[U-Boot] Environment structure.

[Tuma]

Hello All!
I develop some "upgrade" tool based on the U-Boot booted from SD card.
I want to boot from SD card, and execute some simple script which is stored in 
bootcmd environment variable:
"echo Hello! ; mmcinit ; sleep 10 ; reset; " etc...
So I need to generate some environment file. I find source from tools/env very 
useful (I try to get variables from correct file I already have), but I can't 
find any description of environment file (or flash partition) at all (which I 
need to write tool for generating environment file).
Can someone explain me the structure of the file, please.
Something like:
0-4 - CRC
5-... - (Environment)\0(Environment)\0... 
... Environment End Mark...
and so on.

Or tell me in what file should I see from U-Boot source.

And is there any difference between content of OneNAND flash 
environment-partition and file on SD card?

Thank you.

-- 
Software Developer
General Satellite Corp.