[U-Boot-Users] Special u-boot format for Kernels
Wolfgang Denk
wd at denx.de
Wed Nov 13 20:28:49 CET 2002
Dear Holger,
in message <200211131007.24226.h.schurig at mn-logistik.de> you wrote:
>
> For booting a Linux zImage, you simply jump to it's location (after setting up
> the registers). And you have to set up registers and jump to some extracted
> code anyway, no matter if you if the zImage is already there or if it just
> got extracted out of some mkimage-made image. Setting up the rigth registers
> with the right info is OS dependend anyway.
>
> What is the reason for this, why do you think the image approach is better ---
> or even necessary?
This approach is the result of recurring customer requirements. Our
customers ask:
* How can I identify an image I have stored in flash? Which version
is it? ==> Approach: Name String
* How can I find out when the image was built? ==> Approach: Time
stamp
* How can I make sure an image is OK, i. e. that it was neither
corrupted during download or by erasing / overwriting parts of the
flash where I stroed it? ==> Approach: CRC32 checksum
* How can I make sure I don't try booting a valid image, which is in
fact not a Linux kernel but something else (ramdisk, xxxOS image,
...)? ==> Approach: Tags for OS, type, architecture, etc.
All these issues are required byu many embedded projects where
reliability, software updates etc. play a role. That's why we wrap
the images (Linux kernel, ramdisk, multi-file images, scripts,
firmware, ...) with a special header containing all the required
metadata and checksums.
> Don't read this as a critique, I really don't understand the motivation behind
> this.
There is no technical need for the header if all you want to do is
booting a Linux kernel. But if you have to organize production of
sortware and hardware and set up all the processes for software
updates you will appreciate such mechanisms.
Best regards,
Wolfgang Denk
--
Software Engineering: Embedded and Realtime Systems, Embedded Linux
Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd at denx.de
See us @ electronica 2002 in Munich, Nov 12-15, Hall A3, Booth A3.325
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