In order to create a bootable microSD compatible with the OMAP3 boot ROM you must set a special geometry using the fdisk "Expert mode".
This example will show the steps for setting up a brand new 2Gb microSD card.
First insert your card into your development machine's flash card slot. You may need to use a microSD to SD card adaptor to fit your slot.
On my Ubuntu 8.04 machine, the newly inserted card shows up as /dev/sde and that is the device name that will be used through this example. You should substitute the proper device name for your machine. You can use 'mount' or 'df' to see where the card mounts on your machine.
Let's unmount the device's existing file system before we get started with fdisk:
$ sudo umount /dev/sde1
Now launch fdisk and create an empty partition table. Note that the argument for fdisk is the entire device (/dev/sde) not just a single partition (i.e. /dev/sde1):
# sudo fdisk /dev/sde Command (m for help): o Building a new DOS disklabel. Changes will remain in memory only, until you decide to write them. After that, of course, the previous content won't be recoverable. Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
Let's first look at the current card information:
Command (m for help): p Disk /dev/sde: 2032 MB, 2032664576 bytes 64 heads, 63 sectors/track, 984 cylinders Units = cylinders of 4032 * 512 = 2064384 bytes Disk identifier: 0x00aa8e5c Device Boot Start End Blocks Id System
Note the card size in bytes. We will needed it later in the process.
Now go into "Expert" mode:
Command (m for help): x
Next we will set the geometry to 255 heads, 63 sectors and a calculated value for the number of cylinders required for the particular microSD card.
To calculate the number of cylinders, we take the 2032664576 bytes reported above by fdisk divided by 255 heads, 63 sectors and 512 bytes per sector:
2032664576 / 255 / 63 / 512 = 247.12 which we round down to 247 cylinders.
Expert command (m for help): h Number of heads (1-256, default 4): 255 Expert command (m for help): s Number of sectors (1-63, default 62): 63 Warning: setting sector offset for DOS compatiblity Expert command (m for help): c Number of cylinders (1-1048576, default 984): 247
Return to fdisk's main mode and create a new partition 32 MB FAT partition:
Expert command (m for help): r Command (m for help): n Command action e extended p primary partition (1-4) p Partition number (1-4): 1 First cylinder (1-247, default 1): 1 Last cylinder or +size or +sizeM or +sizeK (1-247, default 15): +32M
Change the partition type to FAT32:
Command (m for help): t Selected partition 1 Hex code (type L to list codes): c Changed system type of partition 1 to c (W95 FAT32 (LBA))
And mark it bootable:
Command (m for help): a Partition number (1-4): 1
Next we create an ext3 partition for the rootfs:
Command (m for help): n Command action e extended p primary partition (1-4) p Partition number (1-4): 2 First cylinder (6-247, default 6): 6 Last cylinder or +size or +sizeM or +sizeK (6-247, default 247): 247
To verify our work, lets print the partition info:
Command (m for help): p Disk /dev/sde: 2032 MB, 2032664576 bytes 255 heads, 63 sectors/track, 247 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x00aa8e5c Device Boot Start End Blocks Id System /dev/sde1 * 1 5 40131 c W95 FAT32 (LBA) /dev/sde2 6 247 1943865 83 Linux
Up to this point no changes have been made to the card itself, so our final step is to write the new partition table to the card and then exit:
Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. WARNING: If you have created or modified any DOS 6.x partitions, please see the fdisk manual page for additional information. Syncing disks.
We format the first partition as a FAT file system (the -n parameter gives it a label of FAT, you can change or omit this if you like):
# sudo mkfs.vfat -F 32 /dev/sde1 -n FAT mkfs.vfat 2.11 (12 Mar 2005)
We format the second partition as an ext3 file system:
$ sudo mkfs.ext3 /dev/sde2 mke2fs 1.40.8 (13-Mar-2008) Filesystem label= OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) 121920 inodes, 485966 blocks 24298 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=499122176 15 block groups 32768 blocks per group, 32768 fragments per group 8128 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912 Writing inode tables: done Creating journal (8192 blocks): done Writing superblocks and filesystem accounting information: ^[done This filesystem will be automatically checked every 36 mounts or 180 days, whichever comes first. Use tune2fs -c or -i to override.
There are three files required on the first (FAT) partition to boot your Overo:
You can build these yourself or download pre-built images. It is important that these three files have precisely these names.
Once you have completed building or downloading these files, mount the FAT partition of your microSD card. This example will assume that you have mounted it at /media/card:
sudo mount /dev/sde1 /media/card
Due to constraints of the mask boot ROM in the OMAP processor, MLO should be written first:
$ sudo cp MLO-overo /media/card/MLO
Then copy u-boot and the linux kernel to the card:
$ sudo cp u-boot-overo.bin /media/card/u-boot.bin $ sudo cp uImage-overo.bin /media/card/uImage
You can now unmount the FAT partition:
$ sudo umount /dev/sde1
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