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.

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

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

Creating partitions and formatting eMMC

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

The fdisk utility can be used to create partitions on the eMMC.

For example here is the procedure for creating a 128 MB primary partition:

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): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-57024, default 1): Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-57024, default 57024): +128M

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        3907      125016  83 Linux

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table
[  566.062896]  mmcblk0: p1

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:

root@emac-oe:~# mkfs.ext3 /dev/mmcblk0p1
mke2fs 1.41.14 (22-Dec-2010)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
31360 inodes, 125016 blocks
6250 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
16 block groups
8192 blocks per group, 8192 fragments per group
1960 inodes per group
Superblock backups stored on blocks: 
        8193, 24577, 40961, 57345, 73729

Writing inode tables: done      
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 39 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

Formatting a partition with FAT32:

root@emac-oe:~# mkdosfs -F 32 /dev/mmcblk0p1
mkdosfs 2.11 (12 Mar 2005)

Extracting filesystems to eMMC

After formatting a partition correctly, the partition can be mounted and files can be loaded to the eMMC.

For example, here is the procedure for writing a root filesystem to the first partition of an eMMC card:

root@emac-oe:~# mkdir -p /mnt/card
root@emac-oe:~# mount /dev/mmcblk0p1 /mnt/card
root@emac-oe:~# cd /mnt/card
root@emac-oe:~# tar xzvf /images/emac-image.rootfs.tar.gz
    ⋮

Quick Reference (by Target Type)

SoM-3517M

Partitioning the eMMC

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

The partitioning steps are as follows:

1. Create 1st partition (n,p,1,default,+64M)
2. Create 2nd partition (n,p,2,default,default)
3. Change 1st partition type to FAT32 (t,1,c)
4. Make 1st partition ACTIVE (a,1)
5. Write (w)

Formatting the eMMC

root@emac-oe:~# mkfs.ext3 /dev/mmcblk0p2
root@emac-oe:~# mkdosfs -F 32 /dev/mmcblk0p1

Adding Kernel and Bootloader

root@emac-oe:~# mkdir -p /mnt/card
root@emac-oe:~# mount /dev/mmcblk0p1 /mnt/card
root@emac-oe:~# cd /images
root@emac-oe:/images# cp MLO uImage u-boot.bin /mnt/card/
root@emac-oe:/images# sync
root@emac-oe:/images# umount /dev/mmcblk0p1

Extracting Root Filesystem

root@emac-oe:/images# mount /dev/mmcblk0p2 /mnt/card
root@emac-oe:/images# cd /mnt/card
root@emac-oe:/mnt/card# tar xzvf /emac-image.rootfs.tar.gz
root@emac-oe:/mnt/card# cd ..
root@emac-oe:/mnt# sync
root@emac-oe:/mnt# umount /dev/mmcblk0p2