There seem to be a lot of differences in the different plug types and versions of U-Boot.
On my SheevaPlug with U-Boot 2011.06 (Jul 03 2011 - 02:54:01), there is an "env" command:
Marvell>> ? env
env - environment handling commands
env default -f - reset default environment
env edit name - edit environment variable
env export [-t | -b | -c] addr [size] - export environment
env import [-d] [-t | -b | -c] addr [size] - import environment
env print [name ...] - print environment
env run var [...] - run commands in an environment variable
env save - save environment
env set [-f] name [arg ...]
I tried using it when I was getting some wierd behavior.I am sorry I didn't keep a copy of it.But one thing I have always wondered was what all those "x_bootargs*" and "x_bootcmd*" settings were for. I didn't get an answer but I noticed that they were all re-created.
Now, I cannot boot the onboard nand. So I missed something in my boot sequence. Uimage and uinitrd seem to load and verify ok but it hangs on booting the kernel.
But the good news is that my new Debian testing version on an SD seems to work fine so far:
This is Debian 7.0, "Wheezy", "Linux debian 3.2.0-4-kirkwood #1 Debian 3.2.35-2 armv5tel GNU/Linux".