User manual

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U-Boot for MPL SBC

User Manual

 2003 by MPL AG

MEH-10082-002 Rev. D

High-Tech • Made in Switzerland

3.4 U-Boot Environment Variables

One of the powerful features of the U-Boot are the environment variables. They are stored in the on board EEPROM and

protected with a CRC32 checksum. These variables are used to store the board properties and control the boot behavior.

3.4.1 Board properties Variables

Two variables are set during manufacturing, and are neither erasable nor over-write-able:

serial#

contains the Board name and the serial number for example: MIP405_100

ethaddr

contains the MAC address of the ethernet port.

3.4.2 Variables controlling the OS boot

Following variables are used to control the boot process of the operating system:

bootargs

contains the boot arguments which will be transferred to the kernel.

bootcmd

contains the commands with which the operating system is loaded and booted. This variable will be executed if

invoking the command ‘bootd’ or the bootdelay as expired.

bootdelay

contains the number seconds u-boot waits, before executing the variable ‘bootcmd’. If set to ‘0’ u-boot starts

immediately. If set to a negative number, u-boot does not boot the operating system and prompt the user for

input.

3.4.3 Variables for U-Boot behavior

Following variables changes the behavior of the u-boot:

baudrate

contains the baudrate of the serial console. Please note that this number is decimal. If not defined, the baudrate

of the serial line is 9600.

loads_echo

Set this variable to ‘1’ if your terminal program requires an echo of the sent data. This is only used in

conjunction with the command ‘loadb’.

preboot

contains commands which will be executed before u-boot prompts.

loadaddr

contains the load address where the image from ‘tftpboot’ or ‘loadb’ is stored.

autostart

Set to ‘yes’ if the image should automatically started after it is load.

3.4.4 Network Variables

Following variables are used for network properties:

bootfile

contains the default name of the file which will be retrieved during tftpboot.

ipaddr

contains the IP address of the board.

serverip

contains the IP address of the TFTP server.

autoload

used to decide if the commands ‘dhcp’, ‘rarpb’ or ‘bootp’ should also load the image via tftp. If set to ‘no’ the

image will not be loaded.