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11.1. U-Boot Tips and Tricks: preboot, update, etc.

preboot
This variable can be used to run specific code before the normal startup (i.e. CONFIG_BOOTDELAY loop, autostart or interactive mode) begins. This is especially useful when its contents are generated automatically, i.e. by checking for keypresses, etc.

update
[todo: explain update procedures using U-Boot]

Loading Compressed Images
Sometimes you may want to store some data in compressed format (for example to save flash memory), while your application needs the data in uncompressed form. You can trick U-Boot to do this uncompressing like this:

Generate a compressed U-Boot image of type "standalone" (="mkimage ... -T standalone -C gzip ..."=) and make sure that the envrionment variable autostart is set to no (i. e. enter "setenv autostart no;saveenv"). If you then use "bootm" for such an image, U-Boot will uncompress the contents of the image and store it at the "load address" ("-a" option for mkimage), but not attempt to start it yet. If the image contains executable code, you can omit the setting of "autostart", and U-Boot will automagically start the image by jumping to the entry point address ("-e" option for mkimage).
11. The powerful U-Boot command line interface 1. Embedded Linux Training course 12. Build, configuration of the Linux kernel, more details
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