View source for Tiny RTC I2C

=Add RTC support in Dragino openwrt=

[[File:Tiny_RTC_I2C.png|200px|none|Tiny RTC I2C module]]

==Modify Kernel==
In openwrt source , run 
 make kernel_menuconfig

and select:
 kernel_menuconfig 
 –>Device Drivers 
 –>Real Time Clock 
 +Set the RTC time based on NTP synchronization 
 +/sys/class/rtc/rtcN (sysfs) 
 +/proc/driver/rtc (procfs for rtcN) 
 +/dev/rtcN (character devices) 
 +Dallas/Maxim DS1307/37/38/39/40, ST M41T00, EPSON RX-8025 
 *tips: 
 -Set system time from RTC on startup and resume 
 disable this to avoid below error: 
 [ 2.960000] drivers/rtc/hctosys.c: unable to open rtc device (rtc0) 


==Add I2C and hwclock==
In openwrt source , run
 make menuconfig

and select
 –>kernel support 
 –>I2C support 
 +kmod-i2c-core 
 +algo-bit，i2c-gpio; 
 +kmod-i2c-gpio-custom

Add detect tool 
 –>Utilities  
 +hwclock 
 +i2c-tools

==All in one ==
if menuconfig has below option: 
 –>kernel modules–>other modules 
 kmod-rtc-ds1307

that will work well and no need the first step

=Hardware connection=
 Connect 3.3v to Dragino 3.3v
 Connect GND to Dragino GND
 Connect SDA to Dragino GPIO18
 Connect SCL to Dragino GPIO22

Can use other pins for SDA and SCL, need to change the I2C command in below. 

=Compile the image and test=
<syntaxhighlight lang="bash">
root@dragino-162054:/# 
root@dragino-162054:/# insmod i2c-dev
[  106.940000] i2c /dev entries driver
root@dragino-162054:/# insmod i2c-gpio-custom bus0=0,18,22
[  117.220000] Custom GPIO-based I2C driver version 0.1.1
[  117.240000] i2c-gpio i2c-gpio.0: using pins 18 (SDA) and 22 (SCL)
root@dragino-162054:/# i2cdetect -y 0
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: 50 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                         
root@dragino-162054:/# echo ds1307 0x68 > '/sys/class/i2c-dev/i2c-0/device/new_d
evice'
[  169.710000] rtc-ds1307 0-0068: SET TIME!
[  169.710000] rtc-ds1307 0-0068: rtc core: registered ds1307 as rtc0
[  169.720000] rtc-ds1307 0-0068: 56 bytes nvram
[  169.720000] i2c i2c-0: new_device: Instantiated device ds1307 at 0x68
root@dragino-162054:/# hwclock -r 
Sat Jan  1 00:00:31 2000  0.000000 seconds
root@dragino-162054:/# hwclock -r 
Sat Jan  1 00:00:36 2000  0.000000 seconds
root@dragino-162054:/# hwclock -r 
Sat Jan  1 00:00:38 2000  0.000000 seconds
</syntaxhighlight>

=Work Example Image=
This image is a working image : [http://www.dragino.com/downloads/test/firmware/IoT--build--v3.4.0--20170220-I2C-RTC/ LINK]