RTC
===

This guide will show you how to use rtc0 on the phyCORE-AM62Ax development kit to verify functionality when power is lost. To learn more information about the phyCORE-AM62Ax RTC interface, please see section 12.4 in the `Hardware Manual <https://www.phytec.com/product/phycore-am62a/#section-hardware-documentation>`_.


RTC Naming
------------

.. note::
    rtc0 is named after the physical IC populated on the SOM at U19.

* Verify the name of the RTC device by checking the name file in the interface’s sysfs directory:

.. code-block:: none
    :caption: Target (Linux)

    cat /sys/class/rtc/rtc0/name

.. code-block:: none
    :caption: Expected Output

    root@phyboard-lyra-am62axx-2:~# cat /sys/class/rtc/rtc0/name
    rtc-rv3028 0-0052

Setting the System Time
------------------------

* Set the RTC time by first setting the system time. We can do this manually or leverage the Network Time Protocol (NTP):

Manually
~~~~~~~~~

* Use the following command to set an arbitrary time as the system time in Linux:

.. code-block:: none
    :caption: Target (Linux)

    date 071916142016


.. note::
    The argument in the above command broken down is:

    07-19    16:14     2016

    date       time      year

Setting the RTC
-----------------
* With the system time set according to the above steps, you can now write this time to the RTC using the following command:

.. code-block:: none
    :caption: Target (Linux)

    hwclock -w -f /dev/rtc0

Reading the RTC
----------------

* The RTC's time can be read using the following command:

.. code-block:: none
    :caption: Target (Linux)

    hwclock -r -f /dev/rtc0

* The time set here should persist between boots and times without power as long as the VBAT pin of the SOM is supplied.


.. warning::
    A new SOM with an unprogrammed rtc may throw errors when read:

    .. code-block:: none
        :caption: Expected Output

        root@phyboard-lyra-am62axx-2:~# hwclock -r -f /dev/rtc0
        hwclock: ioctl(RTC_RD_TIME) to /dev/rtc0 to read the time failed: Invalid argument

    Set the RTC time according to the steps above to resolve this.

.. code-block:: none
 :caption: Expected Output

  root@phyboard-lyra-am62axx-2:~# hwclock -r -f /dev/rtc0
  Tue Jul 19 16:16:34 2016  0.000000 seconds