AM335x U-Boot User's Guide
http://processors.wiki.ti.com/index.php/AM335x_U-Boot_User%27s_Guide#Setting_U-Boot_environment_using_uEnv.txt
http://processors.wiki.ti.com/index.php/AM335x_U-Boot_User%27s_Guide#Setting_U-Boot_environment_using_uEnv.txt