[U-Boot] setting the environment address

[John Stile]

How does uboot decide where in NAND the configuration will be found?
I'm getting the classic errors:
*** Warning - bad CRC or NAND, using default environment

I am writing my environment to nand, with crc, but how do I know that
uboot is looking for it in the right place?

Is that a compile time only setting?
Ultimately I'd like to have 2 copies of the environment.