freertos实时操作系统空闲任务阻塞延时示例解析

#define portSTACK_TYPE	uint32_t
typedef portSTACK_TYPE StackType_t;

#define configMINIMAL_STACK_SIZE	( ( unsigned short ) 128 )
StackType_t IdleTaskStack[configMINIMAL_STACK_SIZE];

TCB_t IdleTaskTCB;

typedef struct tskTaskControlBlock
{
	volatile StackType_t    *pxTopOfStack;    

	ListItem_t			    xStateListItem;   
    
    StackType_t             *pxStack; 
	                                          
	char     pcTaskName[ configMAX_TASK_NAME_LEN ];

    TickType_t xTicksToDelay; 
} tskTCB;
typedef tskTCB TCB_t;


void vApplicationGetIdleTaskMemory( TCB_t **ppxIdleTaskTCBBuffer, 
                                    StackType_t **ppxIdleTaskStackBuffer, 
                                    uint32_t *pulIdleTaskStackSize )
{
		*ppxIdleTaskTCBBuffer=&IdleTaskTCB;//空闲任务的任务控制块
		*ppxIdleTaskStackBuffer=IdleTaskStack; //空闲任务的任务栈
		*pulIdleTaskStackSize=configMINIMAL_STACK_SIZE;//栈的大小
}
void vTaskStartScheduler( void )
{
     

    TCB_t *pxIdleTaskTCBBuffer = NULL;               
    StackType_t *pxIdleTaskStackBuffer = NULL;       
    uint32_t ulIdleTaskStackSize;
    
    
    vApplicationGetIdleTaskMemory( &pxIdleTaskTCBBuffer, 
                                   &pxIdleTaskStackBuffer, 
                                   &ulIdleTaskStackSize );    
    
    xIdleTaskHandle = xTaskCreateStatic( (TaskFunction_t)prvIdleTask,              
					                     (char *)"IDLE",                           
					                     (uint32_t)ulIdleTaskStackSize ,           
					                     (void *) NULL,                            
					                     (StackType_t *)pxIdleTaskStackBuffer,     
					                     (TCB_t *)pxIdleTaskTCBBuffer );           
                                     
    vListInsertEnd( &( pxReadyTasksLists[0] ), &( ((TCB_t *)pxIdleTaskTCBBuffer)->xStateListItem ) );
    

                                         
    
    pxCurrentTCB = &Task1TCB;
    
    xTickCount = ( TickType_t ) 0U;
    
    if( xPortStartScheduler() != pdfALSE )
    {
        
    }
}
//下面是空闲任务的任务入口，看到，里面什么都没做
//这个我用debug发现一直卡到这个for不动了。
//通过单步运行，发生了中断，程序也无法进入中断。
static portTASK_FUNCTION( prvIdleTask, pvParameters )
{
	
	( void ) pvParameters;
    for(;;)
    {
        
    }
}

void Task1_Entry( void *p_arg )
{
	for( ;; )
	{
#if 0        
		flag1 = 1;
		delay( 100 );		
		flag1 = 0;
		delay( 100 );
		
        portYIELD();
#else
		flag1 = 1;
        vTaskDelay( 2 );		
		flag1 = 0;
        vTaskDelay( 2 );
#endif        
	}
}

void vTaskDelay( const TickType_t xTicksToDelay )
{
    TCB_t *pxTCB = NULL;
    
    pxTCB = pxCurrentTCB;
    
    pxTCB->xTicksToDelay = xTicksToDelay;
    
    taskYIELD();
}

#define portNVIC_INT_CTRL_REG		( * ( ( volatile uint32_t * ) 0xe000ed04 ) )
#define portNVIC_PENDSVSET_BIT		( 1UL << 28UL )
#define portSY_FULL_READ_WRITE		( 15 )

#define portYIELD()																\
{																				\
									\
	portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;								\																				\
							\
	__dsb( portSY_FULL_READ_WRITE );											\
	__isb( portSY_FULL_READ_WRITE );											\
}

__asm void xPortPendSVHandler( void )
{
//	extern uxCriticalNesting;
	extern pxCurrentTCB;
	extern vTaskSwitchContext;
	PRESERVE8
    
    
	mrs r0, psp
	isb
	ldr	r3, =pxCurrentTCB		
	ldr	r2, [r3]                

	stmdb r0!, {r4-r11}			
	str r0, [r2]                				
                               	stmdb sp!, {r3, r14}        
	mov r0, #configMAX_SYSCALL_INTERRUPT_PRIORITY    
	msr basepri, r0
	dsb
	isb
	bl vTaskSwitchContext        
	mov r0, #0                  
	msr basepri, r0
	ldmia sp!, {r3, r14}        
	ldr r1, [r3]
	ldr r0, [r1] 				
	ldmia r0!, {r4-r11}			
	msr psp, r0
	isb
	bx r14                      
	nop
}

void vTaskSwitchContext( void )
{
	if( pxCurrentTCB == &IdleTaskTCB )//如果当前线程是空闲线程
	{
		if(Task1TCB.xTicksToDelay == 0)//如果线程1延时时间结束
		{            
            pxCurrentTCB =&Task1TCB;//切换到线程1
		}
		else if(Task2TCB.xTicksToDelay == 0)//如果线程2延时时间结束(线程1在延时中)
		{
            pxCurrentTCB =&Task2TCB;//切换到线程2
		}
		else
		{
			return;		
		} 
	}
	else//当前任务不是空闲任务
	{
		if(pxCurrentTCB == &Task1TCB)//如果当前线程是线程1
		{
			if(Task2TCB.xTicksToDelay == 0)//如果线程2不在延时中
			{
                pxCurrentTCB =&Task2TCB;//切换到线程2
			}
			else if(pxCurrentTCB->xTicksToDelay != 0)//如果线程1进入延时状态(线程2也在延时中)
			{
                pxCurrentTCB = &IdleTaskTCB;//切换到空闲线程
			}
			else 
			{
				return;		
			}
		}
		else if(pxCurrentTCB == &Task2TCB)//如果当前线程是线程2
		{
			if(Task1TCB.xTicksToDelay == 0)//如果线程1不在延时中
			{
                pxCurrentTCB =&Task1TCB;//切换到线程1
			}
			else if(pxCurrentTCB->xTicksToDelay != 0)//如果线程2进入延时状态(线程1也在延时中)
			{
                pxCurrentTCB = &IdleTaskTCB;//切换到空闲线程
			}
			else 
			{
				return;		
			}
		}
	}
}

//main函数里面
    
    vTaskStartScheduler();  
//task.c里面调用了xPortStartScheduler函数
void vTaskStartScheduler( void )
{
    //.....省略部分代码
    
    if( xPortStartScheduler() != pdFALSE )
    {
        
    }
}
//port.c里面
//xPortStartScheduler调度器启动函数，里面调用了vPortSetupTimerInterrupt函数初始化SysTick
BaseType_t xPortStartScheduler( void )
{
    
	portNVIC_SYSPRI2_REG |= portNVIC_PENDSV_PRI;
	portNVIC_SYSPRI2_REG |= portNVIC_SYSTICK_PRI;
    
    vPortSetupTimerInterrupt();
	
	prvStartFirstTask();
	
	return 0;
}
//system_ARMCM4.c文件
#define  XTAL            (50000000UL)     
#define  SYSTEM_CLOCK    (XTAL / 2U)
//FreeRTOSConfig.h文件
//系统时钟大小
#define confiGCPU_CLOCK_HZ			( ( unsigned long ) 25000000 )	
//SysTick每秒中断多少次，配置成100，10ms中断一次
#define configTICK_RATE_HZ			( ( TickType_t ) 100 )
//下面初始化SysTick

#define portNVIC_SYSTICK_CTRL_REG			( * ( ( volatile uint32_t * ) 0xe000e010 ) )

#define portNVIC_SYSTICK_LOAD_REG			( * ( ( volatile uint32_t * ) 0xe000e014 ) )

#ifndef configSYSTICK_CLOCK_HZ
	#define configSYSTICK_CLOCK_HZ configCPU_CLOCK_HZ//configSYSTICK_CLOCK_HZ=configCPU_CLOCK_HZ
	
	#define portNVIC_SYSTICK_CLK_BIT	( 1UL << 2UL )//无符号长整形32位二进制，左移两位
#else
	#define portNVIC_SYSTICK_CLK_BIT	( 0 )
#endif
#define portNVIC_SYSTICK_INT_BIT			( 1UL << 1UL )
#define portNVIC_SYSTICK_ENABLE_BIT			( 1UL << 0UL )
//初始化SysTick的函数如下
void vPortSetupTimerInterrupt( void )
{
     
    portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
    
    portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | 
                                  portNVIC_SYSTICK_INT_BIT |
                                  portNVIC_SYSTICK_ENABLE_BIT ); 
}

// port.c文件，SysTick中断服务函数
//里面调用了xTaskIncrementTick函数更新系统时基
void xPortSysTickHandler( void )
{
	
    vPortRaiseBASEPRI();
    
    xTaskIncrementTick();
	
    vPortClearBASEPRIFromISR();
}
//task.c文件，
static volatile TickType_t xTickCount 				= ( TickType_t ) 0U;
void xTaskIncrementTick( void )
{
    TCB_t *pxTCB = NULL;
    BaseType_t i = 0;
    
    const TickType_t xConstTickCount = xTickCount + 1;
    xTickCount = xConstTickCount;//把xTickCount加1
    
    
	for(i=0; i<configMAX_PRIORITIES; i++)
	{
        pxTCB = ( TCB_t * ) listGET_OWNER_OF_HEAD_ENTRY( ( &pxReadyTasksLists[i] ) );
		if(pxTCB->xTicksToDelay > 0)
		{
			pxTCB->xTicksToDelay --;
		}
	}
    
    portYIELD();
}