完成功能C后可变复位

Question

我正在尝试使用CTC和外部中断来启动计时器，该计时器将计数到60秒，并使用一个函数在ATmega128上显示LED的输出。该函数如下所示，在调试时将一直计入到十位的第一次迭代，但在下一次运行时，十位变量被重置为零，我无法理解它为什么重置。任何人都可以看到我可能在哪里犯了错误吗？

    #include <avr/io.h>
    #include <inttypes.h>
    #include <avr/interrupt.h>
    #include <util/delay_basic.h>

    volatile uint8_t passval = 0;

    void display(uint8_t value);

    int main(void)
    {
        DDRC = 0xFF;                                //PORTC output for two seven segment displays(tenths and ones place)
        DDRD = 0x0F;                                //PORTD output for one seven segment display(tens place)

        EICRA = ((1 << ISC01) | (1 << ISC00) | (1 << ISC11) | (1 << ISC10));        //Interrupt set to trigger on rising edge for PINA1...0
        TCCR1B |= (1 << WGM12);                     //Sets CTC Mode
        OCR1A = 24999;                              //Prescaler as 64 with a count of 25000
        TCNT1 = 0;                                  //Clears clock
        TIMSK |= (1 << OCIE1A);                     //Enables interrupt
        sei();                                      //Enable Global Interrupt

        while (1) 
        {   
            TCCR1B |= ((1 << CS11) | (1 << CS10));
            display(passval);
        }
        return 0;
    }

    void display(uint8_t value)
    {
        static uint8_t tenths, ones, tens;

        tenths = value;
        if (tenths > 0x09)                          //Rolls Over tenths place at 10
        {
            passval = 0x00;
            tenths = 0x00;
            ones++;                                 //Advances ones place
            if (ones > 0x09)                        //Rolls over ones places at 10
            {
                ones = 0x00;
                tens++;                             //Advances tens place

                if (tens > 0x06)                    //Rolls over tens place at 6
                {
                    tens = 0x00;
                }
            }
        }
        PORTC = ((ones << 4) + tenths);             //Display Output
        PORTD = tens;
    }

    ISR (TIMER1_COMPA_vect)                         //Timer ISR
    {
        passval++;                                  //Advance tenths place
    }