1.编辑/boot/config.txt 在末尾加入
dtparam=i2c_arm=on
dtoverlay=i2c-rtc,ds3231
2.在/etc/modules文件中添加一行：
i2c-dev
3.sudo apt-get install i2c-tools
4.sudo i2cdetect -y 1
5.sudo dpkg --purge fake-hwclock
6.sudo ntpdate cn.pool.ntp.org
7.sudo hwclock -w //将系统时钟写入硬件时钟
8.sudo hwclock -s //时钟芯片写入系统时钟
9.sudo nano /lib/systemd/system/hwclock-start.service
[Unit]
Description=Set time from RTC on startup
After=network.target
[Service]Type=oneshot
ExecStart=/sbin/hwclock -s
TimeoutSec=0
[Install]WantedBy=multi-user.target
10.sudo nano /lib/systemd/system/hwclock-stop.service
[Unit]
Description=Synchronise Hardware Clock to System Clock
DefaultDependencies=no
Before=shutdown.target
[Service]Type=oneshot
ExecStart=/sbin/hwclock --systohc
[Install]WantedBy=reboot.target halt.target poweroff.target
11.sudo systemctl enable hwclock-start hwclock-stop
资料来源：http://www.geek-workshop.com/thread-24954-1-1.html
奇怪啊。我的/etc/rc.local为啥不运行啊。。。。