Be careful: depending on the contents of your bootcmd variable, this can prevent you from entering interactive commands again forever! Set this variable to 0 boot without delay. During this time a countdown is printed, which can be interrupted by pressing any key. This command is only executed when the variable bootdelay is also defined!Īfter reset, U-Boot will wait this number of seconds before it executes the contents of the bootcmd variable. This variable defines a command string that is automatically executed when the initial countdown is not interrupted. The contents of this variable are passed to the Linux kernel as boot arguments (aka “command line”). If set to yes, an image loaded using the rarpb, bootp, dhcp, tftp, disk, or docb commands will be automatically started (by internally calling the bootm command).Ī decimal number that selects the console baudrate (in bps). If set to no (or any string beginning with 'n'), the rarpb, bootp or dhcp commands will perform only a configuration lookup from the BOOTP / DHCP server, but not try to load any image using TFTP. The location on the flash partition is predefined:
package/uboot-ar71xx/files/include/configs/nbg460n.h for the Zyxel NBG 460N/550N/550NH. The environment variables are set up in a board specific file, e.g. The environment is usually at the end of the uboot partition. This flexibility is based on being able to easily change environment variables. One of the huge advantages of Das U-Boot is its ability for run time configuration.
#U boot configuration serial
You can read and write these values when you are connected to the U-Boot console via Serial Port and also from the CLI once you booted OpenWrt. It stores some values like the IP address of the TFTP server (on your PC) to which the the TFTP client (part of U-Boot) will try to connect, etc. This can hardly be compared to NVRAM/TFFS-approach of other bootloaders. The source of these values can be found in the UBIFS NAND boot Wiki page.Das U-Boot uses a small amount of space on the flash storage usually on the same partition it is stored on to store some important configuration parameters. It will default to 1, the only amount supported by the 335x U-Boot. All NAND sizes use a blank "Number of Sectors" field.The "Flash Sector Size" depends on the NAND size:.All NAND sizes use a 0x20000 byte "Env.All NAND sizes use /dev/mtd6 "Device Name" with a 0x0000 "Device Offset.".These settings may need to change based on the amount of NAND installed on your MitySOM-335x module: For a 512MB NAND module, /etc/fw_env.config should appear as follows: ~/u-boot-mityarm-335x> scp tools/env/fw_printenv /etc/fw_env.config file will need to be created to tell fw_printenv where to find the U-Boot configuration. ~/u-boot-mityarm-335x> make HOSTCC=arm-arago-linux-gnueabi-gcc env To build the fw_printenv tool, build the env target and transfer the program to the device: U-Boot also includes a utility to inspect the installed environment, fw_printenv, located in tools/env. Reading the U-Boot configuration stored in NAND ¶ The U-Boot Env is stored in NAND partition 6 for every MitySOM-335x configuration as explained in the UBIFS NAND boot Wiki page. To write the uEnv.dat file to NAND, copy it to the target board and run: This will create a uEnv.dat file from a uEnv.txt file. Tools/mkenvimage -s 131072 -o ~/uEnv.dat ~/uEnv.txt To use the tool, first save the U-Boot configuration file, then invoke mkenvimage as follows: After building U-Boot, the utility is located at tools/mkenvimage. The U-Boot source includes a utility called mkenvimage that will prepare a U-Boot configuration for nandwrite.
Writing the U-Boot configuration stored in NAND ¶ To view or change this file from Linux, mount the boot partition and edit the file with a text editor. When booting from MMC, the U-Boot configuration is loaded from a file called uEnv.txt on the boot partition. Configure U-Boot from Linux ¶ Updating the U-Boot configuration stored on SD card ¶
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