s0 => s1:  data_in = '1' ;
s0 => s0: ;
s1 => s2:  data_in = '1' ;
s1 => s1: ;
s2 => s3:  data_in = '1' ;
s2 => s2: ;
s3 => s3:  data_in = '1' ;
s3 => s1: ;