Direct boot

The dboot command simplifies operating system bootup by performing the following operations:

Downloads the required files (kernel, flattened device tree, init ramdisk) from the specified media to RAM
Sets the bootargs variable with the boot command line required for the selected operating system
Boots the system

Syntax

'dboot' syntax

=> help dboot - Digi modules boot command

Usage:
dboot <os> [source] [extra-args...]
 Description: Boots <os> via <source>
 Arguments:
   - os:           one of the operating systems reserved names: 
                   linux|android
   - [source]:     tftp|nfs|nand|mmc
   - [extra-args]: extra arguments depending on 'source'

      source=tftp|nfs -> [filename]
       - filename: file to transfer (if not provided, filename will
                   will be taken from variable $zimage)

      source=nand -> [partition] [filename]
       - partition: partition name (if not provided, a partition 
                    with the name of the OS will be assumed)
       - filename: file to transfer (if not provided, filename will
                   will be taken from variable $zimage)

      source=mmc -> [device:part] [filesystem] [filename]
       - device:part: number of device and partition
       - filesystem: fat (default)|ext4
       - filename: file to transfer (if not provided, filename will
                   will be taken from variable $zimage)

Examples

Example 1: Boot Linux from TFTP using kernel image zImage-test

=> dboot linux tftp zImage-test

Example 2: Boot Android from FAT partition 1 on the microSD card (kernel image name is taken by default from variable $zimage):

=> dboot android mmc

Customization of 'dboot' using environment variables

The behavior of the dboot command is highly customizable through its parameters and also using the following environment variables:

Addresses

Variable	Description
$loadaddr	RAM address where the kernel image is downloaded
$fdt_addr	RAM address where the Flattened Device Tree image is downloaded
$initrd_addr	RAM address where the init ramdisk image is downloaded

Image file names

Variable	Description
$zimage	Kernel image filename (or $uimage for systems configured to boot uImage kernel images)
$fdt_file	Flattened Device Tree image filename
$initrd_file	Init ramdisk image filename

Modifiers

Variable	Description
$boot_fdt	Whether the kernel requires a Flattened Device Tree (FDT). Valid values are: yes: FDT is required. If it cannot be downloaded, dboot command will fail. try: FDT is optional. dboot will try to load it but will continue to boot the kernel without it if not available. no: FDT is not required. dboot will not try to download it.
$boot_initrd	Whether the kernel requires an init ramdisk. Valid values are: yes: Init ramdisk is required. If it cannot be downloaded, dboot command will fail. try: Init ramdisk is optional. dboot will try to load it but will continue to boot the kernel without it if not available. no: Init ramdisk is not required. dboot will not try to download it.

Variable

Description

$boot_fdt

Whether the kernel requires a Flattened Device Tree (FDT). Valid values are:

yes: FDT is required. If it cannot be downloaded, dboot command will fail.
try: FDT is optional. dboot will try to load it but will continue to boot the kernel without it if not available.
no: FDT is not required. dboot will not try to download it.

$boot_initrd

Whether the kernel requires an init ramdisk. Valid values are:

yes: Init ramdisk is required. If it cannot be downloaded, dboot command will fail.
try: Init ramdisk is optional. dboot will try to load it but will continue to boot the kernel without it if not available.
no: Init ramdisk is not required. dboot will not try to download it.

Source media

Variable	Description
$mmcdev	Default MMC device index to read files from (when no device index is passed as parameter). U-Boot sets this variable to point to the MMC device index U-Boot has booted from.
$mmcpart	Default MMC partition index to read files from (when no partition index is passed as parameter).

Boot arguments

Variable	Description
$bootargs_android	Contains common Android boot arguments (independent of the media Android is booting from).
$bootargs_mmc_android $bootargs_nand_android $bootargs_tftp_android $bootargs_nfs_android	Scripts that set the $bootargs variable with Android boot arguments when booting from MMC, NAND, TFTP, or NFS, respectively.
$bootargs_mmc_linux $bootargs_nand_linux $bootargs_tftp_linux $bootargs_nfs_linux	Scripts that set the $bootargs variable with Linux boot arguments when booting from MMC, NAND, TFTP, or NFS, respectively.
$rootpath	NFS root path to use in the $bootargs variable when booting from TFTP/NFS.
$mmcroot	Root path to use in the $bootargs variable when booting from MMC.
$mtdrootfsindex	Index number of the MTD partition to use as root file system when booting from NAND.
$bootargs_once	Special variable that is appended to the $bootargs. It can only be set locally with the equals sign, not with the setenv command: => bootargs_once="<arguments>" Locally set variables are not saved across reboots so this will pass boot arguments to the operating system only once.
$extra_bootargs	Placeholder for appending any customized boot arguments at the end of the kernel command line.