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//////////////////////////////////////////////////////////////////////

////                                                              ////

////  ps2_keyboard_model.v                                        ////

////                                                              ////

////  This file is part of the "ps2" project                      ////

////  http://www.opencores.org/cores/ps2/                         ////

////                                                              ////

////  Author(s):                                                  ////

////      - mihad@opencores.org                                   ////

////      - Miha Dolenc                                           ////

////                                                              ////

////  All additional information is avaliable in the README.txt   ////

////  file.                                                       ////

////                                                              ////

////                                                              ////

//////////////////////////////////////////////////////////////////////

////                                                              ////

//// Copyright (C) 2000 Miha Dolenc, mihad@opencores.org          ////

////                                                              ////

//// 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, download it   ////

//// from http://www.opencores.org/lgpl.shtml                     ////

////                                                              ////

//////////////////////////////////////////////////////////////////////

//

// CVS Revision History

//

// $Log: not supported by cvs2svn $

//

`include "timescale.v"

module ps2_keyboard_model

(

    kbd_clk_io,

    kbd_data_io,

    last_char_received_o,

    char_valid_o

);

parameter [31:0] kbd_clk_period = 50000; // chould be between 33 and 50 us to generate the clock between 30 and 20 kHz

inout kbd_clk_io,

      kbd_data_io ;

output [7:0] last_char_received_o ;

reg    [7:0] last_char_received_o ;

output char_valid_o ;

reg    char_valid_o ;

reg kbd_clk,

    kbd_data ;

assign kbd_clk_io  = kbd_clk ? 1'bz : 1'b0 ;

assign kbd_data_io = kbd_data ? 1'bz : 1'b0 ;

reg receiving ;

initial

begin

    kbd_clk  = 1'b1 ;

    kbd_data = 1'b1 ;

    last_char_received_o = 0 ;

    char_valid_o         = 0 ;

    receiving = 0 ;

end

always@(kbd_data_io or kbd_clk_io)

begin

    // check if host is driving keyboard data low and doesn't drive clock

    if ( !kbd_data_io && kbd_data && kbd_clk_io)

    begin

        // wait for half of clock period

        #(kbd_clk_period/2) ;

        // state hasn't changed - host wishes to send data - go receiving

        if ( !kbd_data_io && kbd_data && kbd_clk_io)

            kbd_receive_char(last_char_received_o) ;

    end

end

task kbd_send_char ;

    input [7:0] char ;

    output      transmited_ok ;

    output      severe_error ;

    reg   [10:0] tx_reg ;

    integer i ;

begin:main

    severe_error  = 1'b0 ;

    transmited_ok = 1'b0 ;

    wait ( !receiving ) ;

    tx_reg = { 1'b1, !(^char), char, 1'b0 } ;

    fork

    begin:wait_for_idle

        wait( (kbd_clk_io === 1'b1) && (kbd_data_io === 1'b1) ) ;

    //    disable timeout ;

    end

    /*begin:timeout

        #(256 * kbd_clk_period) ;

        $display("Error! Keyboard bus did not go idle in 256 keyboard clock cycles time!") ;

        severe_error  = 1'b1 ;

        transmited_ok = 1'b0 ;

        disable main ;

    end*/

    join

    #(kbd_clk_period/2) ;

    if ( !kbd_clk_io )

    begin

        transmited_ok = 1'b0 ;

        kbd_data = 1'b1 ;

        disable main ;

    end

    i = 0 ;

    while ( i < 11 )

    begin

        kbd_data = tx_reg[i] ;

        #(kbd_clk_period/2) ;

        if ( !kbd_clk_io )

        begin

            transmited_ok = 1'b0 ;

            kbd_data = 1'b1 ;

            disable main ;

        end

        kbd_clk = 1'b0 ;

        i = i + 1 ;

        #(kbd_clk_period/2) ;

        kbd_clk = 1'b1 ;

    end

    if ( i == 11 )

        transmited_ok = 1'b1 ;

end

endtask // kbd_send_char

task kbd_receive_char;

    output [7:0] char ;

    reg          parity ;

    integer i ;

    reg          stop_bit_received ;

begin:main

    i = 0 ;

    stop_bit_received = 1 ;

    receiving = 1 ;

    #(kbd_clk_period/2) ;

    while ( i < 11 )

    begin

        if ( !kbd_clk_io )

        begin

            receiving = 0 ;

            disable main ;

        end

        kbd_clk = 1'b0 ;

        #(kbd_clk_period/2) ;

        kbd_clk = 1'b1 ;

        if ( i > 0 )

        begin

            if ( i <= 8 )

                char[i - 1] = kbd_data_io ;

            else if ( i == 9 )

            begin

                parity = kbd_data_io ;

                if ( parity !== ( !(^char) ) )

                    $display("Invalid parity bit received") ;

            end

            else

            begin

                if ( kbd_data_io !== 1'b1 )

                begin

                    i = i - 1 ;

                    stop_bit_received = 0 ;

                end

                else

                begin

                    kbd_data = 1'b0 ;

                end

            end

        end

        i = i + 1 ;

        #(kbd_clk_period/2) ;

    end

    if ( !kbd_clk_io )

    begin

        receiving = 0 ;

        disable main ;

    end

    kbd_clk  = 1'b0 ;

    #(kbd_clk_period/2) ;

    kbd_clk  <= 1'b1 ;

    kbd_data <= 1'b1 ;

    if ( stop_bit_received )

    begin

        char_valid_o = !char_valid_o ;

    end

    receiving = 0 ;

end

endtask // kbd_receive_char

endmodule // ps2_keyboard_model