typedef struct tskTaskControlBlock
{
	volatile StackType_t * pxTopOfStack; //棧頂指針
	ListItem_t xStateListItem; //任務節(jié)點
	StackType_t * pxStack; //任務棧起始地址
	char pcTaskName[configMAX_TASK_NAME_LEN];//任務名稱
}tskTCB;

static void prvInitialiseNewTask(TaskFunction_t pxTaskCode,/*任務函數(shù)*/
                           const char * const pcName,/*任務名稱*/
						   const uint32_t ulStackDepth,/*任務棧大小，單位字*/
						   void * const pvParameters, /*任務形參*/
						   TaskHandle_t* const pxCreatedTask,/*任務句柄*/
						   TCB_t * pxNewTCB) /*任務控制塊指針*/
{
	StackType_t * pxTopOfStack;
	UBaseType_t x;
	//棧頂?shù)刂?
	pxTopOfStack = pxNewTCB->pxStack + (ulStackDepth - (uint32_t) 1);
	//項下做8字節(jié)對齊
	pxTopOfStack = (StackType_t*) (  (uint32_t)pxTopOfStack & (~(uint32_t)0x0007) );
	//存儲名字
	for(x=(UBaseType_t)0;x<(UBaseType_t)configMAX_TASK_NAME_LEN;x++)
	{
		pxNewTCB->pcTaskName[x] = pcName[x];
		if(pcName[x]=='\0')
			break;
	}
	pxNewTCB->pcTaskName[configMAX_TASK_NAME_LEN-1] = '\0';
	//初始化TCB中的xStateListItem列表項
	vListInitialiseItem(& (pxNewTCB->xStateListItem));
	//設置xStateListItem列表項的擁有者即為傳入的TCB
	listSET_LIST_ITEM_OWNER( &(pxNewTCB->xStateListItem), pxNewTCB );
	//初始化任務棧,并返回更新的棧頂指針
	pxNewTCB->pxTopOfStack = pxPortInitialiseStack(pxTopOfStack,pxTaskCode,pvParameters);
	//返回任務句柄
	if((void*)pxCreatedTask !=NULL )
	{
			*pxCreatedTask = (TaskHandle_t) pxNewTCB;
	}
}

#define portINITIAL_XPSR (0x01000000)
#define portSTART_ADDRESS_MASK ((StackType_t)0xfffffffeUL)
StackType_t * pxPortInitialiseStack(StackType_t* pxTopOfStack, TaskFunction_t pxCode, void*pvParameters)
{
    //-------------設置內(nèi)核會自動加載的寄存器，且順序不能變
	pxTopOfStack--;
	*pxTopOfStack = portINITIAL_XPSR;//xPSR bit24
	pxTopOfStack--;
	*pxTopOfStack = ( ( StackType_t ) pxCode ) & portSTART_ADDRESS_MASK;//R15 PC
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) prvTaskExitError;//R14 LR
	pxTopOfStack -= 5; //R12 R3 R2 R1 
	*pxTopOfStack = ( StackType_t ) pvParameters;//R0
	
	//--------------下面8個需要手動保存
	pxTopOfStack-=8;
	//返回更新后的棧頂指針
	return pxTopOfStack;
}

#define configMAX_PRIORITIES 5
List_t pxReadyTasksLists[configMAX_PRIORITIES];

void prvInitialiseTaskLists(void)
{
	UBaseType_t uxPriority;
	for(uxPriority = (UBaseType_t)0 ;
	    uxPriority < (UBaseType_t) configMAX_PRIORITIES;
	    uxPriority ++)
	{
			vListInitialise(&(pxReadyTasksLists[uxPriority]));
	}
}

void vTaskStartScheduler(void)
{
	//手動指定一個和要運行的任務
	pxCurrentTCB = &Task1TCB;
	//啟動調度器
	if(xPortStartScheduler()!=pdFALSE)
	{
		//啟動成功不會跑到這里
	}
}

//stm32 用4bit表示優(yōu)先級，所以最低優(yōu)先級則是15
#define configKERNEL_INTERRUPT_PRIORITY 15 
#define portNVIC_SYSPRI2_REG (*((volatile uint32_t*) 0xe000ed20))
#define portNVIC_PENDSV_PRI  (((uint32_t)configKERNEL_INTERRUPT_PRIORITY)<<16UL)
#define portNVIC_SYSTICK_PRI  (((uint32_t)configKERNEL_INTERRUPT_PRIORITY)<<24UL)
BaseType_t xPortStartScheduler(void)
{
	//把pendsv systick中斷優(yōu)先級設置為最低
	portNVIC_SYSPRI2_REG |=portNVIC_PENDSV_PRI;
	portNVIC_SYSPRI2_REG |=portNVIC_SYSTICK_PRI;
	
	//啟動第一個任務,該函數(shù)不會返回
	prvStartFirstTask();
	//不會運行到這里
	return 0;
}

__asm void prvStartFirstTask(void)
{
	PRESERVE8
	ldr r0, =0xE000ED08 //r0=0xE000ED08，相當于r0=&SCB_VTOR
	ldr r0, [r0]        //r0=*r0,即r0=*((uint32_t*)0xE000ED08),即r0=0x0
	ldr r0, [r0]        //r0=*r0,即r0=*((uint32_t*)0x0),即r0=msp指針值
	msr msp, r0         //msp=r0，msp指針獲得msp地址
	cpsie i   //開中斷
	cpsie f   //開中斷
	dsb
	isb
	svc 0    //觸發(fā)SVC系統(tǒng)調用，此后會進入SVCHandler
	nop      //下面這2個nop不會執(zhí)行
	nop
}

__asm void vPortSVCHandler(void)
{
	extern pxCurrentTCB;
	PRESERVE8
	//r3=&pxCurrentTCB,注意pxCurrentTCB本身就是一個指針，是指向一個任務的TCB指針
	ldr r3, =pxCurrentTCB  
	//r1=*r3，即r1=pxCurrentTCB
	ldr r1, [r3]           
	//r0=*r1，此時r1=pxCurrentTCB，
	//又結構體第一個成員（棧頂指針）的地址和結構體地址數(shù)值上是相同的，
	//所以r0=*(&(pxCurrentTCB.pxTopOfStack)),即r0=pxCurrentTCB.pxTopOfStack，
	//即r0此時指向當前任務空閑棧頂位置
	ldr r0, [r1]           
	//以r0為開始把r4-r11依次保存到當前任務的psp棧
	ldmia r0!,{r4-r11}
	//更新當前任務psp棧指針
	msr psp,r0
	isb
	mov r0, #0
	msr basepri,r0 //開中斷
    //此時r14是0xFFFF_FFF9，表示返回后進入Thread mode，使用MSP，返回Thmub狀態(tài)，
    //這里其實是把bit2置1，要求返回后使用PSP
	orr r14,#0x0d  
	//返回，這里會自動加載初始化任務棧填寫的xPSR、R15、R14、R12、R3-R0值到內(nèi)核對應寄存器，
	//所以返回后就直接到pxCurrentTCB指向的任務
	bx r14  
}

#define taskYIELD() portYIELD()

#define portNVIC_INT_CTRL_REG (*((volatile uint32_t*)0xe000ed04))
#define portNVIC_PENDSVSET_BIT (1<<28UL)
#define portSY_FULL_READ_WRITE (15)
#define portYIELD() \
{ \
   //觸發(fā)一次pendsv中斷
  	portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT; \
	  __dsb(portSY_FULL_READ_WRITE); \
	  __isb(portSY_FULL_READ_WRITE); \
}

__asm void xPortPendSVHandler(void)
{
    //進入中斷前會自動保存xPSR、R15、R14、R12、R3-R0到當前任務P棧中，此時任務棧頂指針指向要保存R11的位置
	extern pxCurrentTCB;
	extern vTaskSwitchContext;//這個函數(shù)是用來尋找下一個要運行的任務
	PRESERVE8
	mrs r0,psp  //當前任務棧psp指針存入r0，
	isb
	ldr r3,=pxCurrentTCB //r3=&pxCurrentTCB 
	ldr r2,[r3]          //r2=*r3, 即r2=pxCurrentTCB
	//以r0開始遞減的手動保存r4-r11
	stmdb r0!,{r4-r11}
	//r0=*r2，此時r2=pxCurrentTCB，
	//又結構體第一個成員（棧頂指針）的地址和結構體地址數(shù)值上是相同的，
	//所以r0=*(&(pxCurrentTCB.pxTopOfStack)),即r0=pxCurrentTCB.pxTopOfStack，
	//即r0此時指向當前任務空閑棧頂位置
	str r0,[r2]
	//到這里上文就保存完成
	//將r3、r14壓入棧保存起來（此時sp使用的是msp）
	//r14要保存是因為等下要調用函數(shù)，避免r14被覆蓋無法從pendsv中斷正常返回
	//r3要保存是因為r3保存的是當前正在運行任務控制塊的二級指針&pxCurrentTCB，后面要通過r3來操作pxCurrentTCB來切到下文
	stmdb sp!,{r3,r14}
	//關中斷，閾值是configMAX_SYSCALL_INTERRUPT_PRIORITY
	mov r0,#configMAX_SYSCALL_INTERRUPT_PRIORITY
	msr basepri,r0
	dsb
	isb
    //調用vTaskSwitchContext，功能是找到優(yōu)先級最高的任務，然后讓pxCurrentTCB = &優(yōu)先級最高任務TCB，我們這里手動指定
	bl vTaskSwitchContext
    //開中斷
	mov r0,#0
	msr basepri,r0
    //從msp中恢復r3、r14
	ldmia sp!,{r3,r14}
	//r1=*r3，此時r3=&pxCurrentTCB
	//即r1=pxCurrentTCB
	ldr r1,[r3] 
    //r0=*r1則r0=pxCurrentTCB.pxTopOfStack 理由前面講過
	ldr r0,[r1]
    //這里把pxCurrentTCB保存的需要手動加載的值加載到內(nèi)核的r4-r11
	ldmia r0!,{r4-r11}
    //更新加載了r4-r11的任務棧到psp
	msr psp,r0 
	isb
	//返回，這里會以psp自動加載保存了xPSR、R15、R14、R12、R3-R0值到內(nèi)核的xPSR、R15、R14、R12、R3-R0寄存器，所以返回的是pxCurrentTCB任務
	bx r14
	nop
}

extern TCB_t Task1TCB;
extern TCB_t Task2TCB;
void vTaskSwitchContext(void)
{
  if(pxCurrentTCB == &Task1TCB)
	{
		pxCurrentTCB = &Task2TCB;
	}
	else
	{
		pxCurrentTCB = &Task1TCB;
	}
}

extern List_t pxReadyTasksLists[configMAX_PRIORITIES];
portCHAR flag1;
portCHAR flag2;
TaskHandle_t Task1_Handle;
StackType_t Task1Stack[128];
TCB_t Task1TCB;
TaskHandle_t Task2_Handle;
StackType_t Task2Stack[128];
TCB_t Task2TCB;
void delay(uint32_t x)
{
	for(;x!=0;x--);
}
void Task1_Fntry(void *arg)
{
	while(1)
	{
	  flag1=1;
	  delay(100);
	  flag1=0;
	  delay(100);
      taskYIELD();//手動觸發(fā)切換任務
	}
}
void Task2_Fntry(void *arg)
{
	while(1)
	{
	 flag2=1;
	 delay(100);
	 flag2=0;
	 delay(100);
     taskYIELD();//手動觸發(fā)切換任務
	}
}
int main(void)
{
    //初始化就緒列表
    prvInitialiseTaskLists();
    //創(chuàng)建任務1
	Task1_Handle = xTaskCreateStatic(Task1_Fntry,"task1",128,NULL,Task1Stack,&Task1TCB);
	//將任務添加到就緒列表
	vListInsertEnd(&pxReadyTasksLists[1],&((&Task1TCB)->xStateListItem));
	//創(chuàng)建任務2
	Task2_Handle = xTaskCreateStatic(Task2_Fntry,"task2",128,NULL,Task2Stack,&Task2TCB);
	//將任務添加到就緒列表
	vListInsertEnd(&pxReadyTasksLists[2],&((&Task2TCB)->xStateListItem));
	//啟動調度器
	vTaskStartScheduler();
	for(;;);
}