Shutdown the Android OS and PMIC by power button

Hello

         We are designing Android custom device based on AM335xevm_sk kit. We are using Android ICS. 

         We need to shutdown the Android OS and Power management IC by Power button.

        We are using same chip used in SK kit.

       I tried GPIO as POWER button in this case just OS only halted my PMIC not getting turn off. 

      What are the changes need to do for turn of my PMIC from OS.

Thanks 

Kumar