[Discuss-gnuradio] how to use the gr_mpsk_receiver_cc

Hi all:
      I want to use the gr_mpsk_receiver_cc block to receive the pi/4 DQPSK  signal. Because it said that
it should use for pi/4 DQPSK.But how should I set the parameter of the block?Did anyone use it to receive
pi/4 DQPSK signal before?