// ***************************************************************************
// ***************************************************************************
// Copyright 2011(c) Analog Devices, Inc.
//
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// ***************************************************************************
// ***************************************************************************

`timescale 1ns/100ps

module fmcadc2_spi (

  input                   spi_adf4355,
  input                   spi_adf4355_ce,

  input                   spi_clk,
  input       [ 2:0]      spi_csn,
  input                   spi_mosi,
  output                  spi_miso,

  output                  spi_adc_csn,
  output                  spi_adc_clk,
  inout                   spi_adc_sdio,

  output                  spi_adf4355_data_or_csn_0,
  output                  spi_adf4355_clk_or_csn_1,
  output                  spi_adf4355_le_or_clk,
  inout                   spi_adf4355_ce_or_sdio);

  // internal registers

  reg     [ 5:0]  spi_count = 'd0;
  reg             spi_rd_wr_n = 'd0;
  reg             spi_enable = 'd0;

  // internal signals

  wire            spi_csn_s;
  wire            spi_enable_s;

  // check on rising edge and change on falling edge

  assign spi_csn_s = & spi_csn;
  assign spi_enable_s = spi_enable & ~spi_csn_s;

  always @(posedge spi_clk or posedge spi_csn_s) begin
    if (spi_csn_s == 1'b1) begin
      spi_count <= 6'd0;
      spi_rd_wr_n <= 1'd0;
    end else begin
      spi_count <= (spi_count < 6'h3f) ? spi_count + 1'b1 : spi_count;
      if (spi_count == 6'd0) begin
        spi_rd_wr_n <= spi_mosi;
      end
    end
  end

  always @(negedge spi_clk or posedge spi_csn_s) begin
    if (spi_csn_s == 1'b1) begin
      spi_enable <= 1'b0;
    end else begin
      if (spi_count == 6'd16) begin
        spi_enable <= spi_rd_wr_n;
      end
    end
  end

  assign spi_miso = ((spi_adc_sdio & ~spi_csn[0]) | (~spi_adf4355 &
    spi_adf4355_ce_or_sdio & ~(spi_csn[1] & spi_csn[2])));

  // adc interface (3 wire)

  assign spi_adc_csn = spi_csn[0];
  assign spi_adc_clk = spi_clk;
  assign spi_adc_sdio = (spi_enable_s == 1'b0) ? spi_mosi : 1'bz;

  // adf4355 or normal (AMP/EXT)

  assign spi_adf4355_data_or_csn_0 = (spi_adf4355 == 1'b1) ? spi_mosi : spi_csn[1];
  assign spi_adf4355_clk_or_csn_1 = (spi_adf4355 == 1'b1) ? spi_clk : spi_csn[2];
  assign spi_adf4355_le_or_clk = (spi_adf4355 == 1'b1) ? spi_csn[1] : spi_clk;
  assign spi_adf4355_ce_or_sdio = (spi_adf4355 == 1'b1) ? spi_adf4355_ce :
    ((spi_enable_s == 1'b0) ? spi_mosi : 1'bz);

endmodule

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