anchor.diff:        oreg <= svalue[0];
      endmethod
      
  -   interface r = dreg;
  +   interface r = ?;
      interface tdo = regToReadOnly(oreg);
         
   endmodule
  
positive.code: module mkReadOnlyJtagReg#(a v)(JtagReg#(a))
     provisos(Bits#(a,asize), Add#(1,__a,asize));
     
     Reg#(a) dreg <- mkReg(v);
     Reg#(a) sreg <- mkReg(?);
     Reg#(bit) oreg <- mkReg(?);
     
  
negative.code:    endmethod
  
     method Action capture ();
        sreg <= v;
     endmethod
     
     method Action shift (bit d);
  