Problem using RTC using ds3231

Question

Trying to get an RTC to load at boot. I've enabled i2c, that works fine for other components.

/etc/modules contains:

snd-bcm2835
i2c-bcm2835
i2c-dev 
rtc-ds3231

/etc/rc.local contains:

echo ds3231 0x68 > /sys/class/i2c-adapter/i2c-1/new_device
hwclock -s

i2cdetect -y 1 shows UU in the 68 slot

I can set the date using hwclock with -r, '-w', and -s successfully

if I reboot, I get from hwclock -r

hwclock: The Hardware Clock registers contain values that are either invalid (e.g. 50th day of month) or beyond the range we can handle (e.g. Year 2095).

I can then write, read and sync with it again fine.

Any suggestions?! I've tried replacing the RTC module, but the same thing happens. Same if I remove the battery from the RTC.

If I remove the battery, the first time I boot it will show the date in the year 2000, but after that it'll go back to the error.

Answer 1

The answers involving modprobe and removing fake hwclock are not needed for Stretch era Rasbian and beyond. Here's the steps that work for me as a reference:

1. Install tools:

   sudo apt-get install -y i2c-tools   
   sudo apt-get install -y python-smbus
   

2. Update /boot/config.txt (Note: you can turn I2C 'on' via sudo raspi-config, but you need the overlay too to properly load the driver).

   sudo sh -c "echo dtoverlay=i2c-rtc,ds3231 >> /boot/config.txt"
   sudo sh -c "echo dtparam=i2c_arm=on >> /boot/config.txt"
   

3. Update /lib/udev/hwclock-set file (sudo nano /lib/udev/hwclock-set) and "comment out" the following lines ("comment out" means put a # at the beginning of each of the lines, so they become comments and are ignored by the system). They should like like:

   # if [ -e /run/systemd/system ] ; then
   # exit 0
   # fi
   

4. Reboot system

   sudo reboot
   

5. Review I2C is working, and get current timestamp from RTC:

   sudo i2cdetect -y 1 # will show 68 if I2C is on, but UU if overlay is actually active.
   sudo hwclock -r
   

6. Review and update reading from hw clock.

   sudo hwclock -D -r
   date # Get latest date from internet 
   sudo hwclock -w # write that date to HW clock
   sudo hwclock -r # read the value of hw clock again
   

References: https://learn.adafruit.com/adding-a-real-time-clock-to-raspberry-pi/set-rtc-time https://www.raspberrypi.org/forums/viewtopic.php?t=161133