9086/cpu/processor.v

`timescale 1ns/1ps

module clock_gen (input enable, output reg clk);
  
  parameter FREQ = 1000;  // in HZ
  parameter PHASE = 0;    // in degrees
  parameter DUTY = 50;    // in percentage 
  
  real clk_pd  		= 1.0/FREQ * 1000000; 	// convert to ms
  real clk_on  		= DUTY/100.0 * clk_pd;
  real clk_off 		= (100.0 - DUTY)/100.0 * clk_pd;
  real quarter 		= clk_pd/4;
  real start_dly        = quarter * PHASE/90;
  
  reg start_clk;
  
  initial begin
  end
  
  // Initialize variables to zero
  initial begin
    clk <= 0;
    start_clk <= 0;
  end
  
  // When clock is enabled, delay driving the clock to one in order
  // to achieve the phase effect. start_dly is configured to the 
  // correct delay for the configured phase. When enable is 0,
  // allow enough time to complete the current clock period
  always @ (posedge enable or negedge enable) begin
    if (enable) begin
      #(start_dly) start_clk = 1;
    end else begin
      #(start_dly) start_clk = 0;
    end      
  end
  
  // Achieve duty cycle by a skewed clock on/off time and let this
  // run as long as the clocks are turned on.
  always @(posedge start_clk) begin
    if (start_clk) begin
      	clk = 1;
      
      	while (start_clk) begin
      		#(clk_on)  clk = 0;
    		#(clk_off) clk = 1;
        end
      
      	clk = 0;
    end
  end 
endmodule


module processor ( input clock, input reset , output reg [19:0] external_address_bus, inout [15:0] external_data_bus,output reg read, output reg write);
  /* State */
  reg [1:0] state;
  reg start=0;
  reg instruction_finished;

  /* Registers */
  reg [19:0] ProgCount;


  /* RESET LOGIC */
  always @(negedge reset) begin
    if (reset==0) begin
      @(posedge clock);
      state=0;
      ProgCount=0;//TODO: Reset Vector
      #10
      start=1;
    end
  end

  /* CLOCK LOGIC */
  always @(posedge clock) begin
    if(instruction_finished) begin 
      state =0;
    end else begin
      if (clock && start==1) begin
        state=state+1;
      end
    end
  end

  always @(state) begin
	  if (state==2) begin
		  instruction_finished=1;
	  end else begin
		  instruction_finished=0;
	  end
  end

  /* Processor stages */
  always @(state) begin
	  if (state==0) begin
		external_address_bus <= ProgCount;
		read <= 0;
		write <= 1;
	end
  end

endmodule