Adafruit: RTC DS1307
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.
On boot BBB is connected power from the DC power adapter, therefore it loads the correct /dev/rtc modules.
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
clock_init.sh sets up the RTC if it has never been set up before. If the BBB internal clock is lost, the script will copy the time over from the RTC. If the BBB is set up correctly the script will copy update the time from ntp servers, and write that time to the RTC module.
#!/bin/bash a=$(date +%Y) 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 # Sets time zone to Eastern (GMT -5) $( ln -sf /usr/share/zoneinfo/America/New_York /etc/localtime ) echo "The new date is:" $(date)