Specifications

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 interrupted by pressing
any key.
Set this variable to 0 boot 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.
•
bootfile: name of the default image to load with TFTP•
cpuclk: (Only with MPC859 / MPC866 / MPC885 processors) On some processors, the CPU clock
frequency can be adjusted by the user (for example to optimize performance versus power
dissipation). On such systems the cpuclk variable can be set to the desired CPU clock value, in
MHz. If the cpuclk variable exists and its value is within the compile-time defined limits
(CFG_866_CPUCLK_MIN and CFG_866_CPUCLK_MAX = minimum resp. maximum allowed CPU
clock), then the specified value is used. Otherwise, the default CPU clock value is set.
•
ethaddr: Ethernet MAC address for first/only ethernet interface (= eth0 in Linux).
This variable can be set only once (usually during manufacturing of the board). U-Boot refuses to
delete or overwrite this variable once it has been set.
•
eth1addr: Ethernet MAC address for second ethernet interface (= eth1 in Linux).•
eth2addr: Ethernet MAC address for third ethernet interface (= eth2 in Linux).
...
•
initrd_high: used to restrict positioning of initrd ramdisk images:
If this variable is not set, initrd images will be copied to the highest possible address in RAM; this is
usually what you want since it allows for maximum initrd size. If for some reason you want to make
sure that the initrd image is loaded below the CFG_BOOTMAPSZ limit, you can set this environment
variable to a value of "no" or "off" or "0". Alternatively, you can set it to a maximum upper address to
use (U-Boot will still check that it does not overwrite the U-Boot stack and data).
For instance, when you have a system with 16 MB RAM, and want to reserve 4 MB from use by
Linux, you can do this by adding "mem=12M" to the value of the "bootargs" variable. However, now
you must make sure that the initrd image is placed in the first 12 MB as well - this can be done with
•
=> setenv initrd_high 00c00000
Setting initrd_high to the highest possible address in your system (0xFFFFFFFF) prevents U-Boot from
copying the image to RAM at all. This allows for faster boot times, but requires a Linux kernel with zero-copy
ramdisk support.
ipaddr: IP address; needed for tftp command•
loadaddr: Default load address for commands like tftp or loads.•
loads_echo: If set to 1, all characters received during a serial download (using the loads
command) are echoed back. This might be needed by some terminal emulations (like cu), but may as
well just take time on others.
•
mtdparts: This variable (usually defined using the mtdparts command) allows to share a common
MTD partition scheme between U-Boot and the Linux kernel.
•
pram: If the "Protected RAM" feature is enabled in your board's configuration, this variable can be
defined to enable the reservation of such "protected RAM", i. e. RAM which is not overwritten by
•
5.10. U-Boot Environment Variables 80