这样配置定时器，输出的时钟频率是多少？应该怎么计算？

void TimerInit()
{
TimerDisable(TIMER2_BASE,TIMER_A);
GPIOPinTypeTimer(GPIO_PORTB_BASE,GPIO_PIN_0);
GPIOPinConfigure(GPIO_PB0_T2CCP0); //配置PB0为CCP模式
HWREG(TIMER2_BASE + TIMER_O_CFG) = 0x04; //选择16-bit timer

//配置TimerA周期计数(Periodic Timer mode)
HWREG(TIMER2_BASE + TIMER_O_TAMR)|=(TIMER_TAMR_TAAMS|TIMER_TAMR_TAMR_PERIOD) ;

//加载Timer计数值:40，并且设置Match值:20(Timer默认为减计数)
HWREG(TIMER2_BASE + TIMER_O_TAMATCHR) = 20;
TimerLoadSet(TIMER2_BASE,TIMER_A,40);

TimerEnable(TIMER2_BASE,TIMER_A); //使能Timer
}