Adafruit: RTC DS1307

Overview
Adafruit's DS1307 Real-Time Clock Breakout Kit uses a Maxim Integrated DS1307. The DS1307 can be used to store a the date and time. It may lose or gain 2 seconds a day.

Inputs and Outputs
The RTC must be powered from the BeagleBone's 5V supply (note it must be powered from the DC adapter, or else I2C bus will hang, as there is not enough current provided by the usb bus to power the RTC). The RTC uses an I2C interface to communicate with the BBB.

Bone Wiring
On boot BBB is connected power from the DC power adapter, therefore it loads the correct /dev/rtc modules.

Pin mappings:

P9 pin # (BeagleBone pin) -> Panel pin (wire color)

1 (GND) -> GND

5 (VDD_5V) -> VCC

5 (VDD_5V) -> SQW (through 10k pullup resistor)

19 (I2C2_SCL) -> SCL

20 (I2C2_SCL) -> SDA

Sample Code
This code was adapted from Adafruit's sample code, and can be found at Alex Alvarez's github repository.

clock_init.sh
interacts with the RTC:
 * if the host is out of date -- reads from the RTC, and overwrites the system clock
 * if the host is not out of date -- updates systemclock from ntp, and overwrites the RTC from systemclock so as to account for adding +/- 2 seconds daily.

a=$(date +%Y)
 * 1) !/bin/bash

if $a < 2013 ; then echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-1/new_device echo "Retrieving time from rtc" hwclock -s -f /dev/rtc1 hwclock -w

echo "Date has been read from RTC, and copied to system clock" else # Assumes if date is correct on reboot, that you are connected to network echo "Fetching time from ntp server" $(/usr/bin/ntpdate -b -s u pool.ntp.org)

if [ -e /dev/rtc1 ]; then echo "Writing system clock to RTC" hwclock -w -f /dev/rtc1 else echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-1/new_device echo "Writing system clock to RTC" hwclock -w -f /dev/rtc1 fi fi

$( ln -sf /usr/share/zoneinfo/America/New_York /etc/localtime ) echo "The new date is:" $(date)
 * 1) Sets time zone to Eastern (GMT -5)

NOTE: change ln -sf /usr/share/zoneinfo/*/* /etc/localtime  #as needed for your local timezone

serviceSetup.sh
This file manipulates the rtc-ds1307.service to run from a paramaterized directory. It copies over clock_init.sh, and rtc-ds1307.service to the given directory, and manipulates the variables inside of the service file to react accordingly. It then enables the service, so that it will run at startup.

In order to manually start the service execute: systemctl start rtc-ds1306.service and stop: systemctl stop rtc-ds1306.service


 * 1) !/bin/bash
 * 2) By Alex Alvarez, alvarep@rose-hulman.edu
 * 3) This script creates a new directory if passed as the parameter, and places the rtc script and service files in those given directories. It also manipulates the service file such that the working directories change with the given directory parameter.
 * 4) If no paramter is given the working directory is used as the service location

if [ "$1" ]; then

DIR=$1 $(mkdir $1)

else

DIR=$(pwd) fi

SED_ARG="-e 's@WorkingDirectory=.*@WorkingDirectory=$DIR@' rtc-ds1307.service"

eval sed "$SED_ARG" > tmp.txt

mv tmp.txt rtc-ds1307.service

cp rtc-ds1307.service $DIR cp clock_init.sh $DIR

systemctl enable $DIR/rtc-ds1307.service

rtc-ds1307.service
[Unit] Description=DS1307 RTC Service

[Service] Type=simple WorkingDirectory=/usr/share/rtc_ds1307 ExecStart=/bin/bash clock_init.sh SyslogIdentifier=rtc_ds1307

[Install] WantedBy=multi-user.target