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`timescale 1ns/100ps

module axi_dacfifo_rd (

 // xfer last for read/write synchronization

  axi_xfer_req,
  axi_rd_lastaddr,

  // axi read address and read data channels

  axi_clk,
  axi_resetn,
  axi_arvalid,
  axi_arid,
  axi_arburst,
  axi_arlock,
  axi_arcache,
  axi_arprot,
  axi_arqos,
  axi_aruser,
  axi_arlen,
  axi_arsize,
  axi_araddr,
  axi_arready,
  axi_rvalid,
  axi_rid,
  axi_ruser,
  axi_rresp,
  axi_rlast,
  axi_rdata,
  axi_rready,

  // axi status

  axi_rerror,

  // fifo interface

  axi_dvalid,
  axi_ddata,
  axi_dready);

  // parameters

  parameter   AXI_DATA_WIDTH = 512;
  parameter   AXI_SIZE = 2;
  parameter   AXI_LENGTH = 15;
  parameter   AXI_ADDRESS = 32'h00000000;
  localparam  AXI_BYTE_WIDTH = AXI_DATA_WIDTH/8;
  localparam  AXI_AWINCR = (AXI_LENGTH + 1) * AXI_BYTE_WIDTH;

  // xfer last for read/write synchronization

  input                           axi_xfer_req;
  input   [ 31:0]                 axi_rd_lastaddr;

  // axi interface

  input                           axi_clk;
  input                           axi_resetn;
  output                          axi_arvalid;
  output  [  3:0]                 axi_arid;
  output  [  1:0]                 axi_arburst;
  output                          axi_arlock;
  output  [  3:0]                 axi_arcache;
  output  [  2:0]                 axi_arprot;
  output  [  3:0]                 axi_arqos;
  output  [  3:0]                 axi_aruser;
  output  [  7:0]                 axi_arlen;
  output  [  2:0]                 axi_arsize;
  output  [ 31:0]                 axi_araddr;
  input                           axi_arready;
  input                           axi_rvalid;
  input   [  3:0]                 axi_rid;
  input   [  3:0]                 axi_ruser;
  input   [  1:0]                 axi_rresp;
  input                           axi_rlast;
  input   [(AXI_DATA_WIDTH-1):0]  axi_rdata;
  output                          axi_rready;

  // axi status

  output                          axi_rerror;

  // fifo interface

  output                          axi_dvalid;
  output  [(AXI_DATA_WIDTH-1):0]  axi_ddata;
  input                           axi_dready;

  // internal registers

  reg     [ 31:0]                 axi_rd_addr_h = 32'b0;
  reg                             axi_rd = 1'b0;
  reg                             axi_rd_active = 1'b0;
  reg                             axi_arvalid = 1'b0;
  reg     [ 31:0]                 axi_araddr = 32'b0;
  reg     [(AXI_DATA_WIDTH-1):0]  axi_ddata = 'b0;
  reg                             axi_dvalid = 1'b0;
  reg                             axi_rready = 1'b0;
  reg                             axi_rerror = 1'b0;
  reg     [ 1:0]                  axi_xfer_req_m = 2'b0;

  // internal signals

  wire                            axi_ready_s;
  wire                            axi_xfer_req_init;
  wire                            axi_dvalid_s;

  assign axi_ready_s = (~axi_arvalid | axi_arready) & axi_dready;

  always @(posedge axi_clk) begin
    if (axi_resetn == 1'b0) begin
      axi_rd <= 1'b0;
      axi_rd_active <= 1'b0;
      axi_xfer_req_m <= 2'b0;
    end else begin
      if (axi_rd_active == 1'b1) begin
        axi_rd <= 1'b0;
        if ((axi_rvalid == 1'b1) && (axi_rlast == 1'b1)) begin
          axi_rd_active <= 1'b0;
        end
      end else if ((axi_ready_s == 1'b1)) begin
        axi_rd <= axi_xfer_req;
        axi_rd_active <= axi_xfer_req;
      end
    axi_xfer_req_m <= {axi_xfer_req_m[0], axi_xfer_req};
    end
  end

  assign axi_xfer_req_init = axi_xfer_req_m[0] & ~axi_xfer_req_m[1];

  // address channel

  assign axi_arid = 4'b0000;
  assign axi_arburst = 2'b01;
  assign axi_arlock = 1'b0;
  assign axi_arcache = 4'b0010;
  assign axi_arprot = 3'b000;
  assign axi_arqos = 4'b0000;
  assign axi_aruser = 4'b0001;
  assign axi_arlen = AXI_LENGTH;
  assign axi_arsize = AXI_SIZE;

  always @(posedge axi_clk) begin
    if (axi_resetn == 1'b0) begin
      axi_arvalid <= 'd0;
      axi_araddr <= 'd0;
      axi_rd_addr_h <= 'd0;
    end else begin
      if (axi_arvalid == 1'b1) begin
        if (axi_arready == 1'b1) begin
          axi_arvalid <= 1'b0;
        end
      end else begin
        if (axi_rd == 1'b1) begin
          axi_arvalid <= 1'b1;
        end
      end
      if ((axi_xfer_req_init == 1'b1)) begin
        axi_araddr <= AXI_ADDRESS;
        axi_rd_addr_h <= axi_rd_lastaddr;
      end else if ((axi_xfer_req == 1'b1) &&
                   (axi_arvalid == 1'b1) &&
                   (axi_arready == 1'b1)) begin
        axi_araddr <= (axi_araddr >= axi_rd_addr_h) ? AXI_ADDRESS : axi_araddr + AXI_AWINCR;
      end
    end
  end

  // read data channel

  assign axi_dvalid_s = axi_rvalid & axi_rready;

  always @(posedge axi_clk) begin
    if (axi_resetn == 1'b0) begin
      axi_ddata <= 'd0;
      axi_rready <= 1'b0;
      axi_dvalid <= 1'b0;
    end else begin
      axi_ddata <= axi_rdata;
      axi_dvalid <= axi_dvalid_s;
      if (axi_xfer_req == 1) begin
        axi_rready <= axi_rvalid;
      end
    end
  end

  always @(posedge axi_clk) begin
    if (axi_resetn == 1'b0) begin
      axi_rerror <= 'd0;
    end else begin
      axi_rerror <= axi_rvalid & axi_rresp[1];
    end
  end

endmodule

// ***************************************************************************
// ***************************************************************************