.. include:: ../substitutions.rst

.. _uartBoot-62:

UART
====

During development, it may be beneficial to leverage the primary UART debug interface for loading your boot binaries onto the |product| development kit. This guide will walk through the process of booting into U-Boot via UART.

Preparing the Development Kit
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The |product| development kit is configured to boot from an SD Card slot by default and basic steps for performing this and establishing serial communication are outlined in the :ref:`Quickstart-62`.
We need to modify the default boot configuration to UART Boot AND connect the development kit's Debug UART interface to your Ubuntu Host Machine (these steps are not currently supported from a Windows Host Environment).

* S7 should be ON to override the default boot settings.

.. image:: ../../images/phycore-am62x/pb-07124_boot-uart.png
    :width: 350px
    :alt: UART Boot Switch Settings

.. image:: ../../images/phycore-am62x/pb-07124_bootswitch.png
    :width: 500px
    :alt: phyBOARD-AM62x Boot Switch Location

* Once configured, connect your |product| development kit's Debug UART interface to your **Ubuntu Host Machine**. This can typically be done in the Virtual Machine settings but exact steps vary depending on the VM software you are using.

.. note::

  This guide assumes the following:
    #. The **console** is connected to **ttyUSB0** of the Ubuntu Host Machine.
    #. **lrzsz** package is installed on the Ubuntu Host Machine. To install lrzsz, run:

    .. code-block:: console
      :substitutions:

      |host-prompt| sudo apt update && sudo apt install lrzsz

* Make sure you are part of the ``dialout`` group.

    .. code-block:: console
      :substitutions:

      |host-prompt| sudo usermod -a -G dialout <username>

.. note::

  You may need to restart your computer for the dialout permission to take effect.


* Power-on the development kit.
* To test your setup thus far, open a serial console within your Ubuntu Host Machine:

  * Use the following command to start a serial connection with the development kit:

    .. code-block:: console
      :substitutions:

      |host-prompt| minicom -b 115200 -D /dev/ttyUSB0

  * In UART Boot mode, you should see the following string of characters printed to the terminal:

    .. code-block:: none
      :substitutions:
      :caption: minicom Session

      01000000011a0000616d36327800000000000000475020200100010001000100C

  * You should also see the final "C" character continuously printed to the terminal.
  * You must now close the minicom session for the remaining steps to work. To close minicom, first enter Ctrl-A and then hit the X key (Ctrl-A and then the Z key will give you a command reference for more options).

Loading the Bootloader Binaries
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Enter the following commands in your Ubuntu Host Machine in order to load the multiple stages of the bootloaders in sequence. The files can be found at :ref:`PreBuilts-62` or built using :ref:`BuildTheBSP-62`. Be sure to replace the "<path to>" substring within each command to reflect the appropriate filesystem path your build system has these files stored.

  .. code-block:: console
    :substitutions:

    |host-prompt| stty -F /dev/ttyUSB0 115200
    |host-prompt| sb --xmodem <path to>/tiboot3.bin > /dev/ttyUSB0 < /dev/ttyUSB0
    |host-prompt| sb --ymodem <path to>/tispl.bin > /dev/ttyUSB0 < /dev/ttyUSB0
    |host-prompt| sb --ymodem <path to>/u-boot.img > /dev/ttyUSB0 < /dev/ttyUSB0

Once complete, you can reopen minicom to access the U-Boot console:

  .. code-block:: console
    :substitutions:

    |host-prompt| minicom -b 115200 -D /dev/ttyUSB0