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#!/usr/bin/env python
import os
import sys
import datetime
import readline
from exceptions import OSError
DEVICE_I2C_ID = 0x68 # i2cdetect speaks hex, easier to keep
# everything uniform.
DEVICE_NAME = 'ds1307'
RTC configuration script for DS1307/Raspberry Pi
Automatically detects an installed DS1307 on either I2C bus and sets it up as
the hardware RTC if that's not already been done.
Domhnall Walsh, 091 Labs
def shell_execute(command):
""" Run a shell command and raise an exception if it doesn't work. """
import commands
result_code, output = commands.getstatusoutput(command)
# Make sure that the command actually ran successfully...
if result_code != 0:
raise RunTimeException(
"Failed to execute command '%s' - code %s, message %r" %
(command, result_code, output))
return output
def enumerate_i2c_buses():
""" Return a list of the names of all the i2c buses known to i2cdetect. """
shell_command = 'i2cdetect -l'
return [row.split('\t')[0] for row in
except OSError:
return []
def scan_i2c_bus(id):
""" Return a list of devices that are on the specified I2C bus.
Returns a dictionary with the hardware addresses as keys (e.g. "0x68")
and how i2cdetect detects them as their value - their address in hex if
not already in use, or "UU" for unavailable.
shell_command = 'i2cdetect -y %d' % id
i2c_devices = {}
results = shell_execute(shell_command).split('\n')[1:]
except OSError:
return []
for row in results:
row_offset = int(row[:2], 16) # Addresses are all in hex...
if row_offset == 0:
row_index = 3
row_index = 0
row_data = [i.strip() for i in row[4:].strip().split(" ")]
for value in row_data:
address = hex(row_offset + row_index)
if value != "--": # i2cdetect: "--" = no device at address
i2c_devices[address] = value
row_index += 1
return i2c_devices
if __name__ == '__main__':
# Make sure this program only runs as root.
if not os.geteuid() == 0:
sys.exit("\nOnly root can run this script\n")
# Get the i2c bus IDs and extract the numerical portions from those.
i2c_buses = enumerate_i2c_buses()
i2c_bus_ids = [int(bus[-1]) for bus in i2c_buses]
device_found = False
for bus in i2c_buses:
bus_id = int(bus.split('-')[-1])
device_addresses = scan_i2c_bus(bus_id)
# Check if there's a device at the address specified.
device_id_string = "%#x" % DEVICE_I2C_ID
if device_id_string in device_addresses.keys():
device_found = True
# Need to check if the device is in use or not...
if device_addresses[device_id_string] == "UU":
# Device is in use...
print "Device at address %#x already in use/known to system, "\
"skipping setup." % DEVICE_I2C_ID
print "%s found on I2C bus %s. Testing that we can read the " \
"clock..." % (DEVICE_NAME, bus)
# Register RTC as hardware clock.
shell_command = "echo %s 0x%d > " \
"/sys/class/i2c-adapter/%s/new_device" % \
print "Hardware RTC registered successfully. " \
"Checking time from RTC..."
except OSError, e:
sys.exit("\nFailed: %s\n" % e.message)
if not device_found:
sys.exit("\nFailed to find RTC module on I2C bus. Sorry.\n")
# If we get to there, we have a clock. Let's check if we can read it...
rtc_output = shell_execute('hwclock -r').split(" ")[0]
# need to lose the error factor...
# Tue 22 Jan 2013 13:36:34 GMT -0.073809 seconds
rtc_output = output.split(" ")[0]
# This removes the "... seconds" bit on the end
rtc_time = datetime.datetime.strptime(
rtc_output, "%a %d %b %Y %H:%M:%S %Z")
print "RTC time is: %s" % rtc_time
except OSError, e:
sys.exit("\nFailed to read RTC. Got error: %s\n" % e.message)
# Now get the time the system thinks it is...
system_time =
system_time.millis = 0
print "System time is: %s" % system_time
# datetime.timedelta's behaviour when it comes to subtracting a larger
# datetime from a smaller one is weird. This works though.
delta = abs(rtc_time - system_time)
print "Difference is %d seconds" % delta.seconds
print "(To update the system clock from the RTC, " \
"run 'hwclock --hctosys' as root)"
# TODO: Update /etc/rc.local if required to specify that the hardware clock
# is installed. See for more:
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