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

//

// Filename:    rtcdate.v

//              

// Project:     A Wishbone Controlled Real--time Clock Core

//

// Purpose:

//      This core provides a real-time date function that can be coupled with

//      a real-time clock.  The date provided is in Binary Coded Decimal (bcd)

//      form, and available for reading and writing over the Wishbone Bus.

//

// WARNING: Race conditions exist when updating the date across the Wishbone

//      bus at or near midnight.  (This should be obvious, but it bears

//      stating.)  Specifically, if the update command shows up at the same

//      clock as the ppd clock, then the ppd clock will be ignored and the 

//      new date will be the date of the day following midnight.  However,

//      if the update command shows up one clock before the ppd, then the date

//      may be updated, but may have problems dealing with the last day of the

//      month or year.  To avoid race conditions, update the date sometime

//      after the stroke of midnight and before 5 clocks before the next

//      midnight.  If you are concerned that you might hit a race condition, 

//      just read the clock again (5+ clocks later) to make certain you set 

//      it correctly.

//

//

// Creator:     Dan Gisselquist, Ph.D.

//              Gisselquist Technology, LLC

//

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

//

// Copyright (C) 2015, 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.

//

// You should have received a copy of the GNU General Public License along

// with this program.  (It's in the $(ROOT)/doc directory.  Run make with no

// target there if the PDF file isn't present.)  If not, see

// <http://www.gnu.org/licenses/> for a copy.

//

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

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

//

//

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

module rtcdate(i_clk, i_ppd, i_wb_cyc, i_wb_stb, i_wb_we, i_wb_data,

                o_wb_ack, o_wb_stall, o_wb_data);

        input   i_clk;

        // A one part per day signal, i.e. basically a clock enable line that

        // controls when the beginning of the day happens.  This line should

        // be high on the very last second of any day in order for the rtcdate

        // module to always have the right date.

        input   i_ppd;

        // Wishbone inputs

        input   i_wb_cyc, i_wb_stb, i_wb_we;

        input   [31:0]   i_wb_data;

        // Wishbone outputs

        output  reg     o_wb_ack;

        output  wire    o_wb_stall;

        output  wire    [31:0]   o_wb_data;

        reg     [5:0]    r_day;

        reg     [4:0]    r_mon;

        reg     [13:0]   r_year;

        reg     last_day_of_month, last_day_of_year, is_leap_year;

        reg     [5:0]    days_per_month;

        initial days_per_month = 6'h31; // Remember, this is BCD

        always @(posedge i_clk)

        begin // Clock 3

                case(r_mon)

                5'h01: days_per_month <= 6'h31; // Jan

                5'h02: days_per_month <= (is_leap_year)? 6'h29:6'h28;

                5'h03: days_per_month <= 6'h31; // March

                5'h04: days_per_month <= 6'h30; // April

                5'h05: days_per_month <= 6'h31; // May

                5'h06: days_per_month <= 6'h30; // June

                5'h07: days_per_month <= 6'h31; // July

                5'h08: days_per_month <= 6'h31; // August

                5'h09: days_per_month <= 6'h30; // Sept

                5'h10: days_per_month <= 6'h31; // October

                5'h11: days_per_month <= 6'h30; // November

                5'h12: days_per_month <= 6'h31; // December

                default: days_per_month <= 6'h31; // Invalid month

                endcase

        end

        initial last_day_of_month = 1'b0;

        always @(posedge i_clk) // Clock 4

                last_day_of_month <= (r_day >= days_per_month);

        initial last_day_of_year = 1'b0;

        always @(posedge i_clk) // Clock 5

                last_day_of_year <= (last_day_of_month) && (r_mon == 5'h12);

        reg     year_divisible_by_four, century_year, four_century_year;

        always @(posedge i_clk) // Clock 1

                year_divisible_by_four<= ((~r_year[0])&&(r_year[4]==r_year[1]));

        always @(posedge i_clk) // Clock 1

                century_year <= (r_year[7:0] == 8'h00);

        always @(posedge i_clk) // Clock 1

                four_century_year <= ((~r_year[8])&&((r_year[12]==r_year[9])));

        always @(posedge i_clk) // Clock 2

                is_leap_year <= (year_divisible_by_four)&&((~century_year)

                        ||((century_year)&&(four_century_year)));

        // Adjust the day of month

        reg     [5:0]    next_day, fixd_day;

        always @(posedge i_clk)

                if (last_day_of_month)

                        next_day <= 6'h01;

                else if (r_day[3:0] != 4'h9)

                        next_day <= { r_day[5:4], (r_day[3:0]+4'h1) };

                else

                        next_day <= { (r_day[5:4]+2'h1), 4'h0 };

        always @(posedge i_clk)

                if ((r_day == 0)||(r_day > 6'h31)||(r_day[3:0] > 4'h9))

                        fixd_day <= 6'h01;

                else

                        fixd_day <= r_day;

        initial r_day = 6'h01;

        always @(posedge i_clk)

        begin // Depends upon 9 inputs

                if (i_ppd)

                        r_day <= next_day;

                else if (~o_wb_ack)

                        r_day <= fixd_day;

                if ((i_wb_stb)&&(i_wb_we)&&(~i_wb_data[7]))

                        r_day <= i_wb_data[5:0];

        end

        // Adjust the month of the year

        reg     [4:0]    next_mon, fixd_mon;

        always @(posedge i_clk)

                if (last_day_of_year)

                        next_mon <= 5'h01;

                else if ((last_day_of_month)&&(r_mon[3:0] != 4'h9))

                        next_mon <= { r_mon[4], (r_mon[3:0] + 4'h1) };

                else if (last_day_of_month)

                begin

                        next_mon[3:0] <= 4'h0;

                        next_mon[4] <= 1;

                end else

                        next_mon <= r_mon;

        always @(posedge i_clk)

                if ((r_mon == 0)||(r_mon > 5'h12)||(r_mon[3:0] > 4'h9))

                        fixd_mon <= 5'h01;

                else

                        fixd_mon <= r_mon;

        initial r_mon = 5'h01;

        always @(posedge i_clk)

        begin // Depeds upon 9 inputs

                if (i_ppd)

                        r_mon <= next_mon;

                else if (~o_wb_ack)

                        r_mon <= fixd_mon;

                if ((i_wb_stb)&&(i_wb_we)&&(~i_wb_data[15]))

                        r_mon <= i_wb_data[12:8];

        end

        // Adjust the year

        reg     [13:0]   next_year;

        reg     [2:0]    next_year_c;

        always @(posedge i_clk)

        begin // Takes 5 clocks to propagate

                next_year_c[0] <= (r_year[ 3: 0]>=4'h9);

                next_year_c[1] <= (r_year[ 7: 4]>4'h9)||((r_year[ 7: 4]==4'h9)&&(next_year_c[0]));

                next_year_c[2] <= (r_year[11: 8]>4'h9)||((r_year[11: 8]==4'h9)&&(next_year_c[1]));

                next_year[ 3: 0] <= (next_year_c[0])? 4'h0:(r_year[ 3: 0]+4'h1);

                next_year[ 7: 4] <= (next_year_c[1])? 4'h0:

                                        (next_year_c[0])?(r_year[ 7: 4]+4'h1)

                                        : (r_year[7:4]);

                next_year[11: 8] <= (next_year_c[2])? 4'h0:

                                        (next_year_c[1])?(r_year[11: 8]+4'h1)

                                        : (r_year[11: 8]);

                next_year[13:12] <= (next_year_c[2])?(r_year[13:12]+2'h1):r_year[13:12];

        end

        initial r_year = 14'h2000;

        always @(posedge i_clk)

        begin // 11 inputs

                // Deal with any out of bounds conditions

                if (r_year[3:0] > 4'h9)

                        r_year[3:0] <= 4'h0;

                if (r_year[7:4] > 4'h9)

                        r_year[7:4] <= 4'h0;

                if (r_year[11:8] > 4'h9)

                        r_year[11:8] <= 4'h0;

                if ((i_ppd)&&(last_day_of_year))

                        r_year <= next_year;

                if ((i_wb_stb)&&(i_wb_we)&&(~i_wb_data[31]))

                        r_year <= i_wb_data[29:16];

        end

        always @(posedge i_clk)

                o_wb_ack <= (i_wb_stb);

        assign  o_wb_stall = 1'b0;

        assign  o_wb_data = { 2'h0, r_year, 3'h0, r_mon, 2'h0, r_day };

endmodule