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With the
autoscr command you can run "shell" scripts
under U-Boot: You create a U-Boot script image by simply writing
the commands you want to run into a text file; then you will have to
use the
mkimage tool to convert this text file
into a U-Boot image (using the image type
script).
This image can be loaded like any other image file, and with
autoscr you can run the commands in such an image.
For instance, the following text file:
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can be converted into a U-Boot script image using the
mkimage command like this:
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Now you can load and execute this script image in U-Boot:
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=> help bootm
bootm - boot application image from memory
Usage:
bootm [addr [arg ...]]
- boot application image stored in memory
passing arguments 'arg ...'; when booting a Linux kernel,
'arg' can be the address of an initrd image
When booting a Linux kernel which requires a flat device-tree
a third argument is required which is the address of the
device-tree blob. To boot that kernel without an initrd image,
use a '-' for the second argument. If you do not pass a third
a bd_info struct will be passed instead
Sub-commands to do part of the bootm sequence. The sub-commands must be
issued in the order below (it's ok to not issue all sub-commands):
start [addr [arg ...]]
loados - load OS image
ramdisk - relocate initrd, set env initrd_start/initrd_end
fdt - relocate flat device tree
cmdline - OS specific command line processing/setup
bdt - OS specific bd_t processing
prep - OS specific prep before relocation or go
go - start OS
=>
The
bootm command is used to start operating system
images. From the image header it gets information about the type of
the operating system, the file compression method used (if any), the
load and entry point addresses, etc. The command will then load the
image to the required memory address, uncompressing it on the fly if
necessary. Depending on the OS it will pass the required boot
arguments and start the OS at it's entry point.
The first argument to
bootm is the memory address
(in RAM, ROM or flash memory) where the image is stored, followed by
optional arguments that depend on the OS.
Linux requires the flattened device tree blob to be passed at boot time, and
bootm expects its third argument to be the address of the blob in memory. Second argument to
bootm depens on whether an
initrd initial ramdisk image is to be used. If the kernel should be booted without the initial ramdisk, the second argument should be given as "-", otherwise it is interpreted as the start address of
initrd (in RAM, ROM or flash memory).
To boot a Linux kernel image without a
initrd
ramdisk image, the following command can be used:
=> bootm ${kernel_addr} - ${fdt_addr}
If a ramdisk image shall be used, you can type:
=> bootm ${kernel_addr} ${ramdisk_addr} ${fdt_addr}
Both examples of course imply that the variables used are set to correct
addresses for a kernel, fdt blob and a
initrd ramdisk image.
When booting images that have been loaded to RAM (for instance
using
TFTP download) you have to be careful that the locations where
the (compressed) images were stored do not overlap with the memory
needed to load the uncompressed kernel. For instance, if you load a
ramdisk image at a location in low memory, it may be overwritten when
the Linux kernel gets loaded. This will cause undefined system
crashes.
=> help go
go - start application at address 'addr'
Usage:
go addr [arg ...]
- start application at address 'addr'
passing 'arg' as arguments
=>
U-Boot has support for so-called
standalone applications.
These are programs that do not require the
complex environment of an operating system to run. Instead they can
be loaded and executed by U-Boot directly, utilizing U-Boot's
service functions like console I/O or
malloc()
and
free().
This can be used to dynamically load and run special extensions to
U-Boot like special hardware test routines or bootstrap code to load
an OS image from some filesystem.
The
go command is used to start such standalone
applications. The optional arguments are passed to the application
without modification. For more informatoin see
5.12. U-Boot Standalone Applications.
