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

`timescale 1ns/100ps

module axi_dacfifo_dac (

  axi_clk,
  axi_dvalid,
  axi_ddata,
  axi_dready,
  axi_xfer_req,

  dma_last_addr,

  dac_clk,
  dac_rst,
  dac_valid,
  dac_data,
  dac_xfer_out,
  dac_dunf
);

  // parameters

  parameter   AXI_DATA_WIDTH = 512;
  parameter   AXI_LENGTH = 15;
  parameter   DAC_DATA_WIDTH = 64;

  localparam  MEM_RATIO = AXI_DATA_WIDTH/DAC_DATA_WIDTH;
  localparam  DAC_ADDRESS_WIDTH = 10;
  localparam  AXI_ADDRESS_WIDTH = (MEM_RATIO == 1) ? DAC_ADDRESS_WIDTH :
                                  (MEM_RATIO == 2) ? (DAC_ADDRESS_WIDTH - 1) :
                                  (MEM_RATIO == 4) ? (DAC_ADDRESS_WIDTH - 2) :
                                                     (DAC_ADDRESS_WIDTH - 3);

  // BUF_THRESHOLD_LO will make sure that there are always at least two burst in the memmory
  localparam  AXI_BUF_THRESHOLD_LO = 3 * (AXI_LENGTH+1);
  localparam  AXI_BUF_THRESHOLD_HI = {(AXI_ADDRESS_WIDTH){1'b1}} - (AXI_LENGTH+1);
  localparam  DAC_BUF_THRESHOLD_LO = 3 * (AXI_LENGTH+1) * MEM_RATIO;
  localparam  DAC_BUF_THRESHOLD_HI = {(DAC_ADDRESS_WIDTH){1'b1}} - (AXI_LENGTH+1) * MEM_RATIO;
  localparam  DAC_ARINCR = (AXI_LENGTH+1) * MEM_RATIO;

  // dma write

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

  input   [31:0]                      dma_last_addr;

  // dac read

  input                               dac_clk;
  input                               dac_rst;
  input                               dac_valid;
  output  [(DAC_DATA_WIDTH-1):0]      dac_data;
  output                              dac_xfer_out;
  output                              dac_dunf;

  // internal registers

  reg     [(AXI_ADDRESS_WIDTH-1):0]   axi_mem_waddr = 'd0;
  reg     [(DAC_ADDRESS_WIDTH-1):0]   axi_mem_waddr_g = 'd0;
  reg     [(DAC_ADDRESS_WIDTH-1):0]   axi_mem_raddr = 'd0;
  reg     [(DAC_ADDRESS_WIDTH-1):0]   axi_mem_raddr_m1 = 'd0;
  reg     [(DAC_ADDRESS_WIDTH-1):0]   axi_mem_raddr_m2 = 'd0;
  reg     [(AXI_ADDRESS_WIDTH-1):0]   axi_mem_addr_diff = 'd0;
  reg                                 axi_dready = 'd0;

  reg     [(DAC_ADDRESS_WIDTH-1):0]   dac_mem_raddr = 'd0;
  reg     [(DAC_ADDRESS_WIDTH-1):0]   dac_mem_raddr_next = 'd0;
  reg     [(DAC_ADDRESS_WIDTH-1):0]   dac_mem_raddr_g = 'd0;
  reg     [(DAC_ADDRESS_WIDTH-1):0]   dac_mem_waddr = 'd0;
  reg     [(DAC_ADDRESS_WIDTH-1):0]   dac_mem_waddr_m1 = 'd0;
  reg     [(DAC_ADDRESS_WIDTH-1):0]   dac_mem_waddr_m2 = 'd0;
  reg     [(DAC_ADDRESS_WIDTH-1):0]   dac_mem_addr_diff = 'd0;
  reg                                 dac_mem_init = 1'b0;
  reg                                 dac_mem_init_d = 1'b0;
  reg                                 dac_mem_enable = 1'b0;

  reg     [ 2:0]                      dac_xfer_req_m = 3'b0;
  reg                                 dac_xfer_init = 1'b0;

  reg     [31:0]                      dac_raddr_cnt = 32'b0;
  reg     [31:0]                      dac_last_raddr = 32'b0;
  reg     [31:0]                      dac_last_raddr_m = 32'b0;
  reg                                 dac_almost_full = 1'b0;
  reg                                 dac_almost_empty = 1'b0;
  reg                                 dac_dunf = 1'b0;

  // internal signals

  wire    [AXI_ADDRESS_WIDTH:0]       axi_mem_addr_diff_s;
  wire    [(AXI_ADDRESS_WIDTH-1):0]   axi_mem_raddr_s;
  wire    [(DAC_ADDRESS_WIDTH-1):0]   axi_mem_waddr_s;

  wire    [DAC_ADDRESS_WIDTH:0]       dac_mem_addr_diff_s;
  wire    [DAC_ADDRESS_WIDTH:0]       dac_mem_raddr_diff_s;
  wire    [(DAC_ADDRESS_WIDTH-1):0]   dac_mem_waddr_s;
  wire                                dac_mem_valid_s;
  wire                                dac_xfer_init_s;

  // binary to grey conversion

  function [9:0] b2g;
    input [9:0] b;
    reg   [9:0] g;
    begin
      g[9] = b[9];
      g[8] = b[9] ^ b[8];
      g[7] = b[8] ^ b[7];
      g[6] = b[7] ^ b[6];
      g[5] = b[6] ^ b[5];
      g[4] = b[5] ^ b[4];
      g[3] = b[4] ^ b[3];
      g[2] = b[3] ^ b[2];
      g[1] = b[2] ^ b[1];
      g[0] = b[1] ^ b[0];
      b2g = g;
    end
  endfunction

  // grey to binary conversion

  function [9:0] g2b;
    input [9:0] g;
    reg   [9:0] b;
    begin
      b[9] = g[9];
      b[8] = b[9] ^ g[8];
      b[7] = b[8] ^ g[7];
      b[6] = b[7] ^ g[6];
      b[5] = b[6] ^ g[5];
      b[4] = b[5] ^ g[4];
      b[3] = b[4] ^ g[3];
      b[2] = b[3] ^ g[2];
      b[1] = b[2] ^ g[1];
      b[0] = b[1] ^ g[0];
      g2b = b;
    end
  endfunction

  // write interface

  always @(posedge axi_clk) begin
    if (axi_xfer_req == 1'b0) begin
      axi_mem_waddr <= 'd0;
      axi_mem_waddr_g <= 'd0;
    end else begin
      if (axi_dvalid == 1'b1) begin
        axi_mem_waddr <= axi_mem_waddr + 1'b1;
      end
      axi_mem_waddr_g <= b2g(axi_mem_waddr_s);
    end
  end

  // scale the axi_mem_* addresses

  assign axi_mem_raddr_s = (MEM_RATIO == 1) ? axi_mem_raddr :
                           (MEM_RATIO == 2) ? axi_mem_raddr[(DAC_ADDRESS_WIDTH-1):1] :
                           (MEM_RATIO == 4) ? axi_mem_raddr[(DAC_ADDRESS_WIDTH-1):2] :
                                              axi_mem_raddr[(DAC_ADDRESS_WIDTH-1):3];
  assign axi_mem_waddr_s = (MEM_RATIO == 1) ? axi_mem_waddr :
                           (MEM_RATIO == 2) ? {axi_mem_waddr, 1'b0} :
                           (MEM_RATIO == 4) ? {axi_mem_waddr, 2'b0} :
                                              {axi_mem_waddr, 3'b0};

  // incomming data flow control

  assign axi_mem_addr_diff_s = {1'b1, axi_mem_waddr} - axi_mem_raddr_s;

  always @(posedge axi_clk) begin
    if (axi_xfer_req == 1'b0) begin
      axi_mem_addr_diff <= 'd0;
      axi_mem_raddr <= 'd0;
      axi_mem_raddr_m1 <= 'd0;
      axi_mem_raddr_m2 <= 'd0;
      axi_dready <= 'd0;
    end else begin
      axi_mem_raddr_m1 <= dac_mem_raddr_g;
      axi_mem_raddr_m2 <= axi_mem_raddr_m1;
      axi_mem_raddr <= g2b(axi_mem_raddr_m2);
      axi_mem_addr_diff <= axi_mem_addr_diff_s[AXI_ADDRESS_WIDTH-1:0];
      if (axi_mem_addr_diff >= AXI_BUF_THRESHOLD_HI) begin
        axi_dready <= 1'b0;
      end else if (axi_mem_addr_diff <= AXI_BUF_THRESHOLD_LO) begin
        axi_dready <= 1'b1;
      end
    end
  end

  // CDC for xfer_req signal

  always @(posedge dac_clk) begin
    if (dac_rst == 1'b1) begin
      dac_xfer_req_m <= 3'b0;
    end else begin
      dac_xfer_req_m <= {dac_xfer_req_m[1:0], axi_xfer_req};
    end
  end

  assign dac_xfer_out = dac_xfer_req_m[2];
  assign dac_xfer_init_s = ~dac_xfer_req_m[2] & dac_xfer_req_m[1];

  // read interface

  always @(posedge dac_clk) begin
    if (dac_xfer_out == 1'b0) begin
      dac_mem_init <= 1'b0;
      dac_mem_init_d <= 1'b0;
      dac_mem_enable <= 1'b0;
    end else begin
      if (dac_xfer_init == 1'b1) begin
        dac_mem_init <= 1'b1;
      end
      if ((dac_mem_init == 1'b1) && (dac_mem_addr_diff > DAC_BUF_THRESHOLD_LO)) begin
        dac_mem_init <= 1'b0;
      end
      dac_mem_init_d <= dac_mem_init;
      // memory is ready when the initial fill up is done
      dac_mem_enable <= (dac_mem_init_d & ~dac_mem_init) ? 1'b1 : dac_mem_enable;
    end
    dac_xfer_init <= dac_xfer_init_s;
  end

  always @(posedge dac_clk) begin
    if (dac_xfer_out == 1'b0) begin
      dac_mem_waddr <= 'b0;
      dac_mem_waddr_m1 <= 'b0;
      dac_mem_waddr_m2 <= 'b0;
    end else begin
      dac_mem_waddr_m1 <= axi_mem_waddr_g;
      dac_mem_waddr_m2 <= dac_mem_waddr_m1;
      dac_mem_waddr <= g2b(dac_mem_waddr_m2);
    end
  end

  assign dac_mem_addr_diff_s = {1'b1, dac_mem_waddr} - dac_mem_raddr;
  assign dac_mem_raddr_diff_s = {1'b1, dac_mem_raddr_next} - dac_mem_raddr;
  assign dac_mem_valid_s = (dac_mem_enable) ? dac_valid : 1'b0;

  // CDC for the dma_last_addr

  always @(posedge dac_clk) begin
    if (dac_rst == 1'b1) begin
      dac_last_raddr <= 32'b0;
      dac_last_raddr_m <= 32'b0;
    end else begin
      dac_last_raddr_m <= dma_last_addr;
      dac_last_raddr <= dac_last_raddr_m;
    end
  end

  always @(posedge dac_clk) begin
    if (dac_xfer_out == 1'b0) begin
      dac_mem_raddr <= 'd0;
      dac_mem_raddr_next <= DAC_ARINCR;
      dac_mem_raddr_g <= 'd0;
      dac_mem_addr_diff <= 'd0;
    end else begin
      dac_mem_addr_diff <= dac_mem_addr_diff_s[DAC_ADDRESS_WIDTH-1:0];
      if (dac_mem_valid_s == 1'b1) begin
        dac_raddr_cnt <= (dac_raddr_cnt == dac_last_raddr) ? 32'b0 : dac_raddr_cnt + 1;
        dac_mem_raddr <= (dac_raddr_cnt == dac_last_raddr) ? dac_mem_raddr_next : dac_mem_raddr + 1'b1;
      end
      dac_mem_raddr_next <= (dac_mem_raddr_diff_s[DAC_ADDRESS_WIDTH-1:0] <= 1) ? dac_mem_raddr_next + DAC_ARINCR : dac_mem_raddr_next;
      dac_mem_raddr_g <= b2g(dac_mem_raddr);
    end
  end

  // underflow generation, there is no overflow

  always @(posedge dac_clk) begin
    if(dac_xfer_out == 1'b0) begin
      dac_almost_full <= 1'b0;
      dac_almost_empty <= 1'b0;
      dac_dunf <= 1'b0;
    end else begin
      if (dac_mem_addr_diff < DAC_BUF_THRESHOLD_LO) begin
        dac_almost_empty <= 1'b1;
      end else begin
        dac_almost_empty <= 1'b0;
      end
      dac_dunf <= (dac_mem_addr_diff == 1'b0) ? 1'b1 : 1'b0;
    end
  end

  // instantiations

  ad_mem_asym #(
    .A_ADDRESS_WIDTH (AXI_ADDRESS_WIDTH),
    .A_DATA_WIDTH (AXI_DATA_WIDTH),
    .B_ADDRESS_WIDTH (DAC_ADDRESS_WIDTH),
    .B_DATA_WIDTH (DAC_DATA_WIDTH))
  i_mem_asym (
    .clka (axi_clk),
    .wea (axi_dvalid),
    .addra (axi_mem_waddr),
    .dina (axi_ddata),
    .clkb (dac_clk),
    .addrb (dac_mem_raddr),
    .doutb (dac_data));

endmodule

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