Loading Images onto eMMC Devices
Contents
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.
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:
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
