anchor.diff:  import DefaultValue::*;
   
   interface DiffOut;
  -   method Action _write(Bit#(1) v);
      method Bit#(1) read_p();
      method Bit#(1) read_n();
   endinterface 
  
positive.code:    path(I, O);
     path(I, OB);
  
    schedule _write  SB (read_p, read_n);
    schedule _write C _write;
    schedule (read_p, read_n) CF (read_p, read_n);
  
  endmodule: mkxOBUFDS
  
negative.code:    
     interface PipeIn dac;
     
        method Action enq(Vector#(2, OIQ) v);
  	 outfifo.enq(v);
        endmethod
        
  