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//----------------------------------------------------------------------------
// Copyright (C) 2001 Authors
//
// This source file may be used and distributed without restriction provided
// that this copyright statement is not removed from the file and that any
// derivative work contains the original copyright notice and the associated
// disclaimer.
//
// This source file is free software; you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published
// by the Free Software Foundation; either version 2.1 of the License, or
// (at your option) any later version.
//
// This source 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. See the GNU Lesser General Public
// License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with this source; if not, write to the Free Software Foundation,
// Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
//
//----------------------------------------------------------------------------
//
// *File Name: template_periph_8b.v
// 
// *Module Description:
//                       8 bit peripheral template.
//
// *Author(s):
//              - Olivier Girard,    olgirard@gmail.com
//
//----------------------------------------------------------------------------
`timescale 1ns / 100ps
 
module  template_periph_8b (
 
// OUTPUTs
    per_dout,                       // Peripheral data output
 
// 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
);
 
// OUTPUTs
//=========
output      [15:0] per_dout;        // Peripheral data output
 
// 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          CNTRL1    = 9'h090;
parameter          CNTRL2    = 9'h091;
parameter          CNTRL3    = 9'h092;
parameter          CNTRL4    = 9'h093;
 
 
// Register one-hot decoder
parameter          CNTRL1_D  = (256'h1 << (CNTRL1 /2));
parameter          CNTRL2_D  = (256'h1 << (CNTRL2 /2)); 
parameter          CNTRL3_D  = (256'h1 << (CNTRL3 /2)); 
parameter          CNTRL4_D  = (256'h1 << (CNTRL4 /2)); 
 
 
//============================================================================
// 2)  REGISTER DECODER
//============================================================================
 
// Register address decode
reg  [255:0]  reg_dec; 
always @(per_addr)
  case (per_addr)
    (CNTRL1 /2):   reg_dec   = CNTRL1_D;
    (CNTRL2 /2):   reg_dec   = CNTRL2_D;
    (CNTRL3 /2):   reg_dec   = CNTRL3_D;
    (CNTRL4 /2):   reg_dec   = CNTRL4_D;
    default    :   reg_dec   = {256{1'b0}};
  endcase
 
// Read/Write probes
wire         reg_lo_write =  per_wen[0] & per_en;
wire         reg_hi_write =  per_wen[1] & per_en;
wire         reg_read     = ~|per_wen   & per_en;
 
// Read/Write vectors
wire [255:0] reg_hi_wr    = reg_dec & {256{reg_hi_write}};
wire [255:0] reg_lo_wr    = reg_dec & {256{reg_lo_write}};
wire [255:0] reg_rd       = reg_dec & {256{reg_read}};
 
 
//============================================================================
// 3) REGISTERS
//============================================================================
 
// CNTRL1 Register
//-----------------
reg  [7:0] cntrl1;
 
wire       cntrl1_wr  = CNTRL1[0] ? reg_hi_wr[CNTRL1/2] : reg_lo_wr[CNTRL1/2];
wire [7:0] cntrl1_nxt = CNTRL1[0] ? per_din[15:8]       : per_din[7:0];
 
always @ (posedge mclk or posedge puc)
  if (puc)            cntrl1 <=  8'h00;
  else if (cntrl1_wr) cntrl1 <=  cntrl1_nxt;
 
 
// CNTRL2 Register
//-----------------
reg  [7:0] cntrl2;
 
wire       cntrl2_wr  = CNTRL2[0] ? reg_hi_wr[CNTRL2/2] : reg_lo_wr[CNTRL2/2];
wire [7:0] cntrl2_nxt = CNTRL2[0] ? per_din[15:8]       : per_din[7:0];
 
always @ (posedge mclk or posedge puc)
  if (puc)            cntrl2 <=  8'h00;
  else if (cntrl2_wr) cntrl2 <=  cntrl2_nxt;
 
 
// CNTRL3 Register
//-----------------
reg  [7:0] cntrl3;
 
wire       cntrl3_wr  = CNTRL3[0] ? reg_hi_wr[CNTRL3/2] : reg_lo_wr[CNTRL3/2];
wire [7:0] cntrl3_nxt = CNTRL3[0] ? per_din[15:8]       : per_din[7:0];
 
always @ (posedge mclk or posedge puc)
  if (puc)            cntrl3 <=  8'h00;
  else if (cntrl3_wr) cntrl3 <=  cntrl3_nxt;
 
 
// CNTRL4 Register
//-----------------
reg  [7:0] cntrl4;
 
wire       cntrl4_wr  = CNTRL4[0] ? reg_hi_wr[CNTRL4/2] : reg_lo_wr[CNTRL4/2];
wire [7:0] cntrl4_nxt = CNTRL4[0] ? per_din[15:8]       : per_din[7:0];
 
always @ (posedge mclk or posedge puc)
  if (puc)            cntrl4 <=  8'h00;
  else if (cntrl4_wr) cntrl4 <=  cntrl4_nxt;
 
 
 
//============================================================================
// 4) DATA OUTPUT GENERATION
//============================================================================
 
// Data output mux
wire [15:0] cntrl1_rd   = (cntrl1  & {8{reg_rd[CNTRL1/2]}})  << (8 & {4{CNTRL1[0]}});
wire [15:0] cntrl2_rd   = (cntrl2  & {8{reg_rd[CNTRL2/2]}})  << (8 & {4{CNTRL2[0]}});
wire [15:0] cntrl3_rd   = (cntrl3  & {8{reg_rd[CNTRL3/2]}})  << (8 & {4{CNTRL3[0]}});
wire [15:0] cntrl4_rd   = (cntrl4  & {8{reg_rd[CNTRL4/2]}})  << (8 & {4{CNTRL4[0]}});
 
wire [15:0] per_dout  =  cntrl1_rd  |
                         cntrl2_rd  |
                         cntrl3_rd  |
                         cntrl4_rd;
 
 
endmodule // template_periph_8b