[SOLVED] Preserve RTL dummy register during dc analyze

[phantom1003]

I want to preserve the sram_dummy register here.
So, I tried to use the synopsis directives, it just told me no object called sram_dummy.
I also checked the design after analyze, in gtech unmapped netlist, sram_dummy has been removed.
How can I preserve cell during analyze ?

module mem_ext(
  input W0_clk,
  input [7:0] W0_addr,
  input W0_en,
  input [63:0] W0_data,
  input R0_clk,
  input [7:0] R0_addr,
  input R0_en,
  output [63:0] R0_data
);

  // synopsys dc_script_begin
  // set_dont_touch sram_dummy
  // synopsys dc_script_end
  reg sram_dummy;

  mem256x64 mem0(
  /* output [63:0] */ .Q(R0_data),
  /* input */ .CLK(W0_clk),
  /* input */ .CEN(!(W0_en||R0_en)),
  /* input */ .WEN(!W0_en),
  /* input    [7:0] */ .A(W0_en ? R0_addr : W0_addr),
  /* input    [63:0] */ .D(W0_data)
  );

endmodule

 

[FvM]

To preserve a register, it must at least exist in the RTL description. But there's no register sram_dummy connected somehow in the shown module.

 

[phantom1003]

To preserve a register, it must at least exist in the RTL description. But there's no register sram_dummy connected somehow in the shown module.

Does the definition regsramdummy; regsramdummy; is enough?
Must I instantiate a FF module?

 

[ThisIsNotSam]

you need to at least reference the register somewhere, otherwise it is useless logic.