yosys/tests/simple/dff_init.v

module dff0_test(n1, n1_inv, clk);
  input clk;
  output n1;
  reg n1 = 32'd0;
  output n1_inv;
  always @(posedge clk)
      n1 <= n1_inv;
  assign n1_inv = ~n1;
endmodule

module dff1_test(n1, n1_inv, clk);
  input clk;
  (* init = 32'd1 *)
  output n1;
  reg n1 = 32'd1;
  output n1_inv;
  always @(posedge clk)
      n1 <= n1_inv;
  assign n1_inv = ~n1;
endmodule

module dff0a_test(n1, n1_inv, clk);
  input clk;
  (* init = 32'd0 *) // Must be consistent with reg initialiser below
  output n1;
  reg n1 = 32'd0;
  output n1_inv;
  always @(posedge clk)
      n1 <= n1_inv;
  assign n1_inv = ~n1;
endmodule

module dff1a_test(n1, n1_inv, clk);
  input clk;
  (* init = 32'd1 *) // Must be consistent with reg initialiser below
  output n1;
  reg n1 = 32'd1;
  output n1_inv;
  always @(posedge clk)
      n1 <= n1_inv;
  assign n1_inv = ~n1;
endmodule