[U-Boot-Users] Special u-boot format for Kernels

[Wolfgang Denk]

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
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