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使用sys/bios定时器时，定时器周期如何计算

user4431315
Prodigy 100 points
Other Parts Discussed in Thread: SYSBIOS, TDA4VM

你好：

    最近我在使用sys/bios定时器时，发现实际定时器周期与我代码设置周期值不一致，我想文下如何计算这个值？代码如下：

Error_Block eb;
Timer_Params timerParams;

Error_init(&eb);

/* Initialize the timer params */
Timer_Params_init(&timerParams);
timerParams.extFreq.lo = 25000000;
timerParams.extFreq.hi = 0;
timerParams.period = 2500000;
timerParams.periodType =ti_sysbios_interfaces_ITimer_PeriodType_MICROSECS;
timerParams.runMode = ti_sysbios_interfaces_ITimer_RunMode_CONTINUOUS;
timerParams.startMode = ti_sysbios_interfaces_ITimer_StartMode_AUTO;
timerParams.arg = (xdc_UArg)(&timerParams);
timer = Timer_create(Timer_ANY, App_TimerFxn, &timerParams, &eb);
上述代码，App_TimerFxn()执行周期大概0.25s执行。
如果改成如下配置：
timerParams.extFreq.lo = 50000000;
timerParams.extFreq.hi = 0;
timerParams.period = 2500000;
则App_TimerFxn()执行周期大概为0.5s。
如果改成如下配置：
timerParams.extFreq.lo = 50000000;
timerParams.extFreq.hi = 0;
timerParams.period = 5000000;
则App_TimerFxn()执行周期大概为1s。
我想问下周期是如何计算出来的？