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

//

// Filename:    zipcounter.v

//

// Project:     Zip CPU -- a small, lightweight, RISC CPU soft core

//

// Purpose:

//              A very, _very_ simple counter.  It's purpose doesn't really

//      include rollover, but it will interrupt on rollover.  It can be set,

//      although my design concept is that it can be reset.  It cannot be

//      halted.  It will always produce interrupts--whether or not they are 

//      handled interrupts is another question--that's up to the interrupt

//      controller.

//

//      My intention is to use this counter for process accounting: I should

//      be able to use this to count clock ticks of processor time assigned to

//      each task by resetting the counter at the beginning of every task

//      interval, and reading the result at the end of the interval.  As long

//      as the interval is less than 2^32 clocks, there should be no problem.

//      Similarly, this can be used to measure CPU wishbone bus stalls, 

//      prefetch stalls, or other CPU stalls (i.e. stalling as part of a JMP

//      instruction, or a read from the condition codes following a write).

//

//

// Creator:     Dan Gisselquist, Ph.D.

//              Gisselquist Technology, LLC

//

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

//

// Copyright (C) 2015-2016, Gisselquist Technology, LLC

//

// This program is free software (firmware): you can redistribute it and/or

// modify it under the terms of  the GNU General Public License as published

// by the Free Software Foundation, either version 3 of the License, or (at

// your option) any later version.

//

// This program is distributed in the hope that it will be useful, but WITHOUT

// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or

// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

// for more details.

//

// License:     GPL, v3, as defined and found on www.gnu.org,

//              http://www.gnu.org/licenses/gpl.html

//

//

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

//

module  zipcounter(i_clk, i_ce,

                i_wb_cyc, i_wb_stb, i_wb_we, i_wb_data,

                        o_wb_ack, o_wb_stall, o_wb_data,

                o_int);

        parameter       BW = 32;

        input                           i_clk, i_ce;

        // Wishbone inputs

        input                           i_wb_cyc, i_wb_stb, i_wb_we;

        input           [(BW-1):0]       i_wb_data;

        // Wishbone outputs

        output  reg                     o_wb_ack;

        output  wire                    o_wb_stall;

        output  reg     [(BW-1):0]       o_wb_data;

        // Interrupt line

        output  reg                     o_int;

        initial o_int = 0;

        initial o_wb_data = 32'h00;

        always @(posedge i_clk)

                if ((i_wb_cyc)&&(i_wb_stb)&&(i_wb_we))

                        { o_int, o_wb_data } <= { 1'b0, i_wb_data };

                else if (i_ce)

                        { o_int, o_wb_data } <= o_wb_data+{{(BW-1){1'b0}},1'b1};

                else

                        o_int <= 1'b0;

        initial o_wb_ack = 1'b0;

        always @(posedge i_clk)

                o_wb_ack <= (i_wb_cyc)&&(i_wb_stb);

        assign  o_wb_stall = 1'b0;

endmodule