使用Arduino UNO的看门狗：

    介绍：看门狗定时器用避免电子设备出现故障造成死机，例如死循环。为此，看门狗作为一个物理定时器，在程序运行时不断的增加，并驱动一个中断， 如果达到某一个设定的值，就会复位微处理器。在正常操作下，定时器在程序流程中的定期设置为0， 但如果代码进入死循环，定时器复位不会发生，看门狗触发中断并重新启动。

    使用看门狗防止死机：Arduino为用户提供了方便操作的函数和宏，可以直接引入库：

#include <avr/wdt.h>

    这个函数库提供了三个API函数供我们使用：

wdt_enable(timeout) //看门狗使能并设置超时时间

wdt_disable() //关闭

wdt_reset() //复位

timeout可以使用wdt.h文件中定义的宏常量，也可以自定义时间；

通常情况下，需要在setup（）函数中使能看门狗定时器，并在loop（）中不断的喂狗防止溢出，官方给出的示例代码如下：

#include <avr/wdt.h>

void setup()

{

   pinMode(13,OUTPUT);

   wdt_enable(WDTO_2S); //开启看门狗，并设置溢出时间为两秒

}

void loop()

{

   digitalWrite(13,HIGH);

   delay(100);

   digitalWrite(13,LOW);

   delay(100);

   wdt_reset(); //喂狗操作，使看门狗定时器复位

}

注：看门狗也可以唤醒省电模式下的 Arduino， 详细说明可查阅官方文档，特别指出的是，如果使用POWER_MODE_IDLE模式（UART、SPI、timer等处于工作状态），需在进入休眠状态前关闭看门狗功能，休眠结束之后再次启动，否则几秒之后看门狗会强制重启Aruino， 休眠失败。示例代码：

/* Sleep Demo Serial

 * -----------------

 * Example code to demonstrate the sleep functions in a Arduino. Arduino will wake up

 * when new data is received in the serial port USART

 * Based on Sleep Demo Serial from http://www.arduino.cc/playground/Learning/ArduinoSleepCode

 *

 * Copyright ? 2006 MacSimski 2006-12-30

 * Copyright ? 2007 D. Cuartielles 2007-07-08 - Mexico DF

 *

 * With modifications from Ruben Laguna 2008-10-15

 *

 * This program is free software: you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation, either version 3 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program. If not, see <http://www.gnu.org/licenses/>.

 *

 */

#include <avr/power.h>

#include <avr/sleep.h>

int sleepStatus = 0; // variable to store a request for sleep

int count = 0; // counter

void setup()

{

Serial.begin(9600);

}

void sleepNow()

{

/* Now is the time to set the sleep mode. In the Atmega8 datasheet

 * http://www.atmel.com/dyn/resources/prod_documents/doc2486.pdf on page 35

 * there is a list of sleep modes which explains which clocks and

 * wake up sources are available in which sleep modus.

 *

 * In the avr/sleep.h file, the call names of these sleep modus are to be found:

 *

 * The 5 different modes are:

 * SLEEP_MODE_IDLE -the least power savings

 * SLEEP_MODE_ADC

 * SLEEP_MODE_PWR_SAVE

 * SLEEP_MODE_STANDBY

 * SLEEP_MODE_PWR_DOWN -the most power savings

 *

 * the power reduction management <avr/power.h> is described in

 * http://www.nongnu.org/avr-libc/user-manual/group_avr_power.html

 */

set_sleep_mode(SLEEP_MODE_IDLE); // sleep mode is set here

sleep_enable(); // enables the sleep bit in the mcucr register

// so sleep is possible. just a safety pin

power_adc_disable();

power_spi_disable();

power_timer0_disable();

power_timer1_disable();

power_timer2_disable();

power_twi_disable();

wdt_disable(); //close wdt before Arduino enter sleep mode

sleep_mode(); // here the device is actually put to sleep!!

// THE PROGRAM CONTINUES FROM HERE AFTER WAKING UP

sleep_disable(); // first thing after waking from sleep:

// disable sleep...

wdt_enable(timeout); //open wdt after wakine from sleep

power_all_enable();

}

void loop()

{

// display information about the counter

Serial.print("Awake for ");

Serial.print(count);

Serial.println("sec");

count++;

delay(1000); // waits for a second

// compute the serial input

if (Serial.available()) {

int val = Serial.read();

if (val  'S') {

      Serial.println("Serial: Entering Sleep mode");

      delay(100);     // this delay is needed, the sleep

                      //function will provoke a Serial error otherwise!!

      count = 0;

      sleepNow();     // sleep function called here

    }

    if (val  'A') {

Serial.println("Hola Caracola"); // classic dummy message

}

}

// check if it should go asleep because of time

if (count >= 10) {

Serial.println("Timer: Entering Sleep mode");

delay(100); // this delay is needed, the sleep

//function will provoke a Serial error otherwise!!

count = 0;

sleepNow(); // sleep function called here

}

}