[U-Boot-Users] Accessing mkimage checksum

[NZG <ngustavson@emacinc.com>]

> Maybe you explain in more detail what you intend to do.
The target board is our SoM-5282M, 
http://www.emacinc.com/som/som5282em.htm
which comes with U-Boot and uClinux installed on it. 
U-Boot has tftp capability and can access all the flash, and is fully capable 
of swapping out the OS image already.
The uClinux build has MTD installed and can see all the external flash of the 
device, which is where the OS image is located.
We want to add a feature to allow the module to reflash it's OS from the 
command line of uClinux through the MTD layer. Ideally, we would like to 
write the image through the MTD layer and then verify it by reading it back 
and making sure the image checksum matches a calculated one.

> I  don't  see 
> why "the flashing utility needs to calculate a checksum" - the uImage
> file  already  has  two  checksums,  so  no new calculation should be
> needed. 
For verification during the writing process.

> If you use the MTD layer as a blockdevice, you will probably  have  a
> file  system  there; then you can just use "cp" as "flashing utility"
> and "mkimage -l" to verify the checksums after writing.
>
> If you use a character device, you can just  use  "cp"  as  "flashing
> utility"  and  "mkimage  -l"  to  verify the checksums after writing;
> probably an additional step will be nedded  to  reead  back  the  MTD
> character  device  in a file, making sure only the original amount of
> data is read back; a tiny shell script based on "ls"  and  "cut"  and
> "dd" will do).
>
> I have no idea what you could need special tools for.
It needs to be an easy to use utility (This utility could be a shell script) 
because we are not the ones using it, it's for the end customer, and further 
down the line, it's for the technicians in the field.
A uClinux daemon that provided a port to do this would be even better.

I realize it's not that complicated an issue, and I could probably figure it 
out in an hour or two. But somebody's probably already done this, why not 
just ask? 

> > This is really a question for both the uClinux and u-boot communities.
> Actually this has nothing to do with uClinux, and  very  little  with
> U-Boot.
It requires a small amount of knowlege of raw access to MTD, the format used 
by mkimage, and it would be nice to know I'm not reinventing the wheel.
Therefore the original question was posted to the uClinux list (for MTD help) 
The U-Boot list (for information about the mkimage format) , and to Wildrice 
(general search for pre-generated scripts and utilities)
I received several helpful responses.
Thank you to everyone who has contributed.

NZG

And there never was an apple, in Adam's opinion, that wasn't worth the trouble 
you got into for eating it.
		-Neil Gaiman