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.

    Target (Linux)
    fdisk -l

    Note

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

    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*”.

Target (Linux)
mount | grep mmc
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.

    Target (Linux)
    ls /run/media/mmcblk0p2
    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.

    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.

    Target (Linux)
    cp ~/test.txt /run/media/mmcblk0p2

  • Verify that the file was written to the eMMC.

    Target (Linux)
    ls /run/media/mmcblk0p2
    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.

    Target (Linux)
    md5sum ~/test.txt
md5sum /run/media/mmcblk0p2/test.txt
    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.

    Target (Linux)
    cp /run/media/mmcblk0p2/test.txt ~/test-READ.txt

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

    Target (Linux)
    md5sum /run/media/mmcblk0p2/test.txt
md5sum ~/test-READ.txt
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 eMMC guide.