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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: omsp_watchdog.v

// 

// *Module Description:

//                       Watchdog Timer

//

// *Author(s):

//              - Olivier Girard,    olgirard@gmail.com

//

//----------------------------------------------------------------------------

// $Rev: 34 $

// $LastChangedBy: olivier.girard $

// $LastChangedDate: 2009-12-29 20:10:34 +0100 (Tue, 29 Dec 2009) $

//----------------------------------------------------------------------------

`include "timescale.v"

`include "openMSP430_defines.v"

module  omsp_watchdog (

// OUTPUTs

    nmi_evt,                        // NMI Event

    per_dout,                       // Peripheral data output

    wdtifg_set,                     // Set Watchdog-timer interrupt flag

    wdtpw_error,                    // Watchdog-timer password error

    wdttmsel,                       // Watchdog-timer mode select

// INPUTs

    aclk_en,                        // ACLK enable

    dbg_freeze,                     // Freeze Watchdog counter

    mclk,                           // Main system clock

    nmi,                            // Non-maskable interrupt (asynchronous)

    nmie,                           // Non-maskable interrupt enable

    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

    smclk_en,                       // SMCLK enable

    wdtie                           // Watchdog timer interrupt enable

);

// OUTPUTs

//=========

output              nmi_evt;        // NMI Event

output       [15:0] per_dout;       // Peripheral data output

output              wdtifg_set;     // Set Watchdog-timer interrupt flag

output              wdtpw_error;    // Watchdog-timer password error

output              wdttmsel;       // Watchdog-timer mode select

// INPUTs

//=========

input               aclk_en;        // ACLK enable

input               dbg_freeze;     // Freeze Watchdog counter

input               mclk;           // Main system clock

input               nmi;            // Non-maskable interrupt (asynchronous)

input               nmie;           // Non-maskable interrupt enable

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

input               smclk_en;       // SMCLK enable

input               wdtie;          // Watchdog timer interrupt enable

//=============================================================================

// 1)  PARAMETER DECLARATION

//=============================================================================

// Register addresses

parameter           WDTCTL     = 9'h120;

// Register one-hot decoder

parameter           WDTCTL_D   = (512'h1 << WDTCTL);

//============================================================================

// 2)  REGISTER DECODER

//============================================================================

// Register address decode

reg  [511:0]  reg_dec;

always @(per_addr)

  case ({per_addr,1'b0})

    WDTCTL :     reg_dec  =  WDTCTL_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

//============================================================================

// WDTCTL Register

//-----------------

// WDTNMI & WDTSSEL are not implemented and therefore masked

reg  [7:0] wdtctl;

wire       wdtctl_wr = reg_wr[WDTCTL];

always @ (posedge mclk or posedge puc)

  if (puc)            wdtctl <=  8'h00;

  else if (wdtctl_wr) wdtctl <=  per_din[7:0] & 8'hd7;

wire       wdtpw_error = wdtctl_wr & (per_din[15:8]!=8'h5a);

wire       wdttmsel    = wdtctl[4];

//============================================================================

// 3) REGISTERS

//============================================================================

// Data output mux

wire [15:0] wdtctl_rd  = {8'h69, wdtctl}  & {16{reg_rd[WDTCTL]}};

wire [15:0] per_dout   =  wdtctl_rd;

//=============================================================================

// 4)  NMI GENERATION

//=============================================================================

// Synchronization state

reg [2:0] nmi_sync;

always @ (posedge mclk or posedge puc)

  if (puc)  nmi_sync <= 3'h0;

  else      nmi_sync <= {nmi_sync[1:0], nmi};

// Edge detection

wire        nmi_re    = ~nmi_sync[2] &  nmi_sync[0] & nmie;

wire        nmi_fe    =  nmi_sync[2] & ~nmi_sync[0] & nmie;

// NMI event

wire        nmi_evt   = wdtctl[6] ? nmi_fe : nmi_re;

//=============================================================================

// 5)  WATCHDOG TIMER

//=============================================================================

// Watchdog clock source selection

//---------------------------------

wire  clk_src_en = wdtctl[2] ? aclk_en : smclk_en;

// Watchdog 16 bit counter

//--------------------------

reg [15:0] wdtcnt;

wire       wdtcnt_clr = (wdtctl_wr & per_din[3]) | wdtifg_set;

always @ (posedge mclk or posedge puc)

  if (puc)                                        wdtcnt <= 16'h0000;

  else if (wdtcnt_clr)                            wdtcnt <= 16'h0000;

  else if (~wdtctl[7] & clk_src_en & ~dbg_freeze) wdtcnt <= wdtcnt+16'h0001;

// Interval selection mux

//--------------------------

reg        wdtqn;

always @(wdtctl or wdtcnt)

    case(wdtctl[1:0])

      2'b00  : wdtqn =  wdtcnt[15];

      2'b01  : wdtqn =  wdtcnt[13];

      2'b10  : wdtqn =  wdtcnt[9];

      default: wdtqn =  wdtcnt[6];

    endcase

// Watchdog event detection

//-----------------------------

reg        wdtqn_dly;

always @ (posedge mclk or posedge puc)

  if (puc) wdtqn_dly <= 1'b0;

  else     wdtqn_dly <= wdtqn;

wire       wdtifg_set =  (~wdtqn_dly & wdtqn) | wdtpw_error;

endmodule // omsp_watchdog

`include "openMSP430_undefines.v"