eMMC
=====

This guide will show how to view partition information, read from, and write to the eMMC featured on the phyCORE-i.MX8X SOM.

.. note:: In order to follow this guide your phyCORE-i.MX8X development kit must be booting from SD Card.


Viewing Available eMMC Partitions
----------------------------------

* You can verify the eMMC partitions by using the following command to list the partition information of known MMC devices. The 'fdisk' utility is a very powerful tool which you can use to manage the partitions on a particular flash device.

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

    fdisk -l

  .. note::  The eMMC corresponds to /dev/mmcblk0 and the SD Card is /dev/mmcblk1 in the output.

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

    Disk /dev/mtdblock0: 64 MiB, 67108864 bytes, 131072 sectors
    Units: sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes


    Disk /dev/mmcblk0: 7.1 GiB, 7616856064 bytes, 14876672 sectors
    Units: sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disklabel type: dos
    Disk identifier: 0x539985d3

    Device         Boot  Start     End Sectors  Size Id Type
    /dev/mmcblk0p1 *     16384  186775  170392 83.2M  c W95 FAT32 (LBA)
    /dev/mmcblk0p2      196608 7480935 7284328  3.5G 83 Linux


    Disk /dev/mmcblk1: 14.86 GiB, 15931539456 bytes, 31116288 sectors
    Units: sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disklabel type: dos
    Disk identifier: 0x539985d3

    Device         Boot   Start      End  Sectors  Size Id Type
    /dev/mmcblk1p1 *      16384   186775   170392 83.2M  c W95 FAT32 (LBA)
    /dev/mmcblk1p2       196608  7480935  7284328  3.5G 83 Linux
    /dev/mmcblk1p3      7481344 31115263 23633920 11.3G  b W95 FAT32


.. warning:: Be careful using the "fdisk" command. If you aren't careful, it can easily delete a partition of a flash device you didn't intend to, and this could be your root filesystem!


Mounting the eMMC
------------------

* The flash devices are mounted by default and you can verify their mount points with the following command.

  .. note:: The eMMC partitions are mounted as "mmcblk0p1" and "mmcblk0p2" respectively. The SD card partitions are mounted as "mmcblk1p*".

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

    mount | grep mmc

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

   /dev/mmcblk1p2 on / type ext4 (rw,relatime)
   /dev/mmcblk0p1 on /run/media/mmcblk0p1 type vfat (rw,relatime,gid=6,fmask=0007,dmask=0007,allow_utime=0020,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
   /dev/mmcblk0p2 on /run/media/mmcblk0p2 type ext4 (rw,relatime)
   /dev/mmcblk1p1 on /run/media/mmcblk1p1 type vfat (rw,relatime,gid=6,fmask=0007,dmask=0007,allow_utime=0020,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
   /dev/mmcblk1p3 on /run/media/mmcblk1p3 type vfat (rw,relatime,gid=6,fmask=0007,dmask=0007,allow_utime=0020,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)

* Check the contents of the eMMC's partition by entering the following.

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

    ls /run/media/mmcblk0p2

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

    bin   dev  home  lost+found  mnt  proc  sbin  tmp         usr
    boot  etc  lib   media       opt  run   sys   unit_tests  var

Write to eMMC
----------------

* Create a test file.

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

    echo "Hello World" > ~/test.txt

* Now you can use the copy (cp) or move (mv) commands to put this file on the eMMC.

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

    cp ~/test.txt /run/media/mmcblk0p2

* Verify that the file was written to the eMMC.

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

    ls /run/media/mmcblk0p2

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

    bin   dev  home  lost+found  mnt  proc  sbin  test.txt  unit_tests  var
    boot  etc  lib   media       opt  run   sys   tmp       usr

* Make sure the file was not corrupted during the transfer using md5sum.

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

    md5sum ~/test.txt
    md5sum /run/media/mmcblk0p2/test.txt

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

    e59ff97941044f85df5297e1c302d260  /home/root/test.txt
    e59ff97941044f85df5297e1c302d260  /run/media/mmcblk0p2/test.txt

Reading from eMMC
------------------

* Use the copy (cp) or move (mv) command to put this file back onto your SD card.

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

    cp /run/media/mmcblk0p2/test.txt ~/test-READ.txt

* Make sure the file was not corrupted during the transfer using md5sum.

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

    md5sum /run/media/mmcblk0p2/test.txt
    md5sum ~/test-READ.txt

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

    e59ff97941044f85df5297e1c302d260  /run/media/mmcblk0p2/test.txt
    e59ff97941044f85df5297e1c302d260  /home/root/test-READ.txt

Booting from eMMC
-------------------

To learn more about booting from eMMC, checkout the flashing :ref:`flasheMMC-8x` guide.