.. _run-app-hello:



Build and run of a simple hello world application on the Cortex®-M4/7
=====================================================================



Building the firmware
---------------------

Please read the chapter 'Run a demo using Arm GCC' from the document 'Getting Started with MCUXpresso SDK for EVK-MIMX8xx'.

To build the hello world sample, open a new terminal window and change the directory to the example application project directory,
which has a path similar to the following:

<sdk_install_dir>/boards/<board_name>/<example_type>/<application_name>/armgcc

In case of the hello world sample the directory is:

<sdk_install_dir>/boards/evkmimx8mm/demo_apps/hello_world/armgcc

run one of the available build scripts, for example:

.. prompt::
   :prompts: $

   ./build_debug.sh

The script should end with the messages:

.. code-block:: text

   [100%] Linking C executable debug/hello_world.elf
   Memory region         Used Size  Region Size  %age Used
       m_interrupts:         576 B        576 B    100.00%
             m_text:       13516 B     130496 B     10.36%
             m_data:        2224 B       128 KB      1.70%
             m_data2:          0 GB        16 MB      0.00%
   [100%] Built target hello_world.elf


Deploying the firmware to the target
------------------------------------
To start the firmware, we have to deploy it first to the target's memory. That could be basicly, the internal
emmc device of the SOM or the SD-card of the base board. The following example shows, how to deploy the firmware
to the internal emmc device.

After building the yocto Linux and programming it with the uuu-tool to the target, we can examine the programmed partitions inside U-Boot:

.. prompt::
   :prompts: U-Boot>

   part list mmc ${mmcdev}

.. code-block:: text

   Partition Map for MMC device 0  --   Partition Type: EFI
   Part   Start LBA       End LBA         Name
          Attributes
          Type GUID
          Partition GUID
          1     0x00000800      0x000107ff      "boot"
          attrs:  0x0000000000000000
          type:   ebd0a0a2-b9e5-4433-87c0-68b6b72699c7
          type:   data
          guid:   d117f98e-6f2c-d04b-a5b2-331a19f91cb2
          2     0x00010800      0x0075fbff      "rootfs"
          attrs:  0x0000000000000000
          type:   ebd0a0a2-b9e5-4433-87c0-68b6b72699c7
          type:   data
          guid:   0cc66cc0-5458-384d-1610-726f6f746673


The "boot"-partition contains the Linux- image and device trees. To store the firmware binary into that partition
we use the USB Mass Storage U-Boot function to mount that partition to our Linux host PC:

.. prompt::
   :prompts: U-Boot>

   ums 0 mmc ${mmcdev}:1

.. prompt::
   :prompts: $

   sudo mount /dev/sdX /mnt

Copy the file hello_world.bin to the mounted boot-partition.

Unmount this partition:

.. prompt::
   :prompts: $

   sudo umount /mnt

Stop the ums-device with :kbd:`CTRL` + :kbd:`C` in U-Boot.

List the contents of the boot-partition from U-Boot to check it:

.. prompt::
   :prompts: U-Boot>

   ls mmc ${mmcdev}

.. code-block:: text

   15759368   Image
   37178   imx8mm-tx8m-1610.dtb
   41437   imx8mm-tx8m-1610-mipi-mb.dtb
   14192   hello_world.bin

   4 file(s), 0 dir(s)


Starting the firmware
---------------------

The hello-world-sample uses the pins UART4_TXD and UART4_RXD to communicate to the outside world.
As you can see in the source file pin_mux.c, the Cortex®-M4/7 firmware handles the setup of the pinmux- and
the pad-registers by itself. That means, if you will start a Linux image on the Cortex®-A53 later,
you have to ensure that the devices that are used by the Cortex®-M4/7 firmware are disabled in the Linux device tree.

Looking into the TX8M-Datasheet document, you will find these two signals on the module pins 65 and 66.
Please note, these are 3,3V pins. Use a second TTL to USB Serial Converter cable to connect to the UART4 interface.
Start a serial terminal on your host, e.g. minicom, with the parameters 115200 -8N1.

Three steps are necessary to start the firmware:

#) copy the firmware from mmc device into local memory
#) copy the firmware from local memory into the TCM of the Cortex®-M4/7
#) start the firmware from U-Boot with the bootaux command

.. prompt::
   :prompts: U-Boot>

   load mmc ${mmcdev}:1 ${loadaddr} hello_world.bin
   cp.b ${fileaddr} 0x7e0000 0x20000
   bootaux 0x7e0000

.. code-block:: text

   ## Starting auxiliary core stack = 0x20020000, pc = 0x1FFE030D...


"hello world." will be printed on your UART4 terminal window:

.. figure:: images/SDKXpresso-hello-world.png
	:scale: 35 %
	:align: left
	:figwidth: 100%