> setenv selftest-#megs 64

You can also just set that to a large number like 512, and it will
automatically (well, on every machine I've tried it on) clip to the
actual amount of memory in the machine.

> And the next time the machine is reset or powered on (or boots, i
> think) it will test that much RAM.

Reset, yes, including power-on reset (but not including the reset
inherent in rebooting on ROMs that include a reset in their reboot
sequence).  Boots, no, at least not unless you boot an OS that checks
the variable and tests memory itself.  At least, I've never seen a
machine retest memory when it's rebooted without being reset.

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