// ***************************************************************************
// ***************************************************************************
// Copyright (C) 2014-2023 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 request_generator #(

  parameter ID_WIDTH = 3,
  parameter BURSTS_PER_TRANSFER_WIDTH = 17
) (
  input clk,
  input resetn,

  output [ID_WIDTH-1:0] request_id,
  input [ID_WIDTH-1:0] response_id,

  input rewind_req_valid,
  output rewind_req_ready,
  input [ID_WIDTH+3-1:0] rewind_req_data,
  output rewind_state,

  output abort_req,

  output reg completion_req_valid = 1'b0,
  input completion_req_ready,
  output completion_req_last,
  output [1:0] completion_transfer_id,

  input req_valid,
  output reg req_ready,
  input [BURSTS_PER_TRANSFER_WIDTH-1:0] req_burst_count,
  input req_xlast,

  input enable,

  output eot
);

  `include "inc_id.vh"

  localparam STATE_IDLE      = 3'h0;
  localparam STATE_GEN_ID    = 3'h1;
  localparam STATE_REWIND_ID = 3'h2;
  localparam STATE_CONSUME   = 3'h3;
  localparam STATE_WAIT_LAST = 3'h4;

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

  reg [1:0] rew_transfer_id = 1'b0;
  reg rew_req_xlast;
  reg [ID_WIDTH-1:0] rew_id = 'h0;

  reg cur_transfer_id = 1'b0;
  reg cur_req_xlast;

  wire transfer_id_match;
  reg nx_completion_req_valid;

  /*
   * Here we only need to count the number of bursts, which means we can ignore
   * the lower bits of the byte count. The last last burst may not contain the
   * maximum number of bytes, but the address_generator and data_mover will take
   * care that only the requested ammount of bytes is transfered.
   */

  reg [BURSTS_PER_TRANSFER_WIDTH-1:0] burst_count = 'h00;
  reg [BURSTS_PER_TRANSFER_WIDTH-1:0] cur_burst_length = 'h00;
  reg [ID_WIDTH-1:0] id;
  wire [ID_WIDTH-1:0] id_next = inc_id(id);
  wire incr_en;
  wire incr_id;

  assign eot = burst_count == 'h00;
  assign request_id = id;

  assign incr_en = (response_id != id_next) && (enable == 1'b1);
  assign incr_id = (state == STATE_GEN_ID) && (incr_en == 1'b1);

  always @(posedge clk) begin
    if (state == STATE_IDLE) begin
      burst_count <= req_burst_count;
    end else if (state == STATE_REWIND_ID) begin
      burst_count <= cur_burst_length;
    end else if (incr_id == 1'b1) begin
      burst_count <= burst_count - 1'b1;
    end
  end
  always @(posedge clk) begin
    if (req_ready == 1'b1 & req_valid == 1'b1) begin
      cur_req_xlast <= req_xlast;
      cur_burst_length <= req_burst_count;
    end
  end

  always @(posedge clk) begin
    if (resetn == 1'b0) begin
      id <= 'h0;
    end else if (state == STATE_REWIND_ID) begin
      id <= rew_id;
    end else if (incr_id == 1'b1) begin
      id <= id_next;
    end
  end

  always @(posedge clk) begin
    if (resetn == 1'b0) begin
      req_ready <= 1'b0;
    end else begin
      req_ready <= (nx_state == STATE_IDLE || nx_state == STATE_CONSUME);
    end
  end

  assign transfer_id_match = cur_transfer_id == rew_transfer_id[0];

  always @(posedge clk) begin
    if (resetn == 1'b0) begin
      cur_transfer_id <= 1'b0;
    end else if (req_valid == 1'b1 && req_ready == 1'b1) begin
      cur_transfer_id <= ~cur_transfer_id;
    end
  end

  /*
   * Once rewind request is received we need to stop incrementing the burst ID.
   *
   * If the current segment matches the segment that was interrupted and
   * if it was a last segment we ignore consecutive segments until the last
   * segment is received, in other case we can jump to the next segment.
   *
   * If the current segment is newer than the one got interrupted and the
   * interrupted one was a last segment we need to replay the current
   * segment with the adjusted burst ID. If the interrupted segment was not last
   * we need to consume/ignore all segments until a last segment is received.
   *
   * Completion requests are generated for every segment that is
   * consumed/ignored. These are handled by the response_manager once the
   * interrupted segment got transferred to the destination.
   */
  always @(*) begin
    nx_state = state;
    nx_completion_req_valid = 0;
    case (state)
      STATE_IDLE: begin
        if (rewind_req_valid == 1'b1 && rewind_req_ready == 1'b1) begin
          nx_state = STATE_REWIND_ID;
        end else if (req_valid == 1'b1) begin
          nx_state = STATE_GEN_ID;
        end
      end
      STATE_GEN_ID: begin
        if (rewind_req_valid == 1'b1 && rewind_req_ready == 1'b1) begin
          nx_state = STATE_REWIND_ID;
        end else if (eot == 1'b1 && incr_en == 1'b1) begin
          nx_state = STATE_IDLE;
        end
      end
      STATE_REWIND_ID: begin
        if (transfer_id_match) begin
          if (rew_req_xlast) begin
            nx_state = STATE_IDLE;
          end else begin
            nx_state = STATE_CONSUME;
          end
        end else begin
          if (rew_req_xlast) begin
            nx_state = STATE_GEN_ID;
          end else if (cur_req_xlast) begin
            nx_state = STATE_IDLE;
            nx_completion_req_valid = 1;
          end else begin
            nx_state = STATE_CONSUME;
            nx_completion_req_valid = 1;
          end
        end
      end
      STATE_CONSUME: begin
        if (req_valid) begin
          nx_completion_req_valid = 1;
          nx_state = STATE_WAIT_LAST;
        end
      end
      STATE_WAIT_LAST:begin
        if (cur_req_xlast) begin
          nx_state = STATE_IDLE;
        end else begin
          nx_state = STATE_CONSUME;
        end
      end

      default: begin
        nx_state = STATE_IDLE;
      end
    endcase
  end

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

  always @(posedge clk) begin
    if (rewind_req_valid == 1'b1 && rewind_req_ready == 1'b1) begin
      {rew_transfer_id, rew_req_xlast, rew_id} <= rewind_req_data;
    end
  end

  always @(posedge clk) begin
    if (resetn == 1'b0) begin
      completion_req_valid <= 1'b0;
    end else begin
      completion_req_valid <= nx_completion_req_valid;
    end
  end
  assign completion_req_last = cur_req_xlast;
  assign completion_transfer_id = rew_transfer_id;

  assign rewind_state = (state == STATE_REWIND_ID);
  assign rewind_req_ready = completion_req_ready;

  assign abort_req = (state == STATE_REWIND_ID) && !rew_req_xlast && !cur_req_xlast;

endmodule