Changes

= Overview = Real time clock (RTC) is a computer clock (most often in the form of an integrated circuit) that keeps track of the current time. RTCs are present in almost any electronic device which needs to keep accurate time. More general information [http://en.wikipedia.org/wiki/Real-time_clock here].<br>

* '''RTC System clock''': system clock is controlled by MPU using its internal RTC peripheral. Every boot-up, the default firmware (/etc/init.d/hwclock.sh) copies the hardware clock data from /dev/rtc to system clock data to keeps clock up to date.

** '''RTC battery is used''': PMIC RTC peripheral keeps hardware clock alive when OS isn't running and backup battery powers the backup state as far as the input voltage is high enough(at least 2 weeks into IGEPv2).

== Simplified RTC diagram == {| cellspacingborder="1" cellpaddingwidth="1150" widthcellspacing="1501" bordercellpadding="1" align="center"

|| [[Image:RTC diagram.png|800px|Block diagram from IGEP0033]]<br>

= Requirements = 

= Rectify clock drift= 

* ...

Software tools can be used to compensate these errors. Once you tested your implementation add some rule to [http://es.wikipedia.org/wiki/Cron_%28Unix%29 cron deamon] to automatize the process. Some available solutions are:

== Set the date and time via NTP ==If your board is connected to Internet regularly, this can be the most interesting workaround. The network time protocol (NTP) is the current widely accepted standard for synchronizing clocks over the Internet. NTP uses a hierarchical scheme in order to synchronize the clocks in the network.

===ntpd deamon===You should configure "/etc/ntp.conf" with appropriated Internet ntp server (for example: "server pool.ntp.org") To force time synchronization, it could be used [http://manpages.ubuntu.com/manpages/maverick/man8/ntpd.8.html ntpd daemon with "-q" option] (This behavior mimics that of the ntpdate(8) program) <pre>ntpd -d -c /etc/ntp.conf -q</pre>===(alternative) ntpdate program===Ntpdate program is not installed into firmware by default, use zypper program to download and install the package:

=== ntpd deamon =Rectify systematic error editing PMIC RTC registers==This workaround can be helpful when your board is not regularly connected to Internet. For this method we are going to:

=== Calculate systematic clock error === 

=== Rectify systematic clock error configuring PMIC RTC registers =======Overview====Now its time to compensated this delayed drift (+3.6 seconds/day) configuring PMIC RTC registers. The edited registers will be:

==== Overview ====Now its time to compensated this delayed drift (+3.6 seconds/day) configuring PMIC RTC registers. The edited registers will be:*RTC_CTRL_REG: Enables RTC compensation.**I2c bus: I2C1**Address: 0x4b**Register: 0x29*RTC_COMP_LSB_REG: 16 bits LSB of drift value (COM_REG) in ([http://en.wikipedia.org/wiki/Two%27s_complement Two's complement]).**I2c bus: I2C1**Address: 0x4b**Register: 0x2c*RTC_COMP_MSB_REG: 16 bits MSB of drift value (COM_REG) in ([http://en.wikipedia.org/wiki/Two%27s_complement Two's complement]).**I2c bus: I2C1**Address: 0x4b**Register: 0x2d

==== Calculate COM_REG value ==== If RTC_CTRL_REG autocompensation is enabled PMIC RTC peripheral compensates will compensate every hour and 1 second the clock drift using the COMP_REG value, It adds or substract a second. Use the The next formula shows how to calculate it:

Now pass your COMP_REG decimal value to 16 bit hexadecimal, in my case was 0X1333(4915). COMP_REG  ====Edit registers====Registers will be added to edited using the RTC 32i2c-kHz countertools, the duration of the current second becomes [(32,768 – COMP_REG)/32,768] seconds; therefore, it these registers will be saved until RTC source is possible to compensate the RTC with 1/32,768-second time unit accuracy each hour.not active:

 <pre>i2cset -f -y 1 0x4b 0x2d 0x13

==== Correct system clock ====Hardware clock will be compensated automatically, to transfer hardware clock to system clock is necessary use hwclock command: