Subversion Repositories eco32

module ata_io (clk, reset,

               bus_en, bus_wr, bus_addr, bus_din, bus_dout, bus_wait,

               ata_d, ata_a, ata_cs0_n, ata_cs1_n,

               ata_dior_n, ata_diow_n, ata_iordy);

    input clk;

    input reset;

    //

    input bus_en;

    input bus_wr;

    input [3:0] bus_addr;

    input [15:0] bus_din;

    output reg [15:0] bus_dout;

    output bus_wait;

    //

    inout [15:0] ata_d;

    output reg [2:0] ata_a;

    output reg ata_cs0_n;

    output reg ata_cs1_n;

    output reg ata_dior_n;

    output reg ata_diow_n;

    input ata_iordy;

  reg [2:0] state;

  reg [4:0] delay_counter;

  reg ata_d_drive;

  assign ata_d = ata_d_drive ? bus_din : 16'bzzzzzzzzzzzzzzzz;

  assign bus_wait = bus_en & (state != 3'd5);

  always @(posedge clk) begin

    if (reset == 1'b1) begin

      state <= 3'd0;

      delay_counter <= 5'd31;

      ata_d_drive <= 1'b0;

      ata_a <= 3'b000;

      ata_cs0_n <= 1'b1;

      ata_cs1_n <= 1'b1;

      ata_dior_n <= 1'b1;

      ata_diow_n <= 1'b1;

      bus_dout <= 16'd0;

    end else begin

      if (delay_counter == 5'd0) begin

        case (state)

          // ready - wait for request from the bus

          3'd0: begin

            if (bus_en & ata_iordy) begin

              // assert address and -> state 1, wait 3+1

              // address mapping

              //   0xxx : control block registers

              //   1xxx : command block registers

              ata_a[2:0] <= bus_addr[2:0];

              ata_cs0_n <= ~bus_addr[3];

              ata_cs1_n <= bus_addr[3];

              state <= 3'd1;

              delay_counter <= 5'd3;

            end

          end

          // assert data-out and RW strobes, then -> state 2, wait 14+1

          3'd1: begin

            ata_d_drive <= bus_wr;

            ata_dior_n <= bus_wr;

            ata_diow_n <= ~bus_wr;

            state <= 3'd2;

            delay_counter <= 5'd14;

          end

          // de-assert RW strobes and sample data-in,

          // then -> state 3, wait 1+1

          3'd2: begin

            bus_dout <= ata_d;

            ata_dior_n <= 1'b1;

            ata_diow_n <= 1'b1;

            state <= 3'd3;

            delay_counter <= 5'd1;

          end

          // de-assert data and address, then -> state 4, wait 7+1

          // (such that 600 ns min cycle time is satisfied)

          3'd3: begin

            ata_d_drive <= 1'b0;

            ata_cs0_n <= 1'b1;

            ata_cs1_n <= 1'b1;

            state <= 3'd4;

            delay_counter <= 5'd7;

          end

          // auxiliary state, for necessity see comment in state 5

          3'd4: begin

            state <= 3'd5;

            delay_counter <= 5'd0;

          end

          // finish - used to release bus wait

          // WARNING: This state must not be entered with a delay!

          // Otherwise bus wait will be released too early and

          // subsequent bus cycles will not work properly.

          3'd5: begin

            state <= 3'd0;

            delay_counter <= 5'd0;

          end

        endcase

      end else begin

        delay_counter <= delay_counter - 1;

      end

    end

  end

endmodule