bc10/Software

Summary

This section explains the boot process of bc10. It covers the basic knowledge of the boot process from
turning on the power to starting up the OS. It takes three steps to complete the boot process: bootROM,
X-Loader, and U-Boot. bootROM is factory preconfigured, and this section briefly explains the function
of it. The The detail information of X-Loader and U-Boot is individually published at bc10/x-loader and
bc10/u-boot, respectively.

Boot Sequence

As bc10 (OMAP3530) boots into Linux, the order of the boot sequence in bc10 is described as below. The
boot process starts right after power is turned on.

  1. BootROM
  2. X-Loader
  3. U-Boot
  4. uImage (Linux kernel)

BootROM

OMAP3530 contains BootROM, which includes the code that handles the first boot step. As power is on, because
of the code, BootROM start scanning the devices for the bootloder. BootROM only scans bootable devices and
directly accesses the devices. The devices that BootROM can access and scan the bootloader are listed below.

  • NAND Flash
  • MMC/SD card
  • USB
  • Serial

BootROM looks at the sys_boot pins to determine the order of scanning devices as power is on. As the
setting of the sys_boot pins is rearranged, the order of scanning can be altered.

Scanning Order

bc10 and BeagleBoard have the same configuration for the scanning order. There are two patterns of the scanning
order. While power is turned on (pressing RESET button), the order of scanning can be changed, depending on whether
USER button is pressed or not.

  • USER button is NOT pressed as RESET button is pressed
    • NAND -> USB -> UART -> MMC/SD
  • USER button is pressed as RESET button is pressed
    • USB -> UART -> MMC/SD -> NAND

(Pressing RESET button means that power is turned on.)

If BootROM cannot find the bootloader in one device, then it automatically shifts to the next device and starts
scanning it.

The two sets of the scanning order are very useful and practical. Usually, the bootloders are contained in NAND,
do not be necessary to press USER button. However, in some situations, for example, a new bootloader is tested,
NAND does not work appropriately, or NAND is blank since it is the factory default condition, press USER
button, and access bootloaders in the SD card.

X-Loader

X-Loader is the first bootloader whose objective is to search for U-Boot and to boot it. To search for U-Boot image,
X-Loader access the devices in such order.

  1. MMC/SD card
  2. NAND Flash

For the information of how to build X-Loader from the source code, please visit at bc10/x-loader for the details.

U-Boot

U-Boot is the second bootloader. This is a multifunctional bootloader and capable of booting OS and initializing
hardware. U-Boot is equipped with the command line interface, can access to the file system of MMC/SD, and read
and write in NAND. Since U-Boot is highly functional, any set-up for booting can be handled. For farther information,
please look at bc10/u-boot.

Linux Kernel

Linux kernel image file is named uImage, and uImage can be used for both OpenEmbedded Linux environment and
Android environment. To build Linux kernel (uImage) from source code, please look at bc10/kernel-2.6.32.

Create bootable SD card

Outline

This section explains how to create a bootable SD card, which contains X-Loader and U-Boot. Creating a bootable SD
is the easiest way to boot bc10 since NAND Flash of bc10 is empty when it is shipped from the factory. By the design
of bc10, it cannot be booted from the microSD card slot. bc10 is only booted from the SD card slot. This article
assumes that the OS which U-Boot boot up is Linux and that the SD card becomes a dual-partition card. The first partition
contains the tools for booting, and the second partition has root file system of Linux. The structure of the SD card and
contents of each partition are described as below.

  • FAT32 partition
    • X-Loader
    • U-Boot
    • Linux kernel
  • Linux partition
    • Linux toot file system

It is assumed that working environment is Linux.
The order of the instructions is shown below.

  1. Initialization and setting of partitions
  2. Format the bootlorder file system
  3. Placing the bootlorder files

The instruction is originally listed at LinuxBootDiskFormat (code.google.com), and this section is quoted and rearranged.
For the convenience of the explanation for the command lines, user inputs are also shown, and user inputs are written
inside squire brackets [ ]. This is an example, and the directory and the location of device file may vary. These are
highly dependent on SD cards.

Unmount SD card

Unmount is required for creating partitions and formatting the SD card. If the automounter mounts the SD card, unmount
the SD card.

Assume that presently a SD card is mounted as it is described below.

$ [df -h]
Filesystem            Size  Used Avail Use% Mounted on
...
/dev/sdc1             400M   94M  307M  24% /media/disk
...

The name of the SD card is disk, and the SD card is currently situated the directory /media/disk.
Unmount the SD card.

$ [umount /media/disk]

Initialization and configuration of partitions

Execute fdisk command. The parameter of fdisk is the starting point of the SD card, in which the device file of the SD
card is located. The directory may differ, depending on SD cards. Please check before start this task.

$ [sudo fdisk /dev/sdc]
Command (m for help): [p]

Disk /dev/sdc: 2021 MB, 2021654528 bytes
255 heads, 63 sectors/track, 245 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1   *           1         246     1974240+   c  W95 FAT32 (LBA)
Partition 1 has different physical/logical endings:
     phys=(244, 254, 63) logical=(245, 200, 19)

Write down the number of bytes on the SD card. The number will use later. (in this example 2021654528)
Delete all partitions that already exist in the SD card.

Command (m for help): [d]
Selected partition 1

Change to expert mode.

Command (m for help): [x]

Set the number of heads to 255.

Expert Command (m for help): [h]
Number of heads (1-256, default xxx): [255]

Set the number of sectors to 63.

Expert Command (m for help): [s]
Number of sectors (1-63, default xxx): [63]

The number of cylinders is differ, and it is dependent on SD cards. This is how to calculate the number of cylinders.
The outcome is truncated, do not be rounded.

#cylinders = FLOOR (the number of Bytes on the SD Card (from above) / 255 / 63 / 512 )

The number of cylinders for the SD card used here is calculated as described below.

2021654528 / 255 / 63 / 512 = 245.79
-> 245

Set the number of cylinders, The number of cylinders is 245 for this example.

Expert Command (m for help): [c]
Number of cylinders (1-256, default xxx): [enter the number calculated above]

Return to normal mode.

Expert Command (m for help): [r]

Create FAT32 partition in the SD card.

Command (m for help): [n]
Command action
   e   extended
   p   primary partition (1-4)
[p]
Partition number (1-4): [1]
First cylinder (1-245, default 1): [(press Enter)]
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-245, default 245): [+50]

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))

Set up the boot flag in the first partition, and make it bootable.

Command (m for help): [a]
Partition number (1-4): [1]

Create the second partition for the root file system of Linux.

Command (m for help): [n]
Command action
   e   extended
   p   primary partition (1-4)
[p]
Partition number (1-4): [2]
First cylinder (52-245, default 52): [(press Enter)]
Using default value 52
Last cylinder or +size or +sizeM or +sizeK (52-245, default 245): [(press Enter)]
Using default value 245

Check up configurations of the newly created partitions.

Command (m for help): [p]

Disk /dev/sdc: 2021 MB, 2021654528 bytes
255 heads, 63 sectors/track, 245 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1   *           1          51      409626    c  W95 FAT32 (LBA)
/dev/sdc2              52         245     1558305   83  Linux

Save the changes in the partition table.

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

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table.
The new table will be used at the next reboot.

WARNING: If you have created or modified any DOS 6.x
partitions, please see the fdisk manual page for additional
information.
Syncing disks.

Format the file system

Format the FAT32 partition and the Linux partition.
In the example described below, LABLE1 and LABEL2 are given by the commands. The names of the partitions are
freely decided. Input the names of the partitions.

$ [sudo mkfs.msdos -F 32 /dev/sdc1 -n LABEL1]
mkfs.msdos 2.11 (12 Mar 2005)

$ [sudo mkfs.ext3 -L LABEL2 /dev/sdc2]
mke2fs 1.40-WIP (14-Nov-2006)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
195072 inodes, 389576 blocks
19478 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=402653184
12 block groups
32768 blocks per group, 32768 fragments per group
16256 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: 

Place the image files of bootloaders

The image files of bootloaders are set into the SD card.
First, remount the SD card. (Gently push the SD card into its holder, then the card pops out, and reinsert the
SD card into its folder again.) The mount point of SD card is highly dependent on system. Change the mount point
which is suitable to its system.

X-Loader, the first bootloader, does have strict requirements for its placement on the SD card. Please follow
the direction described below.

  • X-Loader is placed right after formatting FAT32 partition is completed.
  • It places the top directly of the partition.
  • The name of the file is set as MLO.
$ [cp x-load.bin.ift /media/LABEL1/MLO]

Then, U-Boot, the second boot loader, is placed into the SD card.

  • The file name is changed as u-boot.bin.
$ [cp u-boot.bin /media/LABEL1/u-boot.bin]

Place Linux kernel

  • Change the name of Linux kernel image to uImage.
$ [cp uImage /media/LABEL1/uImage]

To make mistakes on the order of placing files and/or in the process of placing a file, the most certain way to
fix the mistakes is to redo from the reformatting the partition of FAT32.

Now, complete the whole process, and unmount the SD card and remove it from the socket.

Boot up from SD card

Insert the SD card in which the bootloaders are installed, into bc10.
Set up the scanning order of BootROM. To put the SD card is higher order than NAND, please press USER button while
power is turned on. bc10 boots up from the SD card.

Reference

Revision History

  • 2010/10/20 This article is originally uploaded
  • 2011/01/14 The information of Linux kernel is added

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Last-modified: 2011-01-14 (Fri) 03:14:29 (2683d)