A New Implementation of EDSAC

Hatim Kanchwala

Module hierarchy

Generic module structure

Delay line implementation (1)

module delay_line
  #(parameter STORE_LEN  = 16,
    parameter WORD_WIDTH = 36)
   (output reg [STORE_LEN*WORD_WIDTH-1:0] monitor,
    output reg                            data_out,
    input wire                            clk,
    input wire                            data_in,
    input wire                            data_in_gate,
    input wire                            data_clr // Active low. );

   reg [STORE_LEN*WORD_WIDTH-1:0] store;
   integer                        i;

   initial begin
      // Assuming stores in delay lines were cleared.
      monitor = 0;
      store = 0;
      data_out = 1'b0;
   end

Delay line implementation (2)

   // Recirculation logic.
   always @(posedge clk) begin
      for (i = 0; i < STORE_LEN*WORD_WIDTH-1; i = i + 1)
        store[i] <= store[i+1];

      store[STORE_LEN*WORD_WIDTH-1] <= (data_in_gate) ? data_in : (store[0] & data_clr);
   end

   always @(negedge clk) begin
      monitor[STORE_LEN*WORD_WIDTH-1:0] <= store[STORE_LEN*WORD_WIDTH-1:0];
      data_out <= store[0];
   end

endmodule

Use of delay lines in memory

module memory
   (output wire [575:0] monitor, // External long tank display for full 576 bits.
    output wire         mob_tn,
    input wire          clk,
    input wire          mib,
    input wire          tn_in,
    input wire          tn_clr,
    input wire          tn_out );

   delay_line #(.STORE_LEN(16), .WORD_WIDTH(36)) dl
     (.monitor      (monitor),
      .clk          (clk),
      .data_in      (mib),
      .data_in_gate (tn_in),
      .data_clr     (tn_clr) );

   assign mob_tn = tn_out ? monitor[0] : 1'bz;
 endmodule

Control section modules

Computer modules