ucos实时系统--不支持时间片轮训版本 SysTick 配置分析
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目的：看看ucos中SysTick的中断优先级配置情况。
关于 SysTick 定时器的 说明参见我的另一个文章。--STM32F10XXXX---SysTick滴答定时器
在系统启动多任务后的第一个任务TaskStart中（即调用过OSStart()函数后），
先初始化BSP(Board Support Package)板级支持包：
- 设定RCC(复位和实时时钟控制)外设，对系统时钟源进行设置
- 初始化系统驱动程序；
然后调用OS_CPU_SysTickInit()完成对系统Tick的设定。
先上程序：
os_cpu_c.c中的相关宏定义
/*********************************************************************************************************** SYS TICK DEFINES**********************************************************************************************************/#define OS_CPU_CM3_NVIC_ST_CTRL (*((volatile INT32U *)0xE000E010)) /* SysTick Ctrl & Status Reg. */#define OS_CPU_CM3_NVIC_ST_RELOAD (*((volatile INT32U *)0xE000E014)) /* SysTick Reload Value Reg. */#define OS_CPU_CM3_NVIC_ST_CURRENT (*((volatile INT32U *)0xE000E018)) /* SysTick Current Value Reg. */#define OS_CPU_CM3_NVIC_ST_CAL (*((volatile INT32U *)0xE000E01C)) /* SysTick Cal Value Reg. *///SysTick校准值寄存器#define OS_CPU_CM3_NVIC_ST_CTRL_COUNT 0x00010000 /* Count flag. */#define OS_CPU_CM3_NVIC_ST_CTRL_CLK_SRC 0x00000004 /* Clock Source. */#define OS_CPU_CM3_NVIC_ST_CTRL_INTEN 0x00000002 /* Interrupt enable. */#define OS_CPU_CM3_NVIC_ST_CTRL_ENABLE 0x00000001 /* Counter mode. */
/*********************************************************************************************************** OS_CPU_SysTickInit()** Description: Initialize the SysTick.** Arguments : none.** Note(s) : 1) This function MUST be called after OSStart() & after processor initialization.**********************************************************************************************************/void OS_CPU_SysTickInit (void){ INT32U cnts; //通过已经设置的RCC_ClocksTypeDef的HCLK_Frequency时钟频率 如：72M cnts = OS_CPU_SysTickClkFreq() / OS_TICKS_PER_SEC; //<span style="font-family: Arial, Helvetica, sans-serif;">OS_TICKS_PER_SEC设置为1000</span> OS_CPU_CM3_NVIC_ST_RELOAD = (cnts - 1); //得到的值写入 Systick 重装载数值寄存器 /* Enable timer. */ OS_CPU_CM3_NVIC_ST_CTRL |= OS_CPU_CM3_NVIC_ST_CTRL_CLK_SRC | OS_CPU_CM3_NVIC_ST_CTRL_ENABLE; /* Enable timer interrupt. */ OS_CPU_CM3_NVIC_ST_CTRL |= OS_CPU_CM3_NVIC_ST_CTRL_INTEN;}上边的SysTick外设的宏定义中的注释可能有错误：
OS_CPU_CM3_NVIC_ST_CTRL_INTEN ：SysTick一定是向下计数的模式，该位决定----当事件到来时，是否发出异常请求。
OS_CPU_CM3_NVIC_ST_CTRL_ENABLE：定时器使能。
OS_CPU_SysTickInit实现功能：
- SysTick自动重装载值寄存器 填充；
- SysTick控制状态寄存器设置：选择内核时钟(FCLK)、定时器使能、事件到达触发异常
SysTick异常处理程序：
/*********************************************************************************************************** OS_CPU_SysTickHandler()** Description: Handle the system tick (SysTick) interrupt, which is used to generate the uC/OS-II tick* interrupt.** Arguments : none.** Note(s) : 1) This function MUST be placed on entry 15 of the Cortex-M3 vector table.**********************************************************************************************************/void OS_CPU_SysTickHandler (void){ OS_CPU_SR cpu_sr; OS_ENTER_CRITICAL(); /* Tell uC/OS-II that we are starting an ISR */ OSIntNesting++; OS_EXIT_CRITICAL(); OSTimeTick(); /* Call uC/OS-II's OSTimeTick() */ OSIntExit(); /* Tell uC/OS-II that we are leaving the ISR */}先OSIntNesting++;Tell uC/OS-II我们正在开始一个ISR终端服务程序。
后OSTimeTick(); 目的是在时钟节拍到来时，检查每个任务的任务控制块中的.OSTCBDly-1后是否为0，如果是，那么表明这个任务刚才是挂起的状态，此时应改变为就绪态
最后是OSIntExit(); ---OS_SchedNew();调度发生
说说OSTimeTick();
任务状态图如下：
先弄几个宏定义
OS_EXT BOOLEAN OSRunning; /* Flag indicating that kernel is running */
#if OS_TICK_STEP_EN > 0OS_EXT INT8U OSTickStepState; /* Indicates the state of the tick step feature */#endif
/*********************************************************************************************************** Values for OSTickStepState** Note(s): This feature is used by uC/OS-View.**********************************************************************************************************/#if OS_TICK_STEP_EN > 0#define OS_TICK_STEP_DIS 0u /* Stepping is disabled, tick runs as mormal */#define OS_TICK_STEP_WAIT 1u /* Waiting for uC/OS-View to set OSTickStepState to _ONCE */#define OS_TICK_STEP_ONCE 2u /* Process tick once and wait for next cmd from uC/OS-View */#endif
#define OS_TASK_IDLE_PRIO (OS_LOWEST_PRIO) /* IDLE task priority
/*********************************************************************************************************** TASK STATUS (Bit definition for OSTCBStat)**********************************************************************************************************/#define OS_STAT_RDY 0x00u /* Ready to run */#define OS_STAT_SEM 0x01u /* Pending on semaphore */#define OS_STAT_MBOX 0x02u /* Pending on mailbox */#define OS_STAT_Q 0x04u /* Pending on queue */#define OS_STAT_SUSPEND 0x08u /* Task is suspended */#define OS_STAT_MUTEX 0x10u /* Pending on mutual exclusion semaphore */#define OS_STAT_FLAG 0x20u /* Pending on event flag group */#define OS_STAT_MULTI 0x80u /* Pending on multiple events */#define OS_STAT_PEND_ANY (OS_STAT_SEM | OS_STAT_MBOX | OS_STAT_Q | OS_STAT_MUTEX | OS_STAT_FLAG)
/*********************************************************************************************************** TASK PEND STATUS (Status codes for OSTCBStatPend)**********************************************************************************************************/#define OS_STAT_PEND_OK 0u /* Pending status OK, not pending, or pending complete */#define OS_STAT_PEND_TO 1u /* Pending timed out */#define OS_STAT_PEND_ABORT 2u /* Pending aborted */
OSTimeTick();
/*********************************************************************************************************** PROCESS SYSTEM TICK** Description: This function is used to signal to uC/OS-II the occurrence of a 'system tick' (also known* as a 'clock tick'). This function should be called by the ticker ISR but, can also be* called by a high priority task.** Arguments : none** Returns : none**********************************************************************************************************/void OSTimeTick (void){ OS_TCB *ptcb;#if OS_TICK_STEP_EN > 0 BOOLEAN step;#endif#if OS_CRITICAL_METHOD == 3 /* Allocate storage for CPU status register */ OS_CPU_SR cpu_sr = 0;#endif#if OS_TIME_TICK_HOOK_EN > 0 OSTimeTickHook(); /* Call user definable hook */#endif#if OS_TIME_GET_SET_EN > 0 OS_ENTER_CRITICAL(); /* Update the 32-bit tick counter */ OSTime++; OS_EXIT_CRITICAL();#endif if (OSRunning == OS_TRUE) {#if OS_TICK_STEP_EN > 0 switch (OSTickStepState) { /* Determine whether we need to process a tick */ case OS_TICK_STEP_DIS: /* Yes, stepping is disabled */ step = OS_TRUE; break; case OS_TICK_STEP_WAIT: /* No, waiting for uC/OS-View to set ... */ step = OS_FALSE; /* .. OSTickStepState to OS_TICK_STEP_ONCE */ break; case OS_TICK_STEP_ONCE: /* Yes, process tick once and wait for next ... */ step = OS_TRUE; /* ... step command from uC/OS-View */ OSTickStepState = OS_TICK_STEP_WAIT; break; default: /* Invalid case, correct situation */ step = OS_TRUE; OSTickStepState = OS_TICK_STEP_DIS; break; } if (step == OS_FALSE) { /* Return if waiting for step command */ return; }#endif ptcb = OSTCBList; /* Point at first TCB in TCB list */ while (ptcb->OSTCBPrio != OS_TASK_IDLE_PRIO) { /* Go through all TCBs in TCB list//遍历 */ OS_ENTER_CRITICAL(); if (ptcb->OSTCBDly != 0) { /* No, Delayed or waiting for event with TO */ if (--ptcb->OSTCBDly == 0) { /* Decrement nbr of ticks to end of delay */ /* Check for timeout */ if ((ptcb->OSTCBStat & OS_STAT_PEND_ANY) != OS_STAT_RDY) {//不为就绪态，置成就绪态 ptcb->OSTCBStat &= ~(INT8U)OS_STAT_PEND_ANY; /* Yes, Clear status flag 就绪态OS_STAT_RDY */ ptcb->OSTCBStatPend = OS_STAT_PEND_TO; /* Indicate PEND timeout 挂起状态设置为挂起超时<span style="font-family: Arial, Helvetica, sans-serif;">OS_STAT_PEND_TO</span> */ } else { ptcb->OSTCBStatPend = OS_STAT_PEND_OK;//否则挂起状态OK } if ((ptcb->OSTCBStat & OS_STAT_SUSPEND) == OS_STAT_RDY) { /* Is task suspended? 任务暂停？ */ OSRdyGrp |= ptcb->OSTCBBitY; /* No, Make ready 不是暂停，将它就绪 */ OSRdyTbl[ptcb->OSTCBY] |= ptcb->OSTCBBitX; } } } ptcb = ptcb->OSTCBNext; /* Point at next TCB in TCB list */ OS_EXIT_CRITICAL(); } }}OSIntExit();
---待续，,,,
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