// ***************************************************************************
// ***************************************************************************
// Copyright 2014 - 2017 (c) Analog Devices, Inc. All rights reserved.
//
// In this HDL repository, there are many different and unique modules, consisting
// of various HDL (Verilog or VHDL) components. The individual modules are
// developed independently, and may be accompanied by separate and unique license
// terms.
//
// The user should read each of these license terms, and understand the
// freedoms and responsibilities that he or she has by using this source/core.
//
// This core is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
// A PARTICULAR PURPOSE.
//
// Redistribution and use of source or resulting binaries, with or without modification
// of this file, are permitted under one of the following two license terms:
//
//   1. The GNU General Public License version 2 as published by the
//      Free Software Foundation, which can be found in the top level directory
//      of this repository (LICENSE_GPL2), and also online at:
//      <https://www.gnu.org/licenses/old-licenses/gpl-2.0.html>
//
// OR
//
//   2. An ADI specific BSD license, which can be found in the top level directory
//      of this repository (LICENSE_ADIBSD), and also on-line at:
//      https://github.com/analogdevicesinc/hdl/blob/master/LICENSE_ADIBSD
//      This will allow to generate bit files and not release the source code,
//      as long as it attaches to an ADI device.
//
// ***************************************************************************
// ***************************************************************************

`timescale 1ns/100ps

module axi_dmac_response_manager #(
  parameter DMA_DATA_WIDTH_SRC = 64,
  parameter DMA_DATA_WIDTH_DEST = 64,
  parameter DMA_LENGTH_WIDTH = 24,
  parameter BYTES_PER_BURST_WIDTH = 7,
  parameter BYTES_PER_BEAT_WIDTH_SRC = $clog2(DMA_DATA_WIDTH_SRC/8),
  parameter ASYNC_CLK_DEST_REQ = 1
) (

  // Interface to destination side
  input dest_clk,
  input dest_resetn,

  input dest_response_valid,
  output dest_response_ready,
  input [1:0] dest_response_resp,
  input dest_response_partial,
  input dest_response_resp_eot,
  input [BYTES_PER_BURST_WIDTH-1:0] dest_response_data_burst_length,

  // Interface to processor
  input req_clk,
  input req_resetn,

  output response_eot,
  output reg [BYTES_PER_BURST_WIDTH-1:0] measured_burst_length = 'h0,
  output response_partial,
  output reg response_valid = 1'b0,
  input response_ready,

  // Interface to requester side
  input completion_req_valid,
  output reg completion_req_ready = 1'b1,
  input completion_req_last,
  input [1:0] completion_transfer_id
);

  localparam STATE_IDLE         = 3'h0;
  localparam STATE_ACC          = 3'h1;
  localparam STATE_WRITE_RESPR  = 3'h2;
  localparam STATE_ZERO_COMPL   = 3'h3;
  localparam STATE_WRITE_ZRCMPL = 3'h4;

  reg [2:0] state = STATE_IDLE;
  reg [2:0] nx_state;

  localparam DEST_SRC_RATIO = DMA_DATA_WIDTH_DEST/DMA_DATA_WIDTH_SRC;

  localparam DEST_SRC_RATIO_WIDTH = DEST_SRC_RATIO > 64 ? 7 :
    DEST_SRC_RATIO > 32 ? 6 :
    DEST_SRC_RATIO > 16 ? 5 :
    DEST_SRC_RATIO > 8 ? 4 :
    DEST_SRC_RATIO > 4 ? 3 :
    DEST_SRC_RATIO > 2 ? 2 :
    DEST_SRC_RATIO > 1 ? 1 : 0;

  localparam BYTES_PER_BEAT_WIDTH = DEST_SRC_RATIO_WIDTH + BYTES_PER_BEAT_WIDTH_SRC;
  localparam BURST_LEN_WIDTH = BYTES_PER_BURST_WIDTH - BYTES_PER_BEAT_WIDTH;

  wire do_acc_st;
  wire do_compl;
  reg req_eot = 1'b0;
  reg req_response_partial = 1'b0;
  reg [BYTES_PER_BURST_WIDTH-1:0] req_response_dest_data_burst_length = 'h0;

  wire response_dest_valid;
  reg response_dest_ready = 1'b1;
  wire [1:0] response_dest_resp;
  wire response_dest_resp_eot;
  wire [BYTES_PER_BURST_WIDTH-1:0] response_dest_data_burst_length;

  wire completion_req;

  reg [1:0] to_complete_count = 'h0;
  reg [1:0] transfer_id = 'h0;
  reg completion_req_last_found = 1'b0;

  util_axis_fifo #(
    .DATA_WIDTH(BYTES_PER_BURST_WIDTH+1+1),
    .ADDRESS_WIDTH(0),
    .ASYNC_CLK(ASYNC_CLK_DEST_REQ)
  ) i_dest_response_fifo (
    .s_axis_aclk(dest_clk),
    .s_axis_aresetn(dest_resetn),
    .s_axis_valid(dest_response_valid),
    .s_axis_ready(dest_response_ready),
    .s_axis_full(),
    .s_axis_data({dest_response_data_burst_length,
                  dest_response_partial,
                  dest_response_resp_eot}),
    .s_axis_room(),

    .m_axis_aclk(req_clk),
    .m_axis_aresetn(req_resetn),
    .m_axis_valid(response_dest_valid),
    .m_axis_ready(response_dest_ready),
    .m_axis_data({response_dest_data_burst_length,
                  response_dest_partial,
                  response_dest_resp_eot}),
    .m_axis_level(),
    .m_axis_empty());

  always @(posedge req_clk)
  begin
    if (response_dest_valid & response_dest_ready) begin
      req_eot <= response_dest_resp_eot;
      req_response_partial <= response_dest_partial;
      req_response_dest_data_burst_length <= response_dest_data_burst_length;
    end
  end

  always @(posedge req_clk)
  begin
    if (req_resetn == 1'b0) begin
      response_dest_ready <= 1'b1;
    end else begin
      response_dest_ready <= (nx_state == STATE_IDLE);
    end
  end

  assign response_eot = (state == STATE_WRITE_RESPR) ? req_eot : 1'b1;
  assign response_partial = (state == STATE_WRITE_RESPR) ? req_response_partial : 1'b0;

  always @(posedge req_clk)
  begin
    if (req_resetn == 1'b0) begin
      response_valid <= 1'b0;
    end else begin
      if (nx_state == STATE_WRITE_RESPR || nx_state == STATE_WRITE_ZRCMPL) begin
        response_valid <= 1'b1;
      end else if (response_ready == 1'b1) begin
        response_valid <= 1'b0;
      end
    end
  end

  always @(posedge req_clk)
  begin
    if (state == STATE_ZERO_COMPL) begin
      measured_burst_length <= {BYTES_PER_BURST_WIDTH{1'b1}};
    end else if (state == STATE_ACC) begin
      measured_burst_length <= req_response_dest_data_burst_length;
    end
  end

  always @(*) begin
    nx_state = state;
    case (state)
      STATE_IDLE: begin
        if (response_dest_valid == 1'b1) begin
          nx_state = STATE_ACC;
        end else if (|to_complete_count) begin
          if (transfer_id == completion_transfer_id)
            nx_state = STATE_ZERO_COMPL;
        end
      end
      STATE_ACC: begin
        nx_state = STATE_WRITE_RESPR;
      end
      STATE_WRITE_RESPR: begin
        if (response_ready == 1'b1) begin
          if (|to_complete_count && transfer_id == completion_transfer_id) begin
            nx_state = STATE_ZERO_COMPL;
          end else begin
            nx_state = STATE_IDLE;
          end
        end
      end
      STATE_ZERO_COMPL: begin
        if (|to_complete_count) begin
          nx_state = STATE_WRITE_ZRCMPL;
        end else begin
          if (completion_req_last_found == 1'b1) begin
            nx_state = STATE_IDLE;
          end
        end
      end
      STATE_WRITE_ZRCMPL:begin
        if (response_ready == 1'b1) begin
          nx_state = STATE_ZERO_COMPL;
        end
      end
      default: begin
        nx_state = STATE_IDLE;
      end
    endcase
  end

  always @(posedge req_clk) begin
    if (req_resetn == 1'b0) begin
      state <= STATE_IDLE;
    end else begin
      state <= nx_state;
    end
  end

  assign do_compl = (state == STATE_WRITE_ZRCMPL) && response_ready;

  // Once the last completion request from request generator is received
  // we can wait for completions from the destination side
  always @(posedge req_clk) begin
    if (req_resetn == 1'b0) begin
      completion_req_last_found <= 1'b0;
    end else if (completion_req) begin
      completion_req_last_found <= completion_req_last;
    end else if (state ==STATE_ZERO_COMPL && ~(|to_complete_count)) begin
      completion_req_last_found <= 1'b0;
    end
  end

  // Once the last completion is received wit until all completions are done
  always @(posedge req_clk) begin
    if (req_resetn == 1'b0) begin
      completion_req_ready <= 1'b1;
    end else if (completion_req_valid && completion_req_last) begin
      completion_req_ready <= 1'b0;
    end else if (to_complete_count == 0) begin
      completion_req_ready <= 1'b1;
    end
  end

  assign completion_req = completion_req_ready && completion_req_valid;

  // Track transfers so we can tell when did the destination completed all its
  // transfers
  always @(posedge req_clk) begin
    if (req_resetn == 1'b0) begin
      transfer_id <= 'h0;
    end else if ((state == STATE_ACC && req_eot) || do_compl) begin
      transfer_id <= transfer_id + 1;
    end
  end

  // Count how many transfers we need to complete
  always @(posedge req_clk) begin
    if (req_resetn == 1'b0) begin
      to_complete_count <= 'h0;
    end else if (completion_req & ~do_compl) begin
      to_complete_count <= to_complete_count + 1;
    end else if (~completion_req & do_compl) begin
      to_complete_count <= to_complete_count - 1;
    end
  end

endmodule