Using idle task which created by scheduler to reduce power consumption:
-in idle task need add code to adjust CPU sys-clock & time-tick
-in scheduler need ass code to recovery CPU sys-clock & time-tick before task is entering “running” state.
Please comment my above design concepts, thanks.
Look forward to receiving your comments soon.
Michael

You can do this using the tickless idle mode, which includes pre and post sleep macros.  You can use the pre and post sleep macros to perform any application specific processing that is necessary.  See the link below.
http://www.freertos.org/low-power-tickless-rtos.html Regards.