MSP432E401Y: MSP432P401定时器TA选择外部时钟源TACLK，无法计数

MSP432P401定时器TA选择外部时钟源TACLK，无法计数。已经根据数据手册配置了GPIO7.2作为TA1CLK，可是当我让一个VP=3.3V，VN=0V，占空比50%的PWM输入到该引脚后，发现，定时器不计数。请问哪个环节出现了错误？

下面是我的配置代码

const Timer_A_ContinuousModeConfig continuousModeConfig =
{
        TIMER_A_CLOCKSOURCE_EXTERNAL_TXCLK,           // ACLK Clock Source
        TIMER_A_CLOCKSOURCE_DIVIDER_1,      // ACLK/1 = 32.768khz
        TIMER_A_TAIE_INTERRUPT_ENABLE,      // Enable Overflow ISR
        TIMER_A_DO_CLEAR                    // Clear Counter
};

int main(void)
{
    /* Stop watchdog timer */
    MAP_WDT_A_holdTimer();

    /* Configuring P1.0 as output */
    MAP_GPIO_setAsOutputPin(GPIO_PORT_P1, GPIO_PIN0);
    MAP_GPIO_setOutputLowOnPin(GPIO_PORT_P1, GPIO_PIN0);

    /* Starting and enabling ACLK (32kHz) */
    MAP_CS_setReferenceOscillatorFrequency(CS_REFO_128KHZ);
    MAP_CS_initClockSignal(CS_ACLK, CS_REFOCLK_SELECT, CS_CLOCK_DIVIDER_4);

    /* Configuring Continuous Mode */
    MAP_GPIO_setAsPeripheralModuleFunctionInputPin(GPIO_PORT_P7,GPIO_PIN2, GPIO_PRIMARY_MODULE_FUNCTION);//设置GPIO复用

    MAP_Timer_A_configureContinuousMode(TIMER_A1_BASE, &continuousModeConfig);

    /* Enabling interrupts and going to sleep */
    MAP_Interrupt_enableSleepOnIsrExit();
    MAP_Interrupt_enableInterrupt(INT_TA1_N);
    
    /* Enabling MASTER interrupts */
    MAP_Interrupt_enableMaster();  

    /* Starting the Timer_A0 in continuous mode */
    MAP_Timer_A_startCounter(TIMER_A1_BASE, TIMER_A_CONTINUOUS_MODE);

    while(1)
    {
        MAP_PCM_gotoLPM0();
    }

}

//******************************************************************************
//
//This is the TIMERA interrupt vector service routine.
//
//******************************************************************************
void TA1_N_IRQHandler(void)
{
    MAP_Timer_A_clearInterruptFlag(TIMER_A1_BASE);
    MAP_GPIO_toggleOutputOnPin(GPIO_PORT_P1, GPIO_PIN0);
}