Lahorde/0_README.md

## 0_README.md

      
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              0_README.md
            
          
    Description

Enable i2c RTC using systemd.
A udev rules triggers an I2C systemd service on I2C kernel module adding.
Service then loads I2C driver adding a new I2C device to /sys
Then kernel loads I2C RTC driver and adds an RTC device
It triggers a udev rules that updates hardware clock
Application on raspberry pi

Enable I2C


enable I2C in config.txt, adding device_tree_param=i2c1=on


enable I2C driver loading at boot, refer i2c.conf


reboot raspberry


check an I2C bus is found :
i2cdetect -l
i2c-1   unknown         bcm2835 I2C adapter                     N/A


check I2C rtc is detected :
i2cdetect -y 1
0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --          


Enable I2C RTC


create /etc/udev/rules.d/50-i2c_start.rules


create /etc/conf.d/rtc-i2c


create /etc/systemd/system/i2c_rtc.service


create /etc/udev/rules.d//etc/udev/rules.d/60-rtc-i2c.rules


test it:
hwclock -r
2000-01-02 01:25:04.301281+01:00


when an NTP service is started, it should set hwclock to a valid time, if not you must set a valid system clock and then set hwclock to system clock
hwclock --systohc


reboot


system clock should be fine, even if system is not connected to outside world


## 50-i2c_start.rules
# /etc/udev/rules.d/50-i2c_start.rules
#
#
#I2C hardware device driver
ACTION=="add", KERNEL=="i2c_bcm2708", SUBSYSTEM=="module", TAG+="systemd"

## 60-rtc-i2c.rules
# /etc/udev/rules.d/60-rtc-i2c.rules
#
#
ACTION=="add", SUBSYSTEM=="rtc", ATTRS{hctosys}=="0", RUN+="/usr/bin/hwclock -s --utc"

## i2c-rtc
#/etc/conf.d/rtc-i2c
# configure there your RTC chip and address
CHIP="ds1307"
ADDRESS="0x68"
BUS="1"

## i2c.conf
# /etc/modules.load.d/i2c.conf
i2c-bcm2708
i2c-dev

## i2c_rtc.service
# /etc/systemd/system/i2c_rtc.service

[Unit]
Description=Initialize i2c hardware RTC device driver
DefaultDependencies=no
Requires=sys-module-i2c_bcm2708.device
After=sys-module-i2c_bcm2708.device
Conflicts=shutdown.target

[Service]
Type=oneshot
RemainAfterExit=yes
EnvironmentFile=/etc/conf.d/rtc-i2c
ExecStart=/bin/sh -c "echo ${CHIP} ${ADDRESS} > /sys/class/i2c-adapter/i2c-${BUS}/new_device"
	# /etc/udev/rules.d/50-i2c_start.rules
	#
	#
	#I2C hardware device driver
	ACTION=="add", KERNEL=="i2c_bcm2708", SUBSYSTEM=="module", TAG+="systemd"
	# /etc/udev/rules.d/60-rtc-i2c.rules
	#
	#
	ACTION=="add", SUBSYSTEM=="rtc", ATTRS{hctosys}=="0", RUN+="/usr/bin/hwclock -s --utc"
	#/etc/conf.d/rtc-i2c
	# configure there your RTC chip and address
	CHIP="ds1307"
	ADDRESS="0x68"
	BUS="1"
	# /etc/systemd/system/i2c_rtc.service

	[Unit]
	Description=Initialize i2c hardware RTC device driver
	DefaultDependencies=no
	Requires=sys-module-i2c_bcm2708.device
	After=sys-module-i2c_bcm2708.device
	Conflicts=shutdown.target

	[Service]
	Type=oneshot
	RemainAfterExit=yes
	EnvironmentFile=/etc/conf.d/rtc-i2c
	ExecStart=/bin/sh -c "echo ${CHIP} ${ADDRESS} > /sys/class/i2c-adapter/i2c-${BUS}/new_device"