// ***************************************************************************
// ***************************************************************************
// Copyright (C) 2022-2023 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
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// 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:
//
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//      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>
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//
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//      This will allow to generate bit files and not release the source code,
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//
// ***************************************************************************
// ***************************************************************************

`timescale 1ns/100ps

module axi_ad3552r_if (

  input                   clk_in,  // 120MHz
  input                   reset_in,
  input       [31:0]      dac_data,
  input                   dac_data_valid,
  input                   dac_data_valid_ext,
  output                  dac_data_ready,

  input       [ 7:0]      address,
  input       [23:0]      data_write,
  input                   sdr_ddr_n,
  input                   symb_8_16b,
  input                   transfer_data,
  input                   stream,
  input                   external_sync,
  input                   external_sync_arm,

  output                  if_busy,
  output                  sync_ext_device,
  output reg  [23:0]      data_read,

  // DAC control signals

  output                  sclk,
  output reg              csn,
  input       [ 3:0]      sdio_i,
  output      [ 3:0]      sdio_o,
  output                  sdio_t
);

  wire            transfer_data_s;
  wire            start_synced;
  wire   [31:0]   dac_data_int;
  wire            dac_data_valid_synced;
  wire            external_sync_s;

  reg    [55:0]   transfer_reg        = 56'h0;
  reg    [15:0]   counter             = 16'h0;
  reg    [ 2:0]   transfer_state      = 0;
  reg    [ 2:0]   transfer_state_next = 0;
  reg             cycle_done          = 1'b0;
  reg             transfer_step       = 1'b0;
  reg             sclk_ddr            = 1'b0;
  reg             full_speed          = 1'b0;
  reg             transfer_data_d     = 1'b0;
  reg             transfer_data_dd    = 1'b0;
  reg    [ 3:0]   valid_captured_d    = 4'b0;
  reg             data_r_wn           = 1'b0;
  reg             valid_captured      = 1'b0;
  reg             start_transfer      = 1'b0;
  reg             if_busy_reg         = 1'b0;
  reg             dac_data_ready_s    = 1'b0;
  reg             external_sync_arm_reg = 1'b0;
  reg             external_sync_reg = 1'b0;

  localparam  [ 2:0]  IDLE = 3'h0,
                      CS_LOW = 3'h1,
                      WRITE_ADDRESS = 3'h2,
                      TRANSFER_REGISTER = 3'h3,
                      READ_REGISTER = 3'h4,
                      STREAM = 3'h5,
                      CS_HIGH = 3'h6;

  assign if_busy = if_busy_reg;

  // transform the transfer data rising edge into a pulse

  assign transfer_data_s = transfer_data_d & ~transfer_data_dd;

  // start the data stream transfer after valid has been captured

  assign start_synced = valid_captured_d[1] & start_transfer & stream;
  assign sync_ext_device = start_synced ;

  // use dac_data valid from an external source only if external_sync_arm_reg is 1

  assign dac_data_valid_synced = (external_sync_arm_reg == 1'b1) ? (dac_data_valid & dac_data_valid_ext) : dac_data_valid ;
  assign dac_data_ready = dac_data_ready_s & dac_data_valid_synced;
  assign dac_data_int = dac_data;

  // sync the data only if the synchronizations has been armed in software

  assign external_sync_s =  ~external_sync_arm_reg | external_sync_reg;

  always @(posedge clk_in) begin
    if(reset_in == 1'b1) begin
      transfer_data_d  <= 'd0;
      transfer_data_dd <= 'd0;
      valid_captured_d <= 4'b0;
      valid_captured   <= 1'b0;
    end else begin
      transfer_data_d  <= transfer_data;
      transfer_data_dd <= transfer_data_d;
      valid_captured_d <= {valid_captured_d[2:0], valid_captured};
    end
    if(transfer_state == CS_HIGH || stream == 1'b0) begin
      start_transfer <= 1'b0;
      valid_captured <= 1'b0;
      valid_captured_d <= 4'b0;
    end

   // pulse to level conversion

    if(external_sync_arm == 1'b1) begin
      external_sync_arm_reg <= 1'b1;
    end
    if(external_sync == 1'b1) begin
      external_sync_reg <= 1'b1;
    end

    if(transfer_state == CS_HIGH) begin
      external_sync_arm_reg <= 1'b0;
      external_sync_reg <= 1'b0;
    end

    if(dac_data_valid == 1'b1 && start_transfer == 1'b1) begin
      valid_captured <= 1'b1;
    end
    if(transfer_data == 1'b1) begin
      start_transfer <= 1'b1;
    end

  end

  always @(posedge clk_in) begin
    if (reset_in == 1'b1) begin
      transfer_state <= IDLE;
    end else begin
      transfer_state <= transfer_state_next;
    end
  end

  // FSM next state logic

  always @(*) begin
    case (transfer_state)
      IDLE : begin
        // goes in to the next state only if the control is to transfer register or synced transfer(if it's armed in software)
        transfer_state_next = ((transfer_data_s == 1'b1 && stream == 1'b0) || (start_synced == 1'b1 && external_sync_s))  ? CS_LOW : IDLE;
        csn = 1'b1;
        transfer_step = 0;
        cycle_done = 0;
      end
      CS_LOW : begin
        // brings CS down
        // loads all configuration
        // puts data on the SDIO pins
        // needs 5 ns before risedge of the clock
        transfer_state_next = WRITE_ADDRESS;
        csn = 1'b0;
        transfer_step = 0;
        cycle_done = 0;
      end
      WRITE_ADDRESS : begin
        // writes the address
        // it works either at full speed (60 MHz) when streaming or normal
        // speed (15 MHz)
        // full speed - 2 clock cycles
        // half speed 8 clock cycles
        cycle_done = full_speed ? (counter == 16'h3) : (counter == 16'hf);
        transfer_state_next = cycle_done ? (stream ? STREAM : TRANSFER_REGISTER) : WRITE_ADDRESS ;
        csn = 1'b0;
        // in streaming, change data on falledge. On regular transfer, change data on negedge.
        //A single step should be done for 8 bit addressing
        transfer_step = full_speed ? (counter[0]== 1'h1) : ((counter[4:0] == 5'h5));
      end
      TRANSFER_REGISTER : begin
        // always works at 15 MHz
        // can be DDR or SDR
        cycle_done = sdr_ddr_n ? (symb_8_16b ? (counter == 16'h10) : (counter == 16'h20))  :
                                 (symb_8_16b ? (counter == 16'h09) : (counter == 16'h11));
        transfer_state_next = cycle_done ? CS_HIGH : TRANSFER_REGISTER;
        csn = 1'b0;
        // in DDR mode, change data on falledge
        transfer_step = sdr_ddr_n ? (counter[2:0] == 3'h0) :   (counter[1:0] == 2'h0);
      end
      STREAM : begin
        // can be DDR or SDR
        // in DDR mode needs to be make sure the clock and data is shifted by 2 ns
        cycle_done = stream ? (sdr_ddr_n ? (counter == 16'h0f) : (counter == 16'h7)):
                              (sdr_ddr_n ? (counter == 16'h10) : (counter == 16'h7));
        transfer_state_next = (stream && external_sync_s) ? STREAM: ((cycle_done || external_sync_s == 1'b0) ?  CS_HIGH :STREAM);
        csn = 1'b0;
        transfer_step = sdr_ddr_n ? counter[0] :  1'b1;
      end
      CS_HIGH : begin
        cycle_done = 1'b1;
        transfer_state_next = cycle_done ? IDLE : CS_HIGH;
        csn = 1'b1;
        transfer_step = 0;
      end
      default : begin
        cycle_done = 0;
        transfer_state_next = IDLE;
        csn = 1'b1;
        transfer_step = 0;
      end
    endcase
  end

  // counter is used to time all states
  // depends on number of clock cycles per phase

  always @(posedge clk_in) begin
    if (transfer_state == IDLE || reset_in == 1'b1) begin
      counter <= 'b0;
    end else if (transfer_state == WRITE_ADDRESS | transfer_state == TRANSFER_REGISTER | transfer_state == STREAM) begin
      if (cycle_done) begin
        counter <= 0;
      end else  begin
        counter <= counter + 1;
      end
    end
  end

  always @(negedge clk_in) begin
    if (transfer_state == STREAM | transfer_state == WRITE_ADDRESS) begin
      sclk_ddr <= !sclk_ddr;
    end else begin
      sclk_ddr <= 0;
    end
  end

  // selection between 60 MHz and 15 MHz

  assign sclk = full_speed ? (sdr_ddr_n ? counter[0] : sclk_ddr) : counter[2];

  always @(posedge clk_in) begin
    if (transfer_state == CS_LOW) begin
      data_r_wn <= address[7];
    end else if (transfer_state == CS_HIGH) begin
      data_r_wn <=1'b0;
    end
    if (transfer_state == STREAM) begin
      if (cycle_done == 1'b1) begin
        dac_data_ready_s <= stream;
      end else begin
        dac_data_ready_s <= 1'b0;
      end
    end else begin
      dac_data_ready_s <= 1'b0;
    end
    if (transfer_state == CS_LOW) begin
      full_speed = stream;
      if(stream) begin
        transfer_reg <= {address,dac_data_int, 16'h0};
      end else begin
        transfer_reg <= {address,data_write, 24'h0};
      end
    end else if ((transfer_state == STREAM & cycle_done) || (transfer_state != STREAM  && transfer_state_next == STREAM)) begin
      transfer_reg <= {dac_data_int, 24'h0};
    end else if (transfer_step && transfer_state != CS_HIGH) begin
      transfer_reg <= {transfer_reg[51:0], sdio_i};
    end

    if (transfer_state == CS_HIGH) begin
      if (symb_8_16b == 1'b0) begin
        data_read <= {8'h0,transfer_reg[15:0]};
      end else begin
        data_read <= {16'h0,transfer_reg[7:0]};
      end
    end else begin
      data_read <= data_read;
    end
    if (transfer_state == CS_HIGH || transfer_state == IDLE) begin
      if_busy_reg <= 1'b0;
    end else begin
      if_busy_reg <= 1'b1;
    end
  end

  // address[7] is r_wn : depends also on the state machine, input only when
  // in TRANSFER register mode

  assign sdio_t = (data_r_wn & transfer_state == TRANSFER_REGISTER);
  assign sdio_o = transfer_reg[55:52];

endmodule