一.Preface
理解Freertos的任务调度对理解整个实时操作系统是非常有帮助的，最近抽空又复习了一遍源码，所以在此记录一下。
二.freertos的3各任务链表
2.1ready list(array)
a.这是一个链表组，定义了最高优先级为10，则有10个readylist。
b.每隔1个tick，freertos的tick中断就会从里面寻找最高优先级的task链表依次切换，并执行。
2.2delayed list
a.在任务中使用vTaskDelay(or vTaskDelayUntil)会把当前任务放入delayed list。
b.每隔1个tick，freertos的tick中断就会去判断delayed list中任务阻塞时间，如果时间到了，则将任务加入到对应优先级的ready list。
2.3pending list
b.pengding list的用法
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vTaskSuspendAll(); /*确保同一时刻把数据放入队列中*/xQueueOverwrite(accelerometerDataQueue, &sensors.acc);xQueueOverwrite(gyroDataQueue, &sensors.gyro);if (isMagPresent){xQueueOverwrite(magnetometerDataQueue, &sensors.mag);}if (isBaroPresent){xQueueOverwrite(barometerDataQueue, &sensors.baro);}xTaskResumeAll();
2.4对应的链表代码
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PRIVILEGED_DATA static List_t pxReadyTasksLists[ configMAX_PRIORITIES ];/*< Prioritised ready tasks. */
PRIVILEGED_DATA static List_t xDelayedTaskList1; /*< Delayed tasks. */
PRIVILEGED_DATA static List_t xDelayedTaskList2; /*< Delayed tasks (two lists are used - one for delays that have overflowed the current tick count. */
PRIVILEGED_DATA static List_t * volatile pxDelayedTaskList; /*< Points to the delayed task list currently being used. */
PRIVILEGED_DATA static List_t * volatile pxOverflowDelayedTaskList; /*< Points to the delayed task list currently being used to hold tasks that have overflowed the current tick count. */
PRIVILEGED_DATA static List_t xPendingReadyList; /*<