module clk_div (
    clk_in,
    reset,
    e,
    div,
    clk_out
);
input   clk_in;
input   reset;
input   e;
input[31:0] div;
output  clk_out;
wire[31:0] M;
wire clk_out_odd ;
reg clk_out_even;
      
// bit_of_N: N_odd的二進制位寬
reg [31:0] cnt_p; // 上升沿計數單位
reg [31:0] cnt_n; // 下降沿計數單位
reg [31:0] count;
reg clk_p; // 上升沿時鐘
reg clk_n; // 下降沿時鐘

assign M = (div>>1'b1); 
assign clk_out_odd = (clk_n & clk_p); // 按位與(作用:掩碼)
assign clk_out = (e==0) ? clk_in : div[0:0] ? (~clk_out_odd) : clk_out_even; // 按位與(作用:掩碼) 
// 上升沿計數器: 0~(div)
always @ (posedge clk_in or posedge reset)
	begin
	  if (reset)
		cnt_p <= 0;
	  else
	  begin
		if (cnt_p == (div-32'b1))
		  cnt_p <= 0;
		else
		  cnt_p <= cnt_p + 32'b1;
	  end
	end
 
// 生成上升沿時鐘
// 0~(N>>1) ↑ -> 1; ((N/2)+1)~(div) ↑ -> 0
always @ (posedge clk_in or posedge reset)
	begin
	  if (reset)
		clk_p <= 0;
	  else
	  begin
		if (cnt_p <= M) // 0 ~ (N/2)
		  clk_p <= 1;
		else 
		  clk_p <= 0;
	  end
	end
 
 
// 下降沿計數器: 0~(div)
always @ (negedge clk_in or posedge reset)
	begin
	  if (reset)
		cnt_n <= 0;
	  else
	  begin
		if (cnt_n == (div-32'b1))
		  cnt_n <= 0;
		else
		  cnt_n <= cnt_n + 32'b1;
	  end
	end
 
// 生成下降沿時鐘
// 0~(N>>1) ↓ -> 1; ((N/2)+1)~(div) ↓ -> 0
always @ (negedge clk_in or posedge reset)
	begin
	  if (reset)
		clk_n <= 0;
	  else
	  begin
		if (cnt_n <= M) // 0 ~ (N/2)
		  clk_n <= 1;
		else 
		  clk_n <= 0;
	  end
	end
//============================================================
  always @(posedge clk_in or posedge reset)
    begin
      if(reset)
        begin
          count=32'd1;
          clk_out_even=0;
        end
      else
      begin
		if(count==(div>>1'b1))
		  begin
		    count=32'd1;
		    clk_out_even=~clk_out_even;
		  end
		else
		  count=count+32'd1;
	  end
   end 
endmodule