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

//

// Filename:    rtcgps.v

//              

// Project:     OpenArty, an entirely open SoC based upon the Arty platform

//

// Purpose:     Implement a real time clock, including alarm, count--down

//              timer, stopwatch, variable time frequency, and more.

//

//      This particular version has hooks for a GPS 1PPS, as well as a 

//      finely tracked clock speed output, to allow for fine clock precision

//      and good freewheeling even if/when GPS is lost.

//

//

// 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.

//

// 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  rtcgps(i_clk,

                // Wishbone interface

                i_wb_cyc, i_wb_stb, i_wb_we, i_wb_addr, i_wb_data,

                //      o_wb_ack, o_wb_stb, o_wb_data, // no reads here

                // Output registers

                o_data, // multiplexed based upon i_wb_addr

                // Output controls

                o_interrupt,

                // A once-per-day strobe on the last clock of the day

                o_ppd,

                // GPS interface

                i_gps_valid, i_gps_pps, i_gps_ckspeed,

                // Our personal timing, for debug purposes

                o_rtc_pps);

        parameter       DEFAULT_SPEED = 32'd2814750; //2af31e = 2^48 / 100e6 MHz

        //

        input                   i_clk;

        //

        input                   i_wb_cyc, i_wb_stb, i_wb_we;

        input           [1:0]    i_wb_addr;

        input           [31:0]   i_wb_data;

        // input                i_btn;

        output  reg     [31:0]   o_data;

        output  wire            o_interrupt, o_ppd;

        // GPS interface

        input                   i_gps_valid, i_gps_pps;

        input           [31:0]   i_gps_ckspeed;

        // Personal PPS

        output  wire            o_rtc_pps;

        reg     [21:0]   clock;

        reg     [31:0]   stopwatch, ckspeed;

        reg     [25:0]   timer;

        reg     ck_wr, tm_wr, sw_wr, al_wr, r_data_zero_byte;

        reg     [25:0]   r_data;

        always @(posedge i_clk)

        begin

                ck_wr <= ((i_wb_stb)&&(i_wb_addr==2'b00)&&(i_wb_we));

                tm_wr <= ((i_wb_stb)&&(i_wb_addr==2'b01)&&(i_wb_we));

                sw_wr <= ((i_wb_stb)&&(i_wb_addr==2'b10)&&(i_wb_we));

                al_wr <= ((i_wb_stb)&&(i_wb_addr==2'b11)&&(i_wb_we));

                r_data <= i_wb_data[25:0];

                r_data_zero_byte <= (i_wb_data[7:0] == 8'h00);

        end

        reg     [39:0]   ck_counter;

        reg             ck_carry, ck_sub_carry;

        always @(posedge i_clk)

                if ((i_gps_valid)&&(i_gps_pps))

                begin

                        ck_carry   <= 0;

                        // Start our counter 2 clocks into the future.

                        // Why?  Because if we hit the PPS, we'll be delayed

                        // one clock from true time.  This (hopefully) locks

                        // us back onto true time.  Further, if we end up

                        // off (i.e., go off before the GPS tick ...) then

                        // the GPS tick will put us back on track ... likewise

                        // we've got code following that should keep us from

                        // ever producing two PPS's per second.

                        ck_counter <= { 7'h00, ckspeed, 1'b0 };

                        ck_sub_carry <= ckspeed[31];

                end else begin

                        { ck_sub_carry, ck_counter[31:0] }

                                <= ck_counter[31:0] + ckspeed;

                        { ck_carry, ck_counter[39:32] }

                                <= ck_counter[39:32] + { 7'h0, ck_sub_carry };

                end

        reg             ck_pps;

        reg             ck_ppm, ck_pph, ck_ppd;

        reg     [7:0]    ck_sub;

        initial clock = 22'h00000000;

        always @(posedge i_clk)

                if ((i_gps_pps)&&(i_gps_valid)&&(ck_sub[7]))

                        ck_pps <= 1'b1;

                else if ((ck_carry)&&(ck_sub == 8'hff))

                        ck_pps <= 1'b1;

                else

                        ck_pps <= 1'b0;

        reg     [6:0]    next_clock_secs;

        always @(posedge i_clk)

        begin

                next_clock_secs[3:0] <= (clock[3:0] >= 4'h9) ? 4'h0 // clk 1

                                                : (clock[3:0] + 4'h1);

                next_clock_secs[6:4] <= (ck_ppm) ? 3'h0 // clk 2

                                        : (clock[3:0] >= 4'h9)

                                                ? (clock[6:4] + 3'h1)

                                                : clock[6:4];

        end

        reg     [6:0]    next_clock_mins;

        always @(posedge i_clk)

        begin

                next_clock_mins[3:0] <= (clock[11:8] >= 4'h9) ? 4'h0

                                                : (clock[11:8] + 4'h1);

                next_clock_mins[6:4] <= (ck_pph) ? 3'h0

                                        : (clock[11:8] >= 4'h9)

                                                ? (clock[14:12] + 3'h1)

                                                : clock[14:12];

        end

        reg     [5:0]    next_clock_hrs;

        always @(posedge i_clk)

        begin

                next_clock_hrs[3:0] <= (clock[19:16] >= 4'h9) ? 4'h0

                                                : (clock[19:16] + 4'h1);

                next_clock_hrs[5:4] <= (ck_ppd) ? 2'h0

                                        : (clock[19:16] >= 4'h9)

                                                ? (clock[21:20] + 2'h1)

                                                : (clock[21:20]);

        end

        reg     [4:0] ck_pending;

        assign  o_rtc_pps = ck_pps;

        always @(posedge i_clk)

        begin

                if ((i_gps_valid)&&(i_gps_pps))

                        ck_sub <= 0;

                else if (ck_carry)

                        ck_sub <= ck_sub + 1;

                if ((ck_pps)&&(~ck_pending[4])) // advance the seconds

                        clock[6:0] <= next_clock_secs;

                clock[7] <= 1'b0;

                ck_ppm <= (clock[6:0] == 7'h59);

                if ((ck_pps)&&(ck_ppm)&&(~ck_pending[4])) // advance the minutes

                        clock[14:8] <= next_clock_mins;

                clock[15] <= 1'b0;

                ck_pph <= (clock[14:8] == 7'h59)&&(ck_ppm);

                if ((ck_pps)&&(ck_pph)&&(~ck_pending[4])) // advance the hours

                        clock[21:16] <= next_clock_hrs;

                ck_ppd <= (clock[21:16] == 6'h23)&&(ck_pph);

                clock[ 7] <= 1'b0;

                clock[15] <= 1'b0;

                if (ck_wr)

                begin

                        if (~r_data[7])

                                clock[6:0] <= i_wb_data[6:0];

                        if (~r_data[15])

                                clock[14:8] <= i_wb_data[14:8];

                        if (~r_data[22])

                                clock[21:16] <= i_wb_data[21:16];

                        if ((~i_gps_valid)&&(r_data_zero_byte))

                                ck_sub <= 8'h00;

                        ck_pending <= 5'h1f;

                end else

                        ck_pending <= { ck_pending[3:0], 1'b0 };

        end

        reg     [21:0]   ck_last_clock;

        always @(posedge i_clk)

                ck_last_clock <= clock[21:0];

        // 

        reg     [23:0]   next_timer;

        reg             ztimer;

        reg     [4:0]    tmr_carry;

        always @(posedge i_clk)

        begin

                tmr_carry[0] <= (timer[ 3: 0]== 4'h0);

                tmr_carry[1] <= (timer[ 6: 4]== 3'h0)&&(tmr_carry[0]);

                tmr_carry[2] <= (timer[11: 8]== 4'h0)&&(tmr_carry[1]);

                tmr_carry[3] <= (timer[14:12]== 3'h0)&&(tmr_carry[2]);

                tmr_carry[4] <= (timer[19:16]== 4'h0)&&(tmr_carry[3]);

                ztimer <= (timer[23:0]== 24'h0);

                // Keep unused bits at zero

                next_timer <= 24'h00;

                // Seconds

                next_timer[ 3: 0] <= (tmr_carry[0])? 4'h9: (timer[ 3: 0]-4'h1);

                next_timer[ 6: 4] <= (tmr_carry[1])? 3'h5: (timer[ 6: 4]-3'h1);

                // Minutes

                next_timer[11: 8] <= (tmr_carry[2])? 4'h9: (timer[11: 8]-4'h1);

                next_timer[14:12] <= (tmr_carry[3])? 3'h5: (timer[14:12]-3'h1);

                // Hours

                next_timer[19:16] <= (tmr_carry[4])? 4'h9: (timer[19:16]-4'h1);

                next_timer[23:20] <= (timer[23:20]-4'h1);

        end

        reg     new_timer, new_timer_set, new_timer_last, tm_pending_start;

        reg     [23:0]   new_timer_val;

        reg     tm_pps, tm_ppm, tm_int;

        wire    tm_stopped, tm_running, tm_alarm;

        assign  tm_stopped = ~timer[24];

        assign  tm_running =  timer[24];

        assign  tm_alarm   =  timer[25];

        reg     [23:0]           tm_start;

        reg     [7:0]            tm_sub;

        initial tm_start = 24'h00;

        initial timer    = 26'h00;

        initial tm_int   = 1'b0;

        initial tm_pps   = 1'b0;

        initial tm_pending_start = 1'b0;

        always @(posedge i_clk)

        begin

                if (ck_carry)

                begin

                        tm_sub <= tm_sub + 1;

                        tm_pps <= (tm_sub == 8'hff);

                end else

                        tm_pps <= 1'b0;

                if (new_timer_set) // Conclude a write

                        timer[23:0] <= new_timer_val;

                else if ((~tm_alarm)&&(tm_running)&&(tm_pps))

                begin // Otherwise, if we are running ...

                        timer[25] <= 1'b0; // Clear any alarm

                        if (ztimer) // unless we've hit zero

                                timer[25] <= 1'b1;

                        else if (~new_timer)

                                timer[23:0] <= next_timer;

                end

                tm_int <= (tm_running)&&(tm_pps)&&(~tm_alarm)&&(ztimer);

                if (tm_alarm) // Stop the timer on an alarm

                        timer[24] <= 1'b0;

                new_timer <= 1'b0;

                tm_pending_start <= 1'b0;

                if ((tm_wr)&&(tm_running)) // Writes while running

                        // Only allow the timer to stop, nothing more

                        timer[24] <= r_data[24];

                else if ((tm_wr)&&(tm_stopped)) // Writes while off

                begin

                        // We're going to pipeline this change by a couple

                        // of clocks, to get it right

                        new_timer <= 1'b1;

                        new_timer_val <= r_data[23:0];

                        tm_pending_start <= r_data[24];

                        // Still ... any write clears the alarm

                        timer[25] <= 1'b0;

                end

                new_timer_set  <= (new_timer)&&(new_timer_val != 24'h000);

                new_timer_last <= (new_timer)&&(new_timer_val == 24'h000);

                if (new_timer_last)

                begin

                        new_timer_val <= tm_start;

                        tm_sub <= 8'h00;

                        new_timer_set <= 1'b1;

                        tm_pending_start <= 1'b1;

                end else if (new_timer_set)

                begin

                        tm_start <= new_timer_val;

                        tm_sub <= 8'h00;

                        tm_pending_start <= 1'b1;

                        timer[24] <= 1'b1;

                end

        end

        //

        // Stopwatch functionality

        //

        // Setting bit '0' starts the stop watch, clearing it stops it.

        // Writing to the register with bit '1' high will clear the stopwatch,

        // and return it to zero provided that the stopwatch is stopped either

        // before or after the write.  Hence, writing a '2' to the device

        // will always stop and clear it, whereas writing a '3' to the device

        // will only clear it if it was already stopped.

        reg     [6:0]    next_sw_secs;

        always @(posedge i_clk)

        begin

                next_sw_secs[3:0] <= (stopwatch[11:8] >= 4'h9) ? 4'h0

                                                : (stopwatch[11:8] + 4'h1);

                next_sw_secs[6:4] <= (stopwatch[14:8] == 7'h59) ? 3'h0

                                        : (stopwatch[11:8] == 4'h9)

                                                ? (stopwatch[14:12]+3'h1)

                                                : stopwatch[14:12];

        end

        reg     [6:0]    next_sw_mins;

        always @(posedge i_clk)

        begin

                next_sw_mins[3:0] <= (stopwatch[19:16] >= 4'h9) ? 4'h0

                                                : (stopwatch[19:16] + 4'h1);

                next_sw_mins[6:4] <= (stopwatch[22:16] == 7'h59) ? 3'h0

                                        : (stopwatch[19:16]==4'h9)

                                                ? (stopwatch[22:20]+3'h1)

                                                : stopwatch[22:20];

        end

        reg     [5:0]    next_sw_hrs;

        always @(posedge i_clk)

        begin

                next_sw_hrs[3:0] <= (stopwatch[27:24] >= 4'h9) ? 4'h0

                                                : (stopwatch[27:24] + 4'h1);

                next_sw_hrs[5:4] <= (stopwatch[29:24] >= 6'h23) ? 2'h0

                                        : (stopwatch[27:24]==4'h9)

                                                ? (stopwatch[29:28]+2'h1)

                                                : stopwatch[29:28];

        end

        reg             sw_pps, sw_ppm, sw_pph;

        reg     [7:0]    sw_sub;

        wire    sw_running;

        assign  sw_running = stopwatch[0];

        initial stopwatch = 32'h00000;

        always @(posedge i_clk)

        begin

                sw_pps <= 1'b0;

                if ((sw_running)&&(ck_carry))

                begin

                        sw_sub <= sw_sub + 1;

                        sw_pps <= (sw_sub == 8'hff);

                end

                stopwatch[7:1] <= sw_sub[7:1];

                if (sw_pps) // Second hand

                        stopwatch[14:8] <= next_sw_secs;

                sw_ppm <= (stopwatch[14:8] == 7'h59);

                if ((sw_pps)&&(sw_ppm)) // Minutes

                        stopwatch[22:16] <= next_sw_mins;

                sw_pph <= (stopwatch[23:16] == 8'h59)&&(sw_ppm);

                if ((sw_pps)&&(sw_pph)) // And hours

                        stopwatch[29:24] <= next_sw_hrs;

                if (sw_wr)

                begin

                        stopwatch[0] <= r_data[0];

                        if((r_data[1])&&((~stopwatch[0])||(~r_data[0])))

                        begin

                                stopwatch[31:1] <= 31'h00;

                                sw_sub <= 8'h00;

                                sw_pps <= 1'b0;

                                sw_ppm <= 1'b0;

                                sw_pph <= 1'b0;

                        end

                end

        end

        //

        // The alarm code

        //

        // Set the alarm register to the time you wish the board to "alarm".

        // The "alarm" will take place once per day at that time.  At that

        // time, the RTC code will generate a clock interrupt, and the CPU/host

        // can come and see that the alarm tripped.

        //

        // 

        reg     [21:0]           alarm_time;

        reg                     al_int,         // The alarm interrupt line

                                al_enabled,     // Whether the alarm is enabled

                                al_tripped;     // Whether the alarm has tripped

        initial al_enabled= 1'b0;

        initial al_tripped= 1'b0;

        always @(posedge i_clk)

        begin

                if (al_wr)

                begin

                        // Only adjust the alarm hours if the requested hours

                        // are valid.  This allows writes to the register,

                        // without a prior read, to leave these configuration

                        // bits alone.

                        if (r_data[21:20] != 2'h3)

                                alarm_time[21:16] <= i_wb_data[21:16];

                        // Here's the same thing for the minutes: only adjust

                        // the alarm minutes if the new bits are not all 1's. 

                        if (~r_data[15])

                                alarm_time[15:8] <= i_wb_data[15:8];

                        // Here's the same thing for the seconds: only adjust

                        // the alarm seconds if the new bits are not all 1's. 

                        if (~r_data[7])

                                alarm_time[7:0] <= i_wb_data[7:0];

                        al_enabled <= i_wb_data[24];

                        // Reset the alarm if a '1' is written to the tripped

                        // register, or if the alarm is disabled.

                        if ((r_data[25])||(~r_data[24]))

                                al_tripped <= 1'b0;

                end

                al_int <= ((ck_last_clock != alarm_time)

                                &&(clock[21:0] == alarm_time)&&(al_enabled));

                if (al_int)

                        al_tripped <= 1'b1;

        end

        //

        // The ckspeed register is equal to 2^48 divded by the number of

        // clock ticks you expect per second.  Adjust high for a slower

        // clock, lower for a faster clock.  In this fashion, a single

        // real time clock RTL file can handle tracking the clock in any

        // device.  Further, because this is only the lower 32 bits of a 

        // 48 bit counter per seconds, the clock jitter is kept below

        // 1 part in 65 thousand.

        //

        initial ckspeed = DEFAULT_SPEED;

        // In the case of verilator, comment the above and uncomment the line

        // below.  The clock constant below is "close" to simulation time,

        // meaning that my verilator simulation is running about 300x slower

        // than board time.

        // initial      ckspeed = 32'd786432000;

        always @(posedge i_clk)

                if (i_gps_valid)

                        ckspeed <= i_gps_ckspeed;

        assign  o_interrupt = tm_int || al_int;

        // A once-per day strobe, on the last second of the day so that the

        // the next clock is the first clock of the day.  This is useful for

        // connecting this module to a year/month/date date/calendar module.

        assign  o_ppd = (ck_ppd)&&(ck_pps);

        always @(posedge i_clk)

                case(i_wb_addr)

                2'b00: o_data <= { ~i_gps_valid, 7'h0, 2'b00, clock[21:0] };

                2'b01: o_data <= { 6'h00, timer };

                2'b10: o_data <= stopwatch;

                2'b11: o_data <= { 6'h00, al_tripped, al_enabled, 2'b00, alarm_time };

                endcase

endmodule