8-3优先编码器

module coder_83(
  input [7:0] data_in,
  input en_in_n,
  output reg [2:0] code_out,
  output reg en_out,
  output reg state
);

always@(en_in_n or data_in) begin
  if(en_in_n) begin
    code_out <= 3‘b111;
    en_out <= 1;
    state <= 1;
  end
  else if (data_in[7] == 0) begin
    code_out <= 3‘b000;
    en_out <= 1;
    state <= 0;
  end
  else if (data_in[6] == 0) begin
    code_out <= 3‘b001;
    en_out <= 1;
    state <= 0;
  end
  else if (data_in[5] == 0) begin
    code_out <= 3‘b010;
    en_out <= 1;
    state <= 0;
  end
  else if (data_in[4] == 0) begin
    code_out <= 3‘b011;
    en_out <= 1;
    state <= 0;
  end
  else if (data_in[3] == 0) begin
    code_out <= 3‘b100;
    en_out <= 1;
    state <= 0;
  end
  else if (data_in[2] == 0) begin
    code_out <= 3‘b101;
    en_out <= 1;
    state <= 0;
  end
  else if (data_in[1] == 0) begin
    code_out <= 3‘b110;
    en_out <= 1;
    state <= 0;
  end
  else if (data_in[0] == 0) begin
    code_out <= 3‘b111;
    en_out <= 1;
    state <= 0;
  end
  else if (data_in == 8‘b11111111) begin
    code_out <= 3‘b111;
    en_out <= 0;
    state <= 1;
  end
  else begin // in case of genetaring latch, while many examples ignore this step
    code_out <= 3‘b111;
    en_out <= 1;
    state <= 1;
  end
end
endmodule

`timescale 1ns/1ps
module coder_83_tb();
  reg [7:0] data_in;
  reg en_in_n, clk;
  wire en_out;
  wire state;
  wire [2:0] code_out;
  
coder_83 u_coder_83(
                    .data_in(data_in),
                    .en_in_n(en_in_n),
                    .en_out(en_out),
                    .state(state),
                    .code_out(code_out)
);

always #20 clk = ~clk;

always@(posedge clk) begin
  if(!data_in)
    data_in <= 8‘b11111111;
  else
    data_in <= data_in << 1;
end

initial begin
  clk = 0;
  data_in = 8‘b11111111;
  en_in_n = 1;
  
# 100 en_in_n = 0;
# 5000 en_in_n = 1;
end
endmodule