Kontron AM4904, User Manual

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Operating the Unit
81 AM4904 User Guide
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3.6.2 Bootloader shell and options
The boot process can be interrupted by entering the bootstopphrase "stop". Enter the string on the serial
console when the 'type configured bootstopkey to abort' message appears on the screen. This will open a
bootloader shell session.
“?” provides a list of possible commands, “printenv” provides a list of environment settings.
The bootloader shell can be used to customize boot options and system startup.
For additional information about customization of u-boot, please refer to the u-boot webpage:
http://sourceforge.net/projects/u-boot/
Table 3-37: Bootloader Environment Variables
Name Description
ethaddr
Contains the default base MAC address of the board. If this is not set, the MAC address
from VPD is used.
bootcmd
This variable defines a command string that is automatically executed when the ini-
tial countdown is not interrupted.
This command is only executed when the variable bootdelay is also defined!
bootcmdflash
Contains the standard startup script for loading OS image from flash partition com-
mand. This will load the Linux kernel and start it with a CRAMFS (TBC, maybe INITRD)
type root file system.
bootcmdnet Contains the standard startup script for loading OS image from network
bootcmdprd Contains the standard startup script for use during board production
bootcmdrecover Contains standard startup script for board firmware recovery in boot firmware
bootdelay
After reset, U-Boot will wait this number of seconds before it executes the contents of
the bootcmd variable. During this time a countdown is printed, which can be inter-
rupted by pressing any key.
Set this variable to 0 boots without delay. Be careful: depending on the contents of
your bootcmd variable, this can prevent you from entering interactive commands
again forever!
Set this variable to -1 to disable autoboot.
Default: 3 for flash based bootloader, -1 for RAM resident bootloader
bootsource
When the standard boot sequence is used, contains the boot source, either flash, net,
prd to select the respective boot sequence to activate. It is only used when bootcmd
contains the default startup script, which may be overridden by the user.
default: flash
ethact
Default network interface used by network commands (bootp, tftpboot et al)
default: ppc_4xx_eth0
loadaddr
Default load address for network transfers. This is used as a temporary storage for
netbooting and firmware updates.
default: 0x08000000
clear_env
Command script (use with “run clear_env”) that erases the U-Boot environment for
the active image
clear_config Erase config partition to restore factory defaults for Linux BSP settings.
flash_update
Command script to flash a Linux kernel and rootfs image transferred with tftpboot to
the active Linux kernel and rootfs partition