Sine Wave generation from triangular wave

module sine_cos(clk, reset, en, sine, cos);
   input clk, reset, en;
   output [7:0] sine,cos;
   reg [7:0] sine_r, cos_r;
   assign      sine = sine_r + {cos_r[7], cos_r[7], cos_r[7], cos_r[7:3]};
   assign      cos  = cos_r - {sine[7], sine[7], sine[7], sine[7:3]};
   always@(posedge clk or negedge reset)
     begin
         if (!reset) begin
             sine_r <= 0;
             cos_r <= 120;
         end else begin
             if (en) begin
                 sine_r <= sine;
                 cos_r <= cos;
             end
         end
     end
endmodule // sine_cos
module pwm_gen(clk,reset_n, pwm_din, pwm_out);
   input   clk, reset_n;
   input [7:0] pwm_din;
   output      pwm_out;
   reg         pwm_out;
   reg [7:0]   pwm_cnt;
   assign      pwm_out_nx = (pwm_cnt <= pwm_din) ? 1'b1 : 1'b0;
   always @(posedge clk or negedge reset_n)
     begin
         if (!reset_n) begin
             pwm_cnt <= 0;
             pwm_out <= 0;
         end else begin
             pwm_cnt <= pwm_cnt + 1'b1;
             pwm_out <= pwm_out_nx; 
         end
     end
   
endmodule
     
module sine_cos_tst();
   reg clk, reset;
   wire [7:0] sine,cos;
   wire        clk_256, pwm_out;
   reg         clk_256_r;
   reg [7:0]   cnt_256;
   sine_cos u1(clk,  reset, clk_256, sine, cos);
   pwm_gen pwm_gen (clk, reset, {~sine[7],sine[6:0]}, pwm_out);
   initial begin
       $shm_open("./WAVEFORM");
       $shm_probe(sine_cos_tst, "AS");
       clk = 0;
       reset = 0;
       cnt_256 = 0;
       clk_256_r = 1'b0;
       #33 reset = 1;
       #2000000 $finish;
   end
   
   always #5 clk = ~clk;
   always @ (posedge clk) begin
       cnt_256 <= cnt_256 + 1;
       clk_256_r <= cnt_256[7];
   end
   assign clk_256 = cnt_256[7] & ~clk_256_r;
   
endmodule