Chapter 4 - 中断与时间管理
Created by : Mr Dk.
2019 / 11 / 19 21:59
Nanjing, Jiangsu, China
4.1 中断相关概念
4.1.1 中断
中断定义为 CPU 对系统内外发生的异步时间的响应。异步事件：没有时序关系，随机发生的事件。CPU 接到请求后，中止当前工作，保存当前运行环境，转去处理响应的异步事件任务。在中断服务期间，CPU 允许中断嵌套。
4.1.2 中断延迟时间
硬件中断发生，到 CPU 开始处理中断（保存 CPU 现场）的时间，是实时内核最重要的指标，通常由关中断的时间决定——关中断的时间越长，中断延迟就越长。
4.1.3 中断响应时间
中断响应时间 = 中断延迟 + 保存 CPU 内部寄存器的时间 + 内核进入中断服务函数的时间
4.1.4 中断恢复时间
恢复 CPU 内部寄存器 + 执行中断返回指令的时间
4.1.6 非屏蔽中断
不能用系统指令关闭的中断
- 优先级高
- 延迟时间短
- 响应快
- 不能被嵌套
- 不能忍受内核的延迟
用于紧急事件处理。
4.2 μC/OS-II 的中断处理
4.2.1 中断处理程序
μC/OS-II 需要知道当前内核是否正在处理中断，所以在中断服务子程序中，要调用两个函数，通知内核进入或退出中断。这两个函数对 中断嵌套层数计数器 OSIntNesting 进行维护。而 OS 也是通过这个计数器来判断当前内核是否处在中断或嵌套中断中。这个计数器是一个 单字节 的整型全局变量，因此嵌套层数最多为 255
下面是 OSIntEnter() 函数：
- 进入中断处理程序时被调用
- 对计数器 +1
/*
*********************************************************************************************************
* ENTER ISR
*
* Description: This function is used to notify uC/OS-II that you are about to service an interrupt
* service routine (ISR). This allows uC/OS-II to keep track of interrupt nesting and thus
* only perform rescheduling at the last nested ISR.
*
* Arguments : none
*
* Returns : none
*
* Notes : 1) This function should be called ith interrupts already disabled
* 2) Your ISR can directly increment OSIntNesting without calling this function because
* OSIntNesting has been declared 'global'.
* 3) You MUST still call OSIntExit() even though you increment OSIntNesting directly.
* 4) You MUST invoke OSIntEnter() and OSIntExit() in pair. In other words, for every call
* to OSIntEnter() at the beginning of the ISR you MUST have a call to OSIntExit() at the
* end of the ISR.
* 5) You are allowed to nest interrupts up to 255 levels deep.
* 6) I removed the OS_ENTER_CRITICAL() and OS_EXIT_CRITICAL() around the increment because
* OSIntEnter() is always called with interrupts disabled.
*********************************************************************************************************
*/
void OSIntEnter (void)
{
if (OSRunning == OS_TRUE) {
if (OSIntNesting < 255u) {
OSIntNesting++; /* Increment ISR nesting level */
}
}
}
下面是 OSIntExit() 函数：
- 退出中断处理程序时被调用
- 计数器 -1
- 找出就绪的最高优先级任务
- 判断最高优先级任务是否是被中断打断的任务，如果不是，则切换 TCB 指针
- 调用 中断级任务切换函数
OSIntCtxSw()进行任务切换
注意，任务切换的条件是：中断嵌套计数器和调度锁定嵌套计数器同时为 0。
/*
*********************************************************************************************************
* EXIT ISR
*
* Description: This function is used to notify uC/OS-II that you have completed serviving an ISR. When
* the last nested ISR has completed, uC/OS-II will call the scheduler to determine whether
* a new, high-priority task, is ready to run.
*
* Arguments : none
*
* Returns : none
*
* Notes : 1) You MUST invoke OSIntEnter() and OSIntExit() in pair. In other words, for every call
* to OSIntEnter() at the beginning of the ISR you MUST have a call to OSIntExit() at the
* end of the ISR.
* 2) Rescheduling is prevented when the scheduler is locked (see OS_SchedLock())
*********************************************************************************************************
*/
void OSIntExit (void)
{
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
if (OSRunning == OS_TRUE) {
OS_ENTER_CRITICAL();
if (OSIntNesting > 0u) { /* Prevent OSIntNesting from wrapping */
OSIntNesting--;
}
if (OSIntNesting == 0u) { /* Reschedule only if all ISRs complete ... */
if (OSLockNesting == 0u) { /* ... and not locked. */
OS_SchedNew();
OSTCBHighRdy = OSTCBPrioTbl[OSPrioHighRdy];
if (OSPrioHighRdy != OSPrioCur) { /* No Ctx Sw if current task is highest rdy */
#if OS_TASK_PROFILE_EN > 0u
OSTCBHighRdy->OSTCBCtxSwCtr++; /* Inc. # of context switches to this task */
#endif
OSCtxSwCtr++; /* Keep track of the number of ctx switches */
OSIntCtxSw(); /* Perform interrupt level ctx switch */
}
}
}
OS_EXIT_CRITICAL();
}
}
4.3 μC/OS-II 的时钟节拍
4.3.1 时钟节拍
时钟节拍是特定的周期性中断（时钟中断），是系统心脏的脉动。
4.3.2 时钟节拍程序
时钟节拍中断服务子程序 OSTickISR()：每个时钟周期执行一次，必须用汇编实现。
节拍服务子函数 OSTImeTick() - 由上一个函数调用：
- 给每个 TCB 的延迟项
OSTCBDly减 1 直至为 0 - 执行时间与任务个数成正比
/*
*********************************************************************************************************
* 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 > 0u
BOOLEAN step;
#endif
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#if OS_TIME_TICK_HOOK_EN > 0u
OSTimeTickHook(); /* Call user definable hook */
#endif
#if OS_TIME_GET_SET_EN > 0u
OS_ENTER_CRITICAL(); /* Update the 32-bit tick counter */
OSTime++;
OS_EXIT_CRITICAL();
#endif
if (OSRunning == OS_TRUE) {
#if OS_TICK_STEP_EN > 0u
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 */
OS_ENTER_CRITICAL();
if (ptcb->OSTCBDly != 0u) { /* No, Delayed or waiting for event with TO */
ptcb->OSTCBDly--; /* Decrement nbr of ticks to end of delay */
if (ptcb->OSTCBDly == 0u) { /* Check for timeout */
if ((ptcb->OSTCBStat & OS_STAT_PEND_ANY) != OS_STAT_RDY) {
ptcb->OSTCBStat &= (INT8U)~(INT8U)OS_STAT_PEND_ANY; /* Yes, Clear status flag */
ptcb->OSTCBStatPend = OS_STAT_PEND_TO; /* Indicate PEND timeout */
} else {
ptcb->OSTCBStatPend = OS_STAT_PEND_OK;
}
if ((ptcb->OSTCBStat & OS_STAT_SUSPEND) == OS_STAT_RDY) { /* Is task suspended? */
OSRdyGrp |= ptcb->OSTCBBitY; /* No, Make ready */
OSRdyTbl[ptcb->OSTCBY] |= ptcb->OSTCBBitX;
}
}
}
ptcb = ptcb->OSTCBNext; /* Point at next TCB in TCB list */
OS_EXIT_CRITICAL();
}
}
}
4.3.3 时钟节拍器的正确用法
多任务启动后再开放时钟中断，防止时钟中断在 OS 启动第一个任务前发生。
4.4 μC/OS-II 的时间管理
4.4.1 任务延时函数 - OSTimeDly() 函数
除了永不挂起的空闲任务外，其它任务总该在合适的时候调用系统服务函数，自我挂起。暂时放弃 CPU 使用权，使得低优先级的任务得以运行。该函数向 OS 申请延时，申请以时钟节拍为单位。当：
- 延时时间到
- 其它任务调用
OSTimeDlyResume()取消了延时
任务才会重新进入就绪状态。当然，被不被调度取决于任务的优先级。
原理：
- 将任务从就绪表中移出
- 在 TCB 中记录延时时间，由时钟中断递减该时间
/*
*********************************************************************************************************
* DELAY TASK 'n' TICKS
*
* Description: This function is called to delay execution of the currently running task until the
* specified number of system ticks expires. This, of course, directly equates to delaying
* the current task for some time to expire. No delay will result If the specified delay is
* 0. If the specified delay is greater than 0 then, a context switch will result.
*
* Arguments : ticks is the time delay that the task will be suspended in number of clock 'ticks'.
* Note that by specifying 0, the task will not be delayed.
*
* Returns : none
*********************************************************************************************************
*/
void OSTimeDly (INT32U ticks)
{
INT8U y;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
if (OSIntNesting > 0u) { /* See if trying to call from an ISR */
return;
}
if (OSLockNesting > 0u) { /* See if called with scheduler locked */
return;
}
if (ticks > 0u) { /* 0 means no delay! */
OS_ENTER_CRITICAL();
y = OSTCBCur->OSTCBY; /* Delay current task */
OSRdyTbl[y] &= (OS_PRIO)~OSTCBCur->OSTCBBitX;
if (OSRdyTbl[y] == 0u) {
OSRdyGrp &= (OS_PRIO)~OSTCBCur->OSTCBBitY;
}
OSTCBCur->OSTCBDly = ticks; /* Load ticks in TCB */
OS_EXIT_CRITICAL();
OS_Sched(); /* Find next task to run! */
}
}
4.4.2 按时分秒毫秒延时函数 - OSTimeDlyHMSM() 函数
按时间单位为单位进行延时，显然需要将延时参数换算成时钟节拍数量，记录在 TCB 中。所以需要利用全局常量 OS_TICKS_PER_SEC 将时间转换为节拍数。这个常量的含义：每秒产生多少个节拍。
/*
*********************************************************************************************************
* DELAY TASK FOR SPECIFIED TIME
*
* Description: This function is called to delay execution of the currently running task until some time
* expires. This call allows you to specify the delay time in HOURS, MINUTES, SECONDS and
* MILLISECONDS instead of ticks.
*
* Arguments : hours specifies the number of hours that the task will be delayed (max. is 255)
* minutes specifies the number of minutes (max. 59)
* seconds specifies the number of seconds (max. 59)
* ms specifies the number of milliseconds (max. 999)
*
* Returns : OS_ERR_NONE
* OS_ERR_TIME_INVALID_MINUTES
* OS_ERR_TIME_INVALID_SECONDS
* OS_ERR_TIME_INVALID_MS
* OS_ERR_TIME_ZERO_DLY
* OS_ERR_TIME_DLY_ISR
*
* Note(s) : The resolution on the milliseconds depends on the tick rate. For example, you can't do
* a 10 mS delay if the ticker interrupts every 100 mS. In this case, the delay would be
* set to 0. The actual delay is rounded to the nearest tick.
*********************************************************************************************************
*/
#if OS_TIME_DLY_HMSM_EN > 0u
INT8U OSTimeDlyHMSM (INT8U hours,
INT8U minutes,
INT8U seconds,
INT16U ms)
{
INT32U ticks;
if (OSIntNesting > 0u) { /* See if trying to call from an ISR */
return (OS_ERR_TIME_DLY_ISR);
}
if (OSLockNesting > 0u) { /* See if called with scheduler locked */
return (OS_ERR_SCHED_LOCKED);
}
#if OS_ARG_CHK_EN > 0u
if (hours == 0u) {
if (minutes == 0u) {
if (seconds == 0u) {
if (ms == 0u) {
return (OS_ERR_TIME_ZERO_DLY);
}
}
}
}
if (minutes > 59u) {
return (OS_ERR_TIME_INVALID_MINUTES); /* Validate arguments to be within range */
}
if (seconds > 59u) {
return (OS_ERR_TIME_INVALID_SECONDS);
}
if (ms > 999u) {
return (OS_ERR_TIME_INVALID_MS);
}
#endif
/* Compute the total number of clock ticks required.. */
/* .. (rounded to the nearest tick) */
ticks = ((INT32U)hours * 3600uL + (INT32U)minutes * 60uL + (INT32U)seconds) * OS_TICKS_PER_SEC
+ OS_TICKS_PER_SEC * ((INT32U)ms + 500uL / OS_TICKS_PER_SEC) / 1000uL;
OSTimeDly(ticks);
return (OS_ERR_NONE);
}
#endif
4.4.3 结束任务延时 - OSTimeDlyResume() 函数
唤醒一个用上面两个延时函数挂起的任务，取消延时，使其进入就绪状态
原理：
- 将 TCB 中的
OSTCBDly直接清 0 - 将任务插入到就绪表中，如果有需要的话，需要重新调度
- 不使用延时挂起函数挂起的任务不能用这个函数唤醒
/*
*********************************************************************************************************
* RESUME A DELAYED TASK
*
* Description: This function is used resume a task that has been delayed through a call to either
* OSTimeDly() or OSTimeDlyHMSM(). Note that you can call this function to resume a
* task that is waiting for an event with timeout. This would make the task look
* like a timeout occurred.
*
* Arguments : prio specifies the priority of the task to resume
*
* Returns : OS_ERR_NONE Task has been resumed
* OS_ERR_PRIO_INVALID if the priority you specify is higher that the maximum allowed
* (i.e. >= OS_LOWEST_PRIO)
* OS_ERR_TIME_NOT_DLY Task is not waiting for time to expire
* OS_ERR_TASK_NOT_EXIST The desired task has not been created or has been assigned to a Mutex.
*********************************************************************************************************
*/
#if OS_TIME_DLY_RESUME_EN > 0u
INT8U OSTimeDlyResume (INT8U prio)
{
OS_TCB *ptcb;
#if OS_CRITICAL_METHOD == 3u /* Storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
if (prio >= OS_LOWEST_PRIO) {
return (OS_ERR_PRIO_INVALID);
}
OS_ENTER_CRITICAL();
ptcb = OSTCBPrioTbl[prio]; /* Make sure that task exist */
if (ptcb == (OS_TCB *)0) {
OS_EXIT_CRITICAL();
return (OS_ERR_TASK_NOT_EXIST); /* The task does not exist */
}
if (ptcb == OS_TCB_RESERVED) {
OS_EXIT_CRITICAL();
return (OS_ERR_TASK_NOT_EXIST); /* The task does not exist */
}
if (ptcb->OSTCBDly == 0u) { /* See if task is delayed */
OS_EXIT_CRITICAL();
return (OS_ERR_TIME_NOT_DLY); /* Indicate that task was not delayed */
}
ptcb->OSTCBDly = 0u; /* Clear the time delay */
if ((ptcb->OSTCBStat & OS_STAT_PEND_ANY) != OS_STAT_RDY) {
ptcb->OSTCBStat &= ~OS_STAT_PEND_ANY; /* Yes, Clear status flag */
ptcb->OSTCBStatPend = OS_STAT_PEND_TO; /* Indicate PEND timeout */
} else {
ptcb->OSTCBStatPend = OS_STAT_PEND_OK;
}
if ((ptcb->OSTCBStat & OS_STAT_SUSPEND) == OS_STAT_RDY) { /* Is task suspended? */
OSRdyGrp |= ptcb->OSTCBBitY; /* No, Make ready */
OSRdyTbl[ptcb->OSTCBY] |= ptcb->OSTCBBitX;
OS_EXIT_CRITICAL();
OS_Sched(); /* See if this is new highest priority */
} else {
OS_EXIT_CRITICAL(); /* Task may be suspended */
}
return (OS_ERR_NONE);
}
#endif
4.4.4 系统时间函数 - OSTimeGet() 和 OSTimeSet()
时钟节拍每发生一次，OS 就会给一个 32-bit 计数器 OSTime + 1。这两个函数分别 get 或 set 这个计数器。这个全局变量是 32-bit 的，因此在 8-bit 的 CPU 上操作需要多条指令，这些指令需要一次执行完毕——因此需要在临界区中！
/*
*********************************************************************************************************
* GET CURRENT SYSTEM TIME
*
* Description: This function is used by your application to obtain the current value of the 32-bit
* counter which keeps track of the number of clock ticks.
*
* Arguments : none
*
* Returns : The current value of OSTime
*********************************************************************************************************
*/
#if OS_TIME_GET_SET_EN > 0u
INT32U OSTimeGet (void)
{
INT32U ticks;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
OS_ENTER_CRITICAL();
ticks = OSTime;
OS_EXIT_CRITICAL();
return (ticks);
}
#endif
/*
*********************************************************************************************************
* SET SYSTEM CLOCK
*
* Description: This function sets the 32-bit counter which keeps track of the number of clock ticks.
*
* Arguments : ticks specifies the new value that OSTime needs to take.
*
* Returns : none
*********************************************************************************************************
*/
#if OS_TIME_GET_SET_EN > 0u
void OSTimeSet (INT32U ticks)
{
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
OS_ENTER_CRITICAL();
OSTime = ticks;
OS_EXIT_CRITICAL();
}
#endif