RasClock v5.0 is a highly accurate real-time clock that plugs directly into the Raspberry Pi and includes a battery backup. The module is installed directly into the GPIO header pins with no wiring or soldering. It uses the 3.3V, GND SDA and SCL pins. The module stays within the outline of the Raspberry Pi and sits lower than video output so can be easilly installed within most cases.

RasClock uses one of the following chips:

• NXP PCF2127AT
• NXP PCF2127T
• NXP PCF2129AT
• NXP PCF2129T

RasClock features:

• Very accurate timekeeping (typically ±3ppm or <2 minutes deviation per year).
• Integrated crystal that compensates for temperature and age.
• The supplied 36mA 3V battery will keep the time for around two years if the device isn't used and considerably longer if it is.
• Coin Battery Included!
• Fits inside most cases easilly inclusing the ModMyPi Raspberry Pi Case, PiBow's and Multicomp Cases.

Why do I need a Real Time Clock for my Raspberry Pi?

Complete installation and set up instructions can be found at http://afterthoughtsoftware.com/products/rasclock

Additional tutorial can be found at https://www.modmypi.com/blog/installing-the-rasclock-raspberry-pi-real-time-clock

Set up is easy, simply follow the guide Outlined in the ModMyPi Raspberry Pi Tutorial Here!

How to check what version of hardware and software running on your Raspberry Pi:

pi@raspberrypi:/$ sudo bash
pi@raspberrypi:/# cat /proc/cpuinfo
Processor       : ARMv6-compatible processor rev 7 (v6l)
BogoMIPS        : 697.95
Features        : swp half thumb fastmult vfp edsp java tls
CPU implementer : 0x41
CPU architecture: 7
CPU variant     : 0x0
CPU part        : 0xb76
CPU revision    : 7

Hardware        : BCM2708
Revision        : 0003
Serial          : 00000000c0ae10d9

root@raspberrypi:/# cat /etc/debian_version
7.1

root@raspberrypi:/# uname -or
3.6.11+ GNU/Linux

How to configure RTC module and remove fake-hwclock (when using wheezy 3.6.11):

sudo bash

apt-get remove fake-hwclock
rm /etc/cron.hourly/fake-hwclock
update-rc.d -f fake-hwclock remove
rm /etc/init.d/fake-hwclock

rpi-update

wget http://afterthoughtsoftware.com/files/linux-image-3.6.11-atsw-rtc_1.0_armhf.de
dpkg -i linux-image-3.6.11-atsw-rtc_1.0_armhf.deb
cp /boot/vmlinuz-3.6.11-atsw-rtc+ /boot/kernel.img

echo "i2c-bcm2708" >> /etc/modules
echo "rtc-pcf2127a" >> /etc/modules

Add the following to /etc/rc.local before "exit 0":

# Referring to
# http://www.raspberrypi-spy.co....
# to get the RasPi board version:
REV=$(cat /proc/cpuinfo|grep Revision)
# Extract revision
REV=${REV##*: }
# Make it readable as hex
REV=0x$REV
# Convert hex to dec
REV=$((REV))
if [ $REV -lt 4 ]
then
  echo pcf2127a 0x51 > /sys/class/i2c-adapter/i2c-0/new_device
  echo setting rtc to i2c-0
else
  echo pcf2127a 0x51 > /sys/class/i2c-adapter/i2c-1/new_device
  echo setting rtc to i2c-1
fi
( sleep 2; hwclock -s ) &

Then reboot:

sync
reboot

Console should show similar to:

[   32.897890] rtc-pcf2127a 0-0051: chip found
[   32.899695] rtc-pcf2127a 0-0051: rtc core: registered rtc-pcf2127a as rtc0
[   32.899757] i2c i2c-0: new_device: Instantiated device pcf2127a at 0x51

Then later nearer the login prompt:

Board revision: X
setting rtc to i2c-X

Log back in and verify date is correct:

date

Set hardware clock to current system time:

sudo hwclock -w

Verify hardware clock is set correctly:

sudo hwclock -r