// SPDX-License-Identifier: LGPL-3.0-or-later
//
// Vivado/XPM replacement for the legacy Ettus FIFO Generator building blocks
// used by axi_fifo_2clk.v on Xilinx 7-series devices.
//
// This core deliberately provides the old native FIFO interface while using
// xpm_fifo_async internally.  The external reset may be asynchronous, as it
// was for the FIFO Generator instances.  XPM's rst input, however, must be
// synchronous to wr_clk, so reset assertion is captured asynchronously and
// then presented to XPM through a wr_clk synchronizer.  Read/write requests
// and external flags are held inactive/conservative until XPM reset-busy has
// cleared.

`timescale 1ns/1ps
`default_nettype none

module fifo_2clk_xpm_core #(
  parameter integer FIFO_DEPTH      = 32,
  parameter integer COUNT_WIDTH     = 6,
  parameter integer CDC_SYNC_STAGES = 3,
  parameter         MEMORY_TYPE     = "distributed"
)(
  input  wire                    rst,
  input  wire                    wr_clk,
  input  wire [71:0]             din,
  input  wire                    wr_en,
  output wire                    full,
  output wire [COUNT_WIDTH-1:0]  wr_data_count,
  input  wire                    rd_clk,
  output wire [71:0]             dout,
  input  wire                    rd_en,
  output wire                    empty,
  output wire [COUNT_WIDTH-1:0]  rd_data_count
);

  // ------------------------------------------------------------------------
  // Reset adaptation
  // ------------------------------------------------------------------------
  // Legacy FIFO Generator accepted an asynchronous reset. XPM_FIFO_ASYNC
  // requires rst to be synchronous to wr_clk. rst_capture catches even a
  // short asynchronous assertion; xpm_rst_sync then converts it into a reset
  // signal that changes only on wr_clk edges.
  reg rst_capture = 1'b1;
  always @(posedge wr_clk or posedge rst) begin
    if (rst)
      rst_capture <= 1'b1;
    else
      rst_capture <= 1'b0;
  end

  (* ASYNC_REG = "TRUE", SHREG_EXTRACT = "NO" *)
  reg [1:0] xpm_rst_sync = 2'b11;
  always @(posedge wr_clk) begin
    xpm_rst_sync[0] <= rst_capture;
    xpm_rst_sync[1] <= xpm_rst_sync[0];
  end

  wire xpm_rst = xpm_rst_sync[1];

  wire xpm_full;
  wire xpm_empty;
  wire xpm_wr_rst_busy;
  wire xpm_rd_rst_busy;
  wire [71:0] xpm_dout;
  wire [COUNT_WIDTH-1:0] xpm_wr_data_count;
  wire [COUNT_WIDTH-1:0] xpm_rd_data_count;

  // Keep the read-side legacy interface quiescent from the instant the old
  // asynchronous reset is asserted until both XPM reset propagation and the
  // read-domain reset-busy interval have completed. Assertion is asynchronous;
  // release is synchronized to rd_clk.
  wire rd_hold_req = rst | xpm_rst | xpm_rd_rst_busy;
  (* ASYNC_REG = "TRUE", SHREG_EXTRACT = "NO" *)
  reg [1:0] rd_hold_sync = 2'b11;
  always @(posedge rd_clk or posedge rd_hold_req) begin
    if (rd_hold_req)
      rd_hold_sync <= 2'b11;
    else begin
      rd_hold_sync[0] <= 1'b0;
      rd_hold_sync[1] <= rd_hold_sync[0];
    end
  end

  wire rd_hold = rd_hold_sync[1];
  wire wr_hold = rst | xpm_rst | xpm_wr_rst_busy;

  // XPM requires wr_en/rd_en low while reset or the corresponding reset-busy
  // flag is active. Gating with full/empty also suppresses overflow/underflow
  // requests from legacy call sites that leave an enable asserted continuously.
  wire xpm_wr_en = wr_en & ~wr_hold & ~xpm_full;
  wire xpm_rd_en = rd_en & ~rd_hold & ~xpm_empty;

  // Match the conservative reset behavior of the Ettus FIFO Generator IP:
  // full is asserted during reset and empty is asserted until read-side reset
  // recovery is complete.
  assign full          = wr_hold | xpm_full;
  assign empty         = rd_hold | xpm_empty;
  assign dout          = rd_hold ? 72'b0 : xpm_dout;
  assign wr_data_count = wr_hold ? {COUNT_WIDTH{1'b0}} : xpm_wr_data_count;
  assign rd_data_count = rd_hold ? {COUNT_WIDTH{1'b0}} : xpm_rd_data_count;

  // USE_ADV_FEATURES="0404" enables only wr_data_count (bit 2) and
  // rd_data_count (bit 10), preserving the legacy ports without enabling the
  // other optional status logic.
  xpm_fifo_async #(
    .CDC_SYNC_STAGES    (CDC_SYNC_STAGES),
    .DOUT_RESET_VALUE   ("0"),
    .ECC_MODE           ("no_ecc"),
    .FIFO_MEMORY_TYPE   (MEMORY_TYPE),
    .FIFO_READ_LATENCY  (0),
    .FIFO_WRITE_DEPTH   (FIFO_DEPTH),
    .FULL_RESET_VALUE   (1),
    .PROG_EMPTY_THRESH  (10),
    .PROG_FULL_THRESH   (10),
    .RD_DATA_COUNT_WIDTH(COUNT_WIDTH),
    .READ_DATA_WIDTH    (72),
    .READ_MODE          ("fwft"),
    .RELATED_CLOCKS     (0),
    .SIM_ASSERT_CHK     (1),
    .USE_ADV_FEATURES   ("0404"),
    .WAKEUP_TIME        (0),
    .WRITE_DATA_WIDTH   (72),
    .WR_DATA_COUNT_WIDTH(COUNT_WIDTH)
  ) xpm_fifo_async_i (
    .almost_empty (),
    .almost_full  (),
    .data_valid   (),
    .dbiterr      (),
    .dout         (xpm_dout),
    .empty        (xpm_empty),
    .full         (xpm_full),
    .overflow     (),
    .prog_empty   (),
    .prog_full    (),
    .rd_data_count(xpm_rd_data_count),
    .rd_rst_busy  (xpm_rd_rst_busy),
    .sbiterr      (),
    .underflow    (),
    .wr_ack       (),
    .wr_data_count(xpm_wr_data_count),
    .wr_rst_busy  (xpm_wr_rst_busy),
    .din          (din),
    .injectdbiterr(1'b0),
    .injectsbiterr(1'b0),
    .rd_clk       (rd_clk),
    .rd_en        (xpm_rd_en),
    .rst          (xpm_rst),
    .sleep        (1'b0),
    .wr_clk       (wr_clk),
    .wr_en        (xpm_wr_en)
  );

endmodule

`default_nettype wire