[U-Boot] Environment "image" tool

Hi, is there a tool to create an "environemnt image" that I can flash to my NAND?

I think I've seen a tool that takes a text file with an environment setting per line, calculates the CRC and generates a binary that can be transferred to the board (via tftp or other means) to be written with "nand write".

Alternatively, is there a description of how the environment is read, my U-Boot, so that I can write my own program to create such image?

Thanks! bye as