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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_dbg_uart.v

// 

// *Module Description:

//                       Debug UART communication interface (8N1, Half-duplex)

//

// *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_dbg_uart (

// OUTPUTs

    dbg_addr,                       // Debug register address

    dbg_din,                        // Debug register data input

    dbg_rd,                         // Debug register data read

    dbg_uart_txd,                   // Debug interface: UART TXD

    dbg_wr,                         // Debug register data write

// INPUTs

    dbg_dout,                       // Debug register data output

    dbg_rd_rdy,                     // Debug register data is ready for read

    dbg_uart_rxd,                   // Debug interface: UART RXD

    mclk,                           // Main system clock

    mem_burst,                      // Burst on going

    mem_burst_end,                  // End TX/RX burst

    mem_burst_rd,                   // Start TX burst

    mem_burst_wr,                   // Start RX burst

    mem_bw,                         // Burst byte width

    por                             // Power on reset

);

// OUTPUTs

//=========

output        [5:0] dbg_addr;       // Debug register address

output       [15:0] dbg_din;        // Debug register data input

output              dbg_rd;         // Debug register data read

output              dbg_uart_txd;   // Debug interface: UART TXD

output              dbg_wr;         // Debug register data write

// INPUTs

//=========

input        [15:0] dbg_dout;       // Debug register data output

input               dbg_rd_rdy;     // Debug register data is ready for read

input               dbg_uart_rxd;   // Debug interface: UART RXD

input               mclk;           // Main system clock

input               mem_burst;      // Burst on going

input               mem_burst_end;  // End TX/RX burst

input               mem_burst_rd;   // Start TX burst

input               mem_burst_wr;   // Start RX burst

input               mem_bw;         // Burst byte width

input               por;            // Power on reset

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

// 1)  UART RECEIVE LINE SYNCHRONIZTION & FILTERING

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

// Synchronize RXD input & buffer

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

reg  [3:0] rxd_sync;

always @ (posedge mclk or posedge por)

  if (por) rxd_sync <=  4'h0;

  else     rxd_sync <=  {rxd_sync[2:0], dbg_uart_rxd};

// Majority decision

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

reg        rxd_maj;

wire [1:0] rxd_maj_cnt = {1'b0, rxd_sync[1]} +

                         {1'b0, rxd_sync[2]} +

                         {1'b0, rxd_sync[3]};

wire       rxd_maj_nxt = (rxd_maj_cnt>=2'b10);

always @ (posedge mclk or posedge por)

  if (por) rxd_maj <=  1'b0;

  else     rxd_maj <=  rxd_maj_nxt;

wire rxd_s  =  rxd_maj;

wire rxd_fe =  rxd_maj & ~rxd_maj_nxt;

wire rxd_re = ~rxd_maj &  rxd_maj_nxt;

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

// 2)  UART STATE MACHINE

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

// Receive state

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

reg  [2:0] uart_state;

reg  [2:0] uart_state_nxt;

wire       sync_done;

wire       xfer_done;

reg [19:0] xfer_buf;

// State machine definition

parameter  RX_SYNC  = 3'h0;

parameter  RX_CMD   = 3'h1;

parameter  RX_DATA1 = 3'h2;

parameter  RX_DATA2 = 3'h3;

parameter  TX_DATA1 = 3'h4;

parameter  TX_DATA2 = 3'h5;

// State transition

always @(uart_state or xfer_buf or mem_burst or mem_burst_wr or mem_burst_rd or mem_burst_end or mem_bw)

  case (uart_state)

    RX_SYNC  : uart_state_nxt =  RX_CMD;

    RX_CMD   : uart_state_nxt =  mem_burst_wr                ?

                                (mem_bw                      ? RX_DATA2 : RX_DATA1) :

                                 mem_burst_rd                ?

                                (mem_bw                      ? TX_DATA2 : TX_DATA1) :

                                (xfer_buf[`DBG_UART_WR]      ?

                                (xfer_buf[`DBG_UART_BW]      ? RX_DATA2 : RX_DATA1) :

                                (xfer_buf[`DBG_UART_BW]      ? TX_DATA2 : TX_DATA1));

    RX_DATA1 : uart_state_nxt =  RX_DATA2;

    RX_DATA2 : uart_state_nxt = (mem_burst & ~mem_burst_end) ?

                                (mem_bw                      ? RX_DATA2 : RX_DATA1) :

                                 RX_CMD;

    TX_DATA1 : uart_state_nxt =  TX_DATA2;

    TX_DATA2 : uart_state_nxt = (mem_burst & ~mem_burst_end) ?

                                (mem_bw                      ? TX_DATA2 : TX_DATA1) :

                                 RX_CMD;

    default  : uart_state_nxt =  RX_CMD;

  endcase

// State machine

always @(posedge mclk or posedge por)

  if (por)                              uart_state <= RX_SYNC;

  else if (xfer_done    | sync_done |

           mem_burst_wr | mem_burst_rd) uart_state <= uart_state_nxt;

// Utility signals

wire cmd_valid = (uart_state==RX_CMD) & xfer_done;

wire tx_active = (uart_state==TX_DATA1) | (uart_state==TX_DATA2);

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

// 3)  UART SYNCHRONIZATION

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

// After POR, the host needs to fist send a synchronization character (0x80)

// If this feature doesn't work properly, it is possible to disable it by

// commenting the DBG_UART_AUTO_SYNC define in the openMSP430.inc file.

reg        sync_busy;

always @ (posedge mclk or posedge por)

  if (por)                                 sync_busy <=  1'b0;

  else if ((uart_state==RX_SYNC) & rxd_fe) sync_busy <=  1'b1;

  else if ((uart_state==RX_SYNC) & rxd_re) sync_busy <=  1'b0;

assign sync_done =  (uart_state==RX_SYNC) & rxd_re & sync_busy;

`ifdef DBG_UART_AUTO_SYNC

reg [14:0] sync_cnt;

always @ (posedge mclk or posedge por)

  if (por)            sync_cnt <=  15'h7ff8;

  else if (sync_busy) sync_cnt <=  sync_cnt+15'h0001;

wire [11:0] bit_cnt_max = sync_cnt[14:3];

`else

wire [11:0] bit_cnt_max = `DBG_UART_CNT;

`endif

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

// 4)  UART RECEIVE / TRANSMIT

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

// Transfer counter

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

reg  [3:0] xfer_bit;

reg [11:0] xfer_cnt;

wire       txd_start    = dbg_rd_rdy | (xfer_done & (uart_state==TX_DATA1));

wire       rxd_start    = (xfer_bit==4'h0) & rxd_fe & ((uart_state!=RX_SYNC));

wire       xfer_bit_inc = (xfer_bit!=4'h0) & (xfer_cnt==12'h000);

assign     xfer_done    = (xfer_bit==4'hb);

always @ (posedge mclk or posedge por)

  if (por)                           xfer_bit <=  4'h0;

  else if (txd_start | rxd_start)    xfer_bit <=  4'h1;

  else if (xfer_done)                xfer_bit <=  4'h0;

  else if (xfer_bit_inc)             xfer_bit <=  xfer_bit+4'h1;

always @ (posedge mclk or posedge por)

  if (por)                           xfer_cnt <=  12'h000;

  else if (rxd_start)                xfer_cnt <=  {1'b0, bit_cnt_max[11:1]};

  else if (txd_start | xfer_bit_inc) xfer_cnt <=  bit_cnt_max;

  else                               xfer_cnt <=  xfer_cnt+12'hfff;

// Receive/Transmit buffer

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

wire [19:0] xfer_buf_nxt =  {rxd_s, xfer_buf[19:1]};

always @ (posedge mclk or posedge por)

  if (por)               xfer_buf <=  18'h00000;

  else if (dbg_rd_rdy)   xfer_buf <=  {1'b1, dbg_dout[15:8], 2'b01, dbg_dout[7:0], 1'b0};

  else if (xfer_bit_inc) xfer_buf <=  xfer_buf_nxt;

// Generate TXD output

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

reg dbg_uart_txd;

always @ (posedge mclk or posedge por)

  if (por)                           dbg_uart_txd <=  1'b1;

  else if (xfer_bit_inc & tx_active) dbg_uart_txd <=  xfer_buf[0];

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

// 5) INTERFACE TO DEBUG REGISTERS

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

reg [5:0] dbg_addr;

 always @ (posedge mclk or posedge por)

  if (por)            dbg_addr <=  6'h00;

  else if (cmd_valid) dbg_addr <=  xfer_buf[`DBG_UART_ADDR];

reg       dbg_bw;

always @ (posedge mclk or posedge por)

  if (por)            dbg_bw   <=  1'b0;

  else if (cmd_valid) dbg_bw   <=  xfer_buf[`DBG_UART_BW];

wire        dbg_din_bw =  mem_burst  ? mem_bw : dbg_bw;

wire [15:0] dbg_din    =  dbg_din_bw ? {8'h00,           xfer_buf[18:11]} :

                                       {xfer_buf[18:11], xfer_buf[8:1]};

wire        dbg_wr     = (xfer_done & (uart_state==RX_DATA2));

wire        dbg_rd     = mem_burst ? (xfer_done & (uart_state==TX_DATA2)) :

                                     (cmd_valid & ~xfer_buf[`DBG_UART_WR]) | mem_burst_rd;

endmodule // omsp_dbg_uart

`include "openMSP430_undefines.v"