BBB angstrom kernel 3.8 sleep mode suspend to ram

Hi

Right now I am using BBB to construct a platform and facing a problem that I can’t not make the BBB to sleep mode like “echo mem > /sys/power/state”. My BBB’s linux is angstrom 3.8. I know that TI AM335x SDK could set BBB to sleep mode, but I try it on angstrom, my BBB could not.

Have anyone encounter this problem before and how to solve it?

Thanks !

Dan