Loading Linux Images to a Compact Flash Disk

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When changing firmware images or creating custom firmware images for your Compact Flash-based machine, it is necessary to perform a few steps to load the firmware image onto the CF card.

Necessary Tools

To perform this procedure, you will need to have the following items:

• The Compact Flash card you wish to use to hold the firmware.
• A Compact Flash card reader attached to your computer.
• The firmware image.
• A fully functional Linux desktop.
• The package management tools installed: tar, and either gzip or bzip2 (depending on the image).
• The EMAC package which provides the put-image script. The README.TXT file in the package details out the steps needed to install the script properly.

The put-image script, and its associated tools, can be downloaded from EMAC's Subversion Repository.

The script and its tools can be downloaded, if you have svn (Subversion) installed, by running the following command in a terminal:

svn co https://svn.emacinc.com/public/EMAC-OE-2009.03-STABLE/trunk/contrib/put-image/

When you run the above command, you should see something like this:

developer@ldc:~$ svn co https://svn.emacinc.com/public/EMAC-OE-2009.03-STABLE/trunk/contrib/put-image/

A    put-image/date2stamp
A    put-image/stamp2date
A    put-image/datediff
A    put-image/put-image
A    put-image/lilo-22.8.sbin.static.tgz
A    put-image/README.TXT
Checked out revision 175.

developer@ldc:~$

Procedure

Perform the following steps to load the firmware onto your Compact Flash card:

• Insert the Compact Flash card into your card reader.
• Navigate (from within the shell) to the directory which contains the firmware image you wish to use.
• Determine where the Compact Flash card was mounted:

developer@ldc:~$ dmesg | tail -n 10
[23236.042944] sdc: detected capacity change from 4110188544 to 0
[23243.783467] sd 12:0:0:0: [sdc] 8027712 512-byte logical blocks: (4.11 GB/3.82 GiB)
[23243.785199] sd 12:0:0:0: [sdc] No Caching mode page present
[23243.785204] sd 12:0:0:0: [sdc] Assuming drive cache: write through
[23243.787314] sd 12:0:0:0: [sdc] No Caching mode page present
[23243.787326] sd 12:0:0:0: [sdc] Assuming drive cache: write through
[23243.790625]  sdc: sdc1
[23244.290093] kjournald starting.  Commit interval 5 seconds
[23244.293646] EXT3-fs (sdc1): using internal journal
[23244.293651] EXT3-fs (sdc1): mounted filesystem with ordered data mode
developer@ldc:~$

The output of the dmesg command tells us that the root device node for the Compact Flash card in this case is sdc, and that only partition found is sdc1. Inspect the output shown above to see where this information came from. The /dev/ prefix will go before the device name, but is not shown in the output. The letters you are looking to see will start with either sd or hd. The third letter will specify which of these devices is assigned to the CF Card.

• At this point, it is wise to double check to ensure you have the correct device node for the Compact Flash card. Specifying the wrong device node could cause a complete loss of data on your hard drive. It is very important to be extremely careful when specifying the device node for the Compact Flash.
  
  Continuing with /dev/sdc1 as our example device node, type the following command:

developer@ldc:~$ mount | grep sdc1
/dev/sdc1 on /media/EMAC-OE type ext3 (rw,nosuid,nodev,uhelper=udisks)

This shows us that the device node, /dev/sdc1, is in fact our Compact Flash card. We know this because:

• It is not mounted on one of the standard Linux filesystem mountpoints, such as /, /boot, /usr, or /home.
• It is mounted in the /media directory, where we expect it. We may alternatively expect to see it mounted in /mnt, depending upon the configuration of the Linux distribution in use.

• Use fdisk -l to inspect the device node:

developer@ldc:~$ sudo fdisk -l /dev/sdc
Disk /dev/sdc: 4009 MB, 4009549824 bytes
77 heads, 56 sectors/track, 1816 cylinders, total 7831152 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 identifier: 0x00090707 
  
 Device Boot      Start         End      Blocks   Id  System
/dev/sdc1              62     7831151     3915545   83  Linux
developer@ldc:~$

• The device to specify for the boot argument must also be determined prior to putting the image onto the Compact Flash card. If you downloaded the firmware image from EMAC, there should be a text file associated with the image which tells you which device to specify for this. If you have built your own custom image, you should use the same boot device as you used with firmware from EMAC. In this example, we're using hardware which specifies /dev/hdc for the boot device.
• Now, run the put-image script:

developer@ldc:~$ /path/to/put-image --root=/dev/sdc --boot=/dev/hdc emac-firmware-image.tar.gz

See Also

• Linux Boot Process Customization