我有一个问题，在 AVR ATtiny84A上执行禁用看门狗序列实际上是在重置芯片，即使定时器应该有足够的时间。当在许多物理部件上运行相同的代码时，这种情况不一致；有的每次都重置，有的有时会重置，有的从不重置。

为了演示这个问题，我编写了一个简单的程序...

1. 使用 1 秒超时启用看门狗
2. 重置看门狗
3. 白色 LED 闪烁 0.1 秒
4. 白色 LED 闪烁 0.1 秒
5. 禁用看门狗

看门狗启用和禁用之间的总时间小于 0.3 秒，但有时在执行禁用序列时会发生看门狗复位。

这是代码：

#define F_CPU 1000000                   // Name used by delay.h. We are running 1Mhz (default fuses)

#include <avr/io.h>
#include <util/delay.h>
#include <avr/wdt.h>


// White LED connected to pin 8 - PA5

#define WHITE_LED_PORT PORTA
#define WHITE_LED_DDR DDRA
#define WHITE_LED_BIT 5


// Red LED connected to pin 7 - PA6

#define RED_LED_PORT PORTA
#define RED_LED_DDR DDRA
#define RED_LED_BIT 6


int main(void)
{
    // Set LED pins to output mode

    RED_LED_DDR |= _BV(RED_LED_BIT);
    WHITE_LED_DDR |= _BV(WHITE_LED_BIT);


    // Are we coming out of a watchdog reset?
    //        WDRF: Watchdog Reset Flag
    //        This bit is set if a watchdog reset occurs. The bit is reset by a Power-on Reset, or by writing a
    //        logic zero to the flag

    if (MCUSR & _BV(WDRF) ) {

        // We should never get here!


        // Light the RED led to show it happened
        RED_LED_PORT |= _BV(RED_LED_BIT);

        MCUCR = 0;        // Clear the flag for next time
    }

    while(1)
    {
        // Enable a 1 second watchdog
        wdt_enable( WDTO_1S );

        wdt_reset();          // Not necessary since the enable macro does it, but just to be 100% sure

        // Flash white LED for 0.1 second just so we know it is running
        WHITE_LED_PORT |= _BV(WHITE_LED_BIT);
        _delay_ms(100);
        WHITE_LED_PORT &= ~_BV(WHITE_LED_BIT);
        _delay_ms(100);

        // Ok, when we get here, it has only been about 0.2 seconds since we reset the watchdog.

        wdt_disable();        // Turn off the watchdog with plenty of time to spare.

    }
}

启动时，程序会检查之前的复位是否是由看门狗超时引起的，如果是，它会点亮红色 LED 并清除看门狗复位标志以指示发生了看门狗复位。我相信这段代码永远不应该被执行，红色 LED 也不应该亮起，但它经常会亮起。

这里发生了什么？