UC/OS-II基礎知識之時間管理
由於嵌入式系統的任務是一個無限循環,並且UC/OS-II還是個搶佔式內核,所以爲了使優先級別高的任務不至於獨佔CPU,UC/OS-II規定:除了空閒任務之外的所有任務必須在任務中合適的位置調用系統提供的函數OSTimeDly(),使當前任務的運行延時(暫停)一段時間並進行一次任務調度,以讓出CPU的使用權。
函數OSTimeDly()的代碼如下
void OSTimeDly (INT16U ticks)
{
INT8U y;
#if OS_CRITICAL_METHOD == 3 /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0;
#endif
if (ticks > 0) { /* 0 means no delay! */
OS_ENTER_CRITICAL();
y = OSTCBCur->OSTCBY; /* Delay current task */
OSRdyTbl[y] &= ~OSTCBCur->OSTCBBitX;
if (OSRdyTbl[y] == 0) {
OSRdyGrp &= ~OSTCBCur->OSTCBBitY;
}
OSTCBCur->OSTCBDly = ticks; /* Load ticks in TCB */
OS_EXIT_CRITICAL();
OS_Sched(); /* Find next task to run! */
}
}
函數的參數ticks是一時鐘節拍數爲單位的延時時間。爲了使用更爲習慣的方法來使任務延時,系統還提供了用時,分,秒,微妙爲參數的延時任務OSTimeDlyHMSM(),其函數原型如下:
#if OS_TIME_DLY_HMSM_EN > 0
INT8U OSTimeDlyHMSM (INT8U hours, INT8U minutes, INT8U seconds, INT16U milli)
{
INT32U ticks;
INT16U loops;
#if OS_ARG_CHK_EN > 0
if (hours == 0) {
if (minutes == 0) {
if (seconds == 0) {
if (milli == 0) {
return (OS_TIME_ZERO_DLY);
}
}
}
}
if (minutes > 59) {
return (OS_TIME_INVALID_MINUTES); /* Validate arguments to be within range */
}
if (seconds > 59) {
return (OS_TIME_INVALID_SECONDS);
}
if (milli > 999) {
return (OS_TIME_INVALID_MILLI);
}
#endif
/* Compute the total number of clock ticks required.. */
/* .. (rounded to the nearest tick) */
ticks = ((INT32U)hours * 3600L + (INT32U)minutes * 60L + (INT32U)seconds) * OS_TICKS_PER_SEC
+ OS_TICKS_PER_SEC * ((INT32U)milli + 500L / OS_TICKS_PER_SEC) / 1000L;
loops = (INT16U)(ticks / 65536L); /* Compute the integral number of 65536 tick delays */
ticks = ticks % 65536L; /* Obtain the fractional number of ticks */
OSTimeDly((INT16U)ticks);
while (loops > 0) {
OSTimeDly((INT16U)32768u);
OSTimeDly((INT16U)32768u);
loops--;
}
return (OS_NO_ERR);
}
調用延時函數,當規定的延時時間期滿,或者有其他任務通過調用函數OSTimeDlyResume()取消延時時,他會立即進入就緒狀態。如果任務比正在運行的任務優先級別高,則立即引發一次任務調度。