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////////////////////////////////////////////////////////////////////////////////
//
//  WISHBONE revB.2 compliant Programable Interrupt Timer - Control registers
//
//  Author: Bob Hayes
//          rehayes@opencores.org
//
//  Downloaded from: http://www.opencores.org/projects/pit.....
//
////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2011, Robert Hayes
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//     * Neither the name of the <organization> nor the
//       names of its contributors may be used to endorse or promote products
//       derived from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY Robert Hayes ''AS IS'' AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL Robert Hayes BE LIABLE FOR ANY
// DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
// ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
////////////////////////////////////////////////////////////////////////////////
// 45678901234567890123456789012345678901234567890123456789012345678901234567890

module pit_regs #(parameter COUNT_SIZE = 16,
                  parameter NO_PRESCALE = 1'b0,
                  parameter DWIDTH = 16)
  (
  output logic [COUNT_SIZE-1:0] mod_value,    // Main Counter Modulo Value
  output                 [ 3:0] pit_pre_scl,  // PIT Prescaler Value
  output logic                  pit_slave,    // PIT Slave Mode
  output logic                  pit_flg_clr,  // Clear PIT Rollover Flag
  output logic                  pit_ien,      // PIT Interrupt Enable
  output logic                  cnt_sync_o,   // PIT Counter Enable
  output logic                  pit_irq_o,    // PIT interrupt
  input                         bus_clk,      // Control register bus clock
  input                         async_rst_b,  // Async reset signal
  input                         sync_reset,   // Syncronous reset signal
  input                         pit_flag,     // PIT Rollover Flag
  input            [DWIDTH-1:0] write_bus,    // Write Data Bus
  input                  [ 3:0] write_regs,   // Write Register strobes
  input                         cnt_flag_o    // Counter Rollover Flag 
  );


  // registers
  logic [ 3:0] pit_pre;   // Optional register for PIT Prescale Counter modulo
                          //  This register should be removed durning synthesis
                          //  if the "NO_PRESCALE" parameter is set

  // Wires
  logic [15:0] write_data; // Data bus mux for 8 or 16 bit module bus

  //
  // module body
  //
  
  assign write_data = (DWIDTH == 8) ? {write_bus[7:0], write_bus[7:0]} : write_bus;
  
  assign pit_pre_scl = NO_PRESCALE ? 4'b0 : pit_pre;

  // generate wishbone write registers
  always_ff @(posedge bus_clk or negedge async_rst_b)
    if (!async_rst_b)
      begin
        pit_slave   <= 1'b0;
        pit_pre     <= 4'b0;
        pit_flg_clr <= 1'b0;
        pit_ien     <= 1'b0;
        cnt_sync_o  <= 1'b0;
        mod_value   <= 0;
       end
    else if (sync_reset)
      begin
        pit_slave   <= 1'b0;
        pit_pre     <= 4'b0;
        pit_flg_clr <= 1'b0;
        pit_ien     <= 1'b0;
        cnt_sync_o  <= 1'b0;
        mod_value   <= 0;
      end
    else
      case (write_regs) // synopsys parallel_case
         4'b0011 :  // 16-bit write
           begin
             pit_slave   <= write_data[15];
             pit_pre     <= write_data[11:8];
             pit_flg_clr <= write_data[2];
             pit_ien     <= write_data[1];
             cnt_sync_o  <= write_data[0];
           end
         4'b0001 :  // 8-bit low byte write
           begin
             pit_flg_clr <= write_data[2];
             pit_ien     <= write_data[1];
             cnt_sync_o  <= write_data[0];
           end
         4'b0010 :  // 8-bit high byte write
           begin
             pit_slave   <= write_data[7];
             pit_pre     <= write_data[3:0];
           end
         4'b1100 : mod_value        <= write_data;
         4'b0100 : mod_value[ 7:0]  <= write_data[7:0];
         4'b1000 : mod_value[15:8]  <= write_data[7:0];
         default:
           pit_flg_clr <= 1'b0;
      endcase

  // generate interrupt request signals
  always_ff @(posedge bus_clk or negedge async_rst_b)
    if (!async_rst_b)
      pit_irq_o <= 0;
    else if (sync_reset)
      pit_irq_o <= 0;
    else
      pit_irq_o <= cnt_flag_o && pit_ien; // interrupt signal is only generated
                                          //  when IEN (interrupt enable bit is set)


endmodule  // pit_regs