Loading Images onto eMMC Devices

TODO: {{#todo:InProgress|Michael Welling|oe 4,oe 5,mw,InProgress}}

Background

Newer EMAC products have started using eMMC in place of NAND flash. eMMC is an embedded MMC compliant memory that takes the form of an integrated circuit instead of a media card.

For more information about MMC see the following page: http://en.wikipedia.org/wiki/MultiMediaCard

U-Boot does not support writing to file systems in eMMC. To overcome this issue, the embedded target has to be boot into Linux using an auxiliary method. Once U-Boot has been loaded into RAM, it can be used to load the target kernel using TFTP and boot into a file system stored in NFS. Once the board has boot into Linux the eMMC can be partitioned, formatted, and the root file system can be extracted. The SoM-3517M requires a special FAT formatted partition that contains the bootloader and Linux kernel images. This article explains the general process of writing the eMMC from Linux as well as some specifics related to the programming the SoM-3517M.

The procedures below require that you have a TFTP and NFS server setup on a host computer.

For instructions on setting up a TFTP server see the following page: Installing TFTP server

For installation of a bootable NFS see the following page: Setting up an NFS File Server

For instruction for booting into NFS with U-Boot: Booting with an NFS Root Filesystem

Creating partitions and formatting eMMC

Once the Linux command prompt is reached the Linux utilities can be used to create and format partitions. The fdisk utility can be used to create partitions on the eMMC.

root@emac-oe:~# fdisk /dev/mmcblk0

The number of cylinders for this disk is set to 57024.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)
 
Command (m for help): p
  Disk /dev/mmcblk0: 1868 MB, 1868562432 bytes
4 heads, 16 sectors/track, 57024 cylinders
Units = cylinders of 64 * 512 = 32768 bytes
         Device Boot      Start         End      Blocks  Id System
/dev/mmcblk0p1   *           1        1954       62520   c Win95 FAT32 (LBA)
/dev/mmcblk0p2            1955       57024     1762240  83 Linux
 Command (m for help): q

For more information about fdisk http://tldp.org/HOWTO/Partition/fdisk_partitioning.html

After creating the partitions they can formatted with the various mkfs utilities.

Formatting a partition with EXT3:

mkfs.ext /dev/mmcblk0p2

Formatting a partition with FAT32:

mkdosfs -F 32 /dev/mmcblk0p1

Extracting filesystems to eMMC

mount /dev/mmcblk0p2 /mnt/card
cd /mnt/card
tar xzvf /emac-image.rootfs.tar.gz

Quick Reference (by Target Type)

SoM-3517M

mkdosfs -F 32 /dev/mmcblk0p1
mount /dev/mmcblk0p1 /mnt/card
cd /vg-controls
cp MLO uImage u-boot.bin /mnt/card/
sync
umount /dev/mmcblk0p1 mkfs.ext3 /dev/mmcblk0p2
mount /dev/mmcblk0p2 /mnt/card
cd /mnt/card
tar xzvf /emac-image-som3517-20120530221838.rootfs.tar.gz
cd ..
sync
umount /dev/mmcblk0p2