clk_gen.v

来自「A Relatively Simple RISC CPU 设计源码并附详细的说明」· Verilog 代码 · 共 85 行

module clk_gen (clk,reset,clk1,clk2,clk4,fetch,alu_clk);
input clk,reset;
output clk1,clk2,clk4,fetch,alu_clk;
wire clk,reset;
reg clk2,clk4,fetch,alu_clk;
reg[7:0] state;
parameter    S1 = 8'b00000001,
             S2 = 8'b00000010,
             S3 = 8'b00000100,
             S4 = 8'b00001000,
             S5 = 8'b00010000,
             S6 = 8'b00100000,
             S7 = 8'b01000000,
             S8 = 8'b10000000,
           idle = 8'b00000000;
                 
assign clk1 = ~clk;

always @(negedge clk)
   if(reset)
           begin
                clk2 <= 0;
                clk4 <= 1;
                fetch  <= 0;
                alu_clk <= 0;
                state <= idle;
           end
   else
           begin 
              case(state)
                 S1:
                      begin
                            clk2 <= ~clk2;
                         alu_clk <= ~alu_clk;                
                           state <= S2;
                      end
                 S2:
                      begin
                          clk2 <= ~clk2;
                          clk4 <= ~clk4;
                       alu_clk <= ~alu_clk;
                         state <= S3;
                      end
                 S3:
                      begin   
                          clk2 <= ~clk2;
                         state <= S4;
                      end
                 S4:
                      begin
                          clk2  <= ~clk2;
                          clk4  <= ~clk4;
                          fetch <= ~fetch;
                          state <= S5;
                      end
                 S5:
                       begin
                          clk2  <= ~clk2;
                          state <= S6;
                       end
                 S6:
                       begin
                           clk2  <= ~clk2;
                            clk4 <= ~clk4;
                           state <= S7;
                        end
                 S7:
                        begin
                             clk2  <= ~clk2;
                             state <=  S8;
                        end
                 S8:
                        begin
                             clk2 <= ~clk2;
                            clk4  <= ~clk4;
                            fetch <= ~fetch;
                            state <= S1;
                        end
                idle:       state <= S1;   
                default:    state <= idle;               
            endcase
     end
endmodule