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//----------------------------------------------------------------------------
// Copyright (C) 2001 Authors
//
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// THE POSSIBILITY OF SUCH DAMAGE
//
//----------------------------------------------------------------------------
//
// *File Name: dac_spi_if.v
// 
// *Module Description:
//                       SPI interface for National's DAC121S101 12 bit DAC
//
// *Author(s):
//              - Olivier Girard,    olgirard@gmail.com
//
//----------------------------------------------------------------------------
// $Rev: 66 $
// $LastChangedBy: olivier.girard $
// $LastChangedDate: 2010-03-07 09:09:38 +0100 (Sun, 07 Mar 2010) $
//----------------------------------------------------------------------------
`include "timescale.v"
 
module  dac_spi_if (
 
// OUTPUTs
    cntrl1,                         // Control value 1
    cntrl2,                         // Control value 2
    din,                            // SPI Serial Data
    per_dout,                       // Peripheral data output
    sclk,                           // SPI Serial Clock
    sync_n,                         // SPI Frame synchronization signal (low active)
 
// INPUTs
    mclk,                           // Main system clock
    per_addr,                       // Peripheral address
    per_din,                        // Peripheral data input
    per_en,                         // Peripheral enable (high active)
    per_wen,                        // Peripheral write enable (high active)
    puc                             // Main system reset
);
 
// PARAMETERs
//============
parameter           SCLK_DIV  = 0;       // Serial clock divider (Tsclk=Tmclk*(SCLK_DIV+1)*2)
parameter           BASE_ADDR = 9'h190;  // Registers base address
 
// OUTPUTs
//=========
output        [3:0] cntrl1;         // Control value 1
output        [3:0] cntrl2;         // Control value 2
output              din;            // SPI Serial Data
output       [15:0] per_dout;       // Peripheral data output
output              sclk;           // SPI Serial Clock
output              sync_n;         // SPI Frame synchronization signal (low active)
 
// INPUTs
//=========
input               mclk;           // Main system clock
input         [7:0] per_addr;       // Peripheral address
input        [15:0] per_din;        // Peripheral data input
input               per_en;         // Peripheral enable (high active)
input         [1:0] per_wen;        // Peripheral write enable (high active)
input               puc;            // Main system reset
 
 
//=============================================================================
// 1)  PARAMETER DECLARATION
//=============================================================================
 
// Register addresses
parameter           DAC_VAL    = BASE_ADDR;
parameter           DAC_STAT   = BASE_ADDR+2;
parameter           CNTRL1     = BASE_ADDR+4;
parameter           CNTRL2     = BASE_ADDR+6;
 
 
// Register one-hot decoder
parameter           DAC_VAL_D  = (512'h1 << DAC_VAL);
parameter           DAC_STAT_D = (512'h1 << DAC_STAT);
parameter           CNTRL1_D   = (512'h1 << CNTRL1);
parameter           CNTRL2_D   = (512'h1 << CNTRL2);
 
 
//============================================================================
// 2)  REGISTER DECODER
//============================================================================
 
// Register address decode
reg  [511:0]  reg_dec; 
always @(per_addr)
  case ({per_addr,1'b0})
    DAC_VAL :     reg_dec  =  DAC_VAL_D;
    DAC_STAT:     reg_dec  =  DAC_STAT_D;
    CNTRL1  :     reg_dec  =  CNTRL1_D;
    CNTRL2  :     reg_dec  =  CNTRL2_D;
    default :     reg_dec  =  {512{1'b0}};
  endcase
 
// Read/Write probes
wire         reg_write =  |per_wen   & per_en;
wire         reg_read  = ~|per_wen   & per_en;
 
// Read/Write vectors
wire [511:0] reg_wr    = reg_dec & {512{reg_write}};
wire [511:0] reg_rd    = reg_dec & {512{reg_read}};
 
 
//============================================================================
// 3) REGISTERS
//============================================================================
 
// DAC_VAL Register
//------------------   
reg  [11:0] dac_val;
reg         dac_pd0;
reg         dac_pd1;
 
wire        dac_val_wr = reg_wr[DAC_VAL];
 
always @ (posedge mclk or posedge puc)
  if (puc)
    begin
       dac_val <= 12'h000;
       dac_pd0 <=  1'b0;
       dac_pd1 <=  1'b0;
    end
  else if (dac_val_wr)
    begin
       dac_val <=  per_din[11:0];
       dac_pd0 <=  per_din[12];
       dac_pd1 <=  per_din[13];
    end
 
 
// CNTRL1 Register
//------------------   
reg   [3:0] cntrl1;
 
wire        cntrl1_wr = reg_wr[CNTRL1];
 
always @ (posedge mclk or posedge puc)
  if (puc)            cntrl1 <=  4'h0;
  else if (cntrl1_wr) cntrl1 <=  per_din;
 
 
// CNTRL2 Register
//------------------   
reg   [3:0] cntrl2;
 
wire        cntrl2_wr = reg_wr[CNTRL2];
 
always @ (posedge mclk or posedge puc)
  if (puc)            cntrl2 <=  4'h0;
  else if (cntrl2_wr) cntrl2 <=  per_din;
 
 
 
//============================================================================
// 4) DATA OUTPUT GENERATION
//============================================================================
 
// Data output mux
wire [15:0] dac_val_rd  = { 2'b00,   dac_pd1, dac_pd0, dac_val} & {16{reg_rd[DAC_VAL]}};
wire [15:0] dac_stat_rd = {15'h0000, ~sync_n}                   & {16{reg_rd[DAC_STAT]}};
wire [15:0] cntrl1_rd   = {12'h000,  cntrl1}                    & {16{reg_rd[CNTRL1]}};
wire [15:0] cntrl2_rd   = {12'h000,  cntrl2}                    & {16{reg_rd[CNTRL2]}};
 
wire [15:0] per_dout    =  dac_val_rd   |
                           dac_stat_rd  |
                           cntrl1_rd    |
                           cntrl2_rd;
 
 
//============================================================================
// 5) SPI INTERFACE
//============================================================================
 
// SPI Clock divider
reg [3:0] spi_clk_div;
always @ (posedge mclk or posedge puc)
  if (puc)                 spi_clk_div <=  SCLK_DIV;
  else if (spi_clk_div==0) spi_clk_div <=  SCLK_DIV;
  else                     spi_clk_div <=  spi_clk_div-1;
 
// SPI Clock generation
reg       sclk;
always @ (posedge mclk or posedge puc)
  if (puc)                 sclk        <=  1'b0;
  else if (spi_clk_div==0) sclk        <=  ~sclk;
 
wire      sclk_re = (spi_clk_div==0) & ~sclk;
 
// SPI Transfer trigger
reg       spi_tfx_trig;
always @ (posedge mclk or posedge puc)
  if (puc)                   spi_tfx_trig <= 1'b0;
  else if (dac_val_wr)       spi_tfx_trig <= 1'b1;
  else if (sclk_re & sync_n) spi_tfx_trig <= 1'b0;
 
wire      spi_tfx_init = spi_tfx_trig & sync_n;
 
// Data counter
reg [3:0] spi_cnt;
wire      spi_cnt_done = (spi_cnt==4'hf);
always @ (posedge mclk or posedge puc)
  if (puc)                   spi_cnt <=  4'hf;
  else if (sclk_re)
    if (spi_tfx_init)        spi_cnt <=  4'he;
    else if (~spi_cnt_done)  spi_cnt <=  spi_cnt-1;
 
 
// Frame synchronization signal (low active)
reg sync_n;
always @ (posedge mclk or posedge puc)
  if (puc)                   sync_n  <=  1'b1;
  else if (sclk_re)
    if (spi_tfx_init)        sync_n  <=  1'b0;
    else if (spi_cnt_done)   sync_n  <=  1'b1;
 
 
// Value to be shifted_out
reg  [15:0] dac_shifter;
always @ (posedge mclk or posedge puc)
  if (puc)            dac_shifter <=  16'h000;
  else if (sclk_re)
    if (spi_tfx_init) dac_shifter <=  {2'b00, dac_pd1, dac_pd0, dac_val[11:0]};
    else              dac_shifter <=  {dac_shifter[14:0], 1'b0};
 
assign din = dac_shifter[15];
 
 
endmodule // dac_spi_if