0x00;
/* R26 = */
*stk-- = (unsigned char)0x00;
/* R27 = */
*stk-- = (unsigned char)0x00;
/* R28 = */
*stk-- = (unsigned char)0x00;
/* R29 = */
*stk-- = (unsigned char)0x00;
/* R30 = */
*stk-- = (unsigned char)0x00;
/* R31 = */
*stk-- = (unsigned char)0x00;
/* SREG = */
return ( (unsigned char*)stk );//返回当前堆栈指针
}
//任务创建函数：
void taskcreat( void (*task)( void ), unsigned char task_id )
{
unsigned char *temp;
temp = stackinit( task, task_id );//堆栽初始化，并返回栽顶指针
//初始化之后将堆栽栽顶指针保存在任务的TCB里，这个变量一直指向栽顶
task_tcb[task_id].task_stk_top = temp;
}
//调度器启动函数，用于运行第一个任务
void OS_Start( void )
{
SP = task_tcb[0].task_stk_top + 33;//堆栽指针指向第一个任务
//用中断返回指令将入口地址弹出到PC指针，运行第一个任务
asm("RETI");
}
//定时器0的中断函数：作周期中断，每次中断，表示当前任务的时间片用完，将结束当前任务，调用下一个任务
//加上下面这句，WINAVR将不保存任何寄存器
void SIG_OVERFLOW0( void ) __attribute__ ( ( signal, naked ) );
SIGNAL( SIG_OVERFLOW0 )
{
pushall( );//自己人工保存所有寄存器
count++; //每次中断加1
if(count>100)//100时任务切换，count值可以调整任务切换频率
{
count = 0;//重新清0
task_tcb[ next_task % 8 ].task_stk_top
=SP;//保存当前任务的栽顶SP指针到当前任务的控制块TCB
next_task++;指向下一个任务
//堆栽指针指向下一个任务栽顶
SP = task_tcb[ next_task % 8
].task_stk_top;
}
popall( );//人工恢复所有寄存器
}
//main()函数
int main( void )
{
//LED灯控制端口设置
LED_PORT=0Xff;
LED_DDR =0Xff;
//创建并初始化8个任务
taskcreat( task1, 0 );
taskcreat( task2, 1 );
taskcreat( task3, 2 );
taskcreat( task4, 3 );
taskcreat( task5, 4 );
taskcreat( task6, 5 );
taskcreat( task7, 6 );
taskcreat( task8, 7 );
OS_Start( );//开始运行任务
while( 1 );
}//****************************************************************