vTaskStartScheduler
创建空闲进程， 调用适配xPortStartScheduler();

void vTaskStartScheduler( void )
{xReturn = xTaskCreate( prvIdleTask,configIDLE_TASK_NAME,configMINIMAL_STACK_SIZE,( void * ) NULL,portPRIVILEGE_BIT,&xIdleTaskHandle );if( xReturn == pdPASS ){portDISABLE_INTERRUPTS();xNextTaskUnblockTime = portMAX_DELAY;xSchedulerRunning = pdTRUE;xTickCount = ( TickType_t ) configINITIAL_TICK_COUNT;xPortStartScheduler();}else{configASSERT( xReturn != errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY );}
}

stm32，适配不同有差异

设置挂起中断和系统定时中断优先级，设置定时中断

BaseType_t xPortStartScheduler( void )                                                                                                             
{portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;   //pendsv 优先级portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;  // systick 优先级vPortSetupTimerInterrupt();uxCriticalNesting = 0;prvPortStartFirstTask();vTaskSwitchContext();prvTaskExitError();return 0;
}

设置系统定时中断

__attribute__( ( weak ) ) void vPortSetupTimerInterrupt( void )                                                                                    
{portNVIC_SYSTICK_CTRL_REG = 0UL;portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT_CONFIG | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );
}

portNVIC_SYSTICK_LOAD_REG 系统定时计数器重载时间
portNVIC_SYSTICK_CTRL_REG

[2]CLKSOURCE 1 = core clock.
[1]TICKINT 1 = counting down to 0 pends the SysTick handler.
[0]ENABLE 1

prvPortStartFirstTask，调用svc中断

static void prvPortStartFirstTask( void )                                                                                                          
{__asm volatile (" ldr r0, =0xE000ED08   \n"  " ldr r0, [r0]          \n"                //中断向量表偏移" ldr r0, [r0]          \n"				// 取出中断向量表第一个数据 即栈顶指针" msr msp, r0           \n"			//设置msp指向栈顶" cpsie i               \n"					// 开中断" cpsie f               \n"					//开异常" dsb                   \n"					//数据同步屏障" isb                   \n"						//清空流水线" svc 0                 \n"					//svc中断" nop                   \n"" .ltorg                \n"   			// 数据缓冲池);
}

恢复任务context

void vPortSVCHandler( void )
{__asm volatile ("   ldr r3, pxCurrentTCBConst2      \n"     //当前任务块"   ldr r1, [r3]                    \n"							"   ldr r0, [r1]                    \n"						 //第一个数据为任务块栈顶指针"   ldmia r0!, {r4-r11}             \n" 			 	// 恢复r4-r11"   msr psp, r0                     \n"					//恢复栈"   isb                             \n"                              //清空流水线                                                                      "   mov r0, #0                      \n"					"   msr basepri, r0                 \n""   orr r14, #0xd                   \n""   bx r14                          \n"					//从中断返回"                                   \n""   .align 4                        \n""pxCurrentTCBConst2: .word pxCurrentTCB             \n");
}

就绪链表查找最高优先级，赋值给当前任务

void vTaskSwitchContext( void )
{if( uxSchedulerSuspended != ( UBaseType_t ) pdFALSE ){xYieldPending = pdTRUE;}else{xYieldPending = pdFALSE;taskSELECT_HIGHEST_PRIORITY_TASK();}
}

#define taskSELECT_HIGHEST_PRIORITY_TASK()                                \
{                                                                         \UBaseType_t uxTopPriority = uxTopReadyPriority;                       \\\while( listLIST_IS_EMPTY( &( pxReadyTasksLists[ uxTopPriority ] ) ) ) \{                                                                     \configASSERT( uxTopPriority );                                    \--uxTopPriority;                                                  \}                                                                     \\\listGET_OWNER_OF_NEXT_ENTRY( pxCurrentTCB, &( pxReadyTasksLists[ uxTopPriority ] ) ); \uxTopReadyPriority = uxTopPriority;                                                   \
}