///////////////////////////////////////////////////////////////////////////
//
// Filename: 	rtclight.v
//		
// Project:	A Wishbone Controlled Real--time Clock Core
//
// Purpose:	Implement a real time clock, including alarm, count--down
//		timer, stopwatch, variable time frequency, and more.
//
//	This is a light-weight version of the RTC found in this directory.
//	Unlike the full RTC, this version does not support time hacks, seven
//	segment display outputs, or LED's.  It is an RTC for an internal core
//	only.  (That's how I was using it on one of my projects anyway ...)
//
//
// 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
//
//// SPDX-License-Identifier: GPL-3.0-or-later 
///////////////////////////////////////////////////////////////////////////
module	rtclight(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
		// // Button inputs
		// i_btn,
		// 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);
	parameter	DEFAULT_SPEED = 32'd2814750;	// 100 Mhz
	input	i_clk;
	input	i_wb_cyc, i_wb_stb, i_wb_we;
	input	[2:0]	i_wb_addr;
	input	[31:0]	i_wb_data;
	// input		i_btn;
	output	reg	[31:0]	o_data;
	output	wire		o_interrupt, o_ppd;

	reg	[21:0]	clock;
	reg	[31:0]	stopwatch, ckspeed;
	reg	[25:0]	timer;
	
	wire	ck_sel, tm_sel, sw_sel, sp_sel, al_sel;
	assign	ck_sel = ((i_wb_cyc)&&(i_wb_stb)&&(i_wb_addr[2:0]==3'b000));
	assign	tm_sel = ((i_wb_cyc)&&(i_wb_stb)&&(i_wb_addr[2:0]==3'b001));
	assign	sw_sel = ((i_wb_cyc)&&(i_wb_stb)&&(i_wb_addr[2:0]==3'b010));
	assign	al_sel = ((i_wb_cyc)&&(i_wb_stb)&&(i_wb_addr[2:0]==3'b011));
	assign	sp_sel = ((i_wb_cyc)&&(i_wb_stb)&&(i_wb_addr[2:0]==3'b100));

	reg		ck_carry;
	reg	[39:0]	ck_counter;
	initial		ck_carry = 1'b0;
	initial		ck_counter = 40'h00;
	always @(posedge i_clk)
		{ ck_carry, ck_counter } <= ck_counter + { 8'h00, ckspeed };

	wire		ck_pps;
	reg		ck_prepps, ck_ppm, ck_pph, ck_ppd;
	reg	[7:0]	ck_sub;
	initial	clock = 22'h00000;
	assign	ck_pps = (ck_carry)&&(ck_prepps);
	always @(posedge i_clk)
	begin
		if (ck_carry)
			ck_sub <= ck_sub + 8'h1;
		ck_prepps <= (ck_sub == 8'hff);

		if (ck_pps)
		begin // advance the seconds
			if (clock[3:0] >= 4'h9)
				clock[3:0] <= 4'h0;
			else
				clock[3:0] <= clock[3:0] + 4'h1;
			if (clock[7:0] >= 8'h59)
				clock[7:4] <= 4'h0;
			else if (clock[3:0] >= 4'h9)
				clock[7:4] <= clock[7:4] + 4'h1;
		end
		ck_ppm <= (clock[7:0] == 8'h59);

		if ((ck_pps)&&(ck_ppm))
		begin // advance the minutes
			if (clock[11:8] >= 4'h9)
				clock[11:8] <= 4'h0;
			else
				clock[11:8] <= clock[11:8] + 4'h1;
			if (clock[15:8] >= 8'h59)
				clock[15:12] <= 4'h0;
			else if (clock[11:8] >= 4'h9)
				clock[15:12] <= clock[15:12] + 4'h1;
		end
		ck_pph <= (clock[15:0] == 16'h5959);

		if ((ck_pps)&&(ck_pph))
		begin // advance the hours
			if (clock[21:16] >= 6'h23)
			begin
				clock[19:16] <= 4'h0;
				clock[21:20] <= 2'h0;
			end else if (clock[19:16] >= 4'h9)
			begin
				clock[19:16] <= 4'h0;
				clock[21:20] <= clock[21:20] + 2'h1;
			end else begin
				clock[19:16] <= clock[19:16] + 4'h1;
			end
		end
		ck_ppd <= (clock[21:0] == 22'h235959);


		if ((ck_sel)&&(i_wb_we))
		begin
			if (8'hff != i_wb_data[7:0])
			begin
				clock[7:0] <= i_wb_data[7:0];
				ck_ppm <= (i_wb_data[7:0] == 8'h59);
			end
			if (8'hff != i_wb_data[15:8])
			begin
				clock[15:8] <= i_wb_data[15:8];
				ck_pph <= (i_wb_data[15:8] == 8'h59);
			end
			if (6'h3f != i_wb_data[21:16])
				clock[21:16] <= i_wb_data[21:16];
			if (8'h00 == i_wb_data[7:0])
				ck_sub <= 8'h00;
		end
	end

	// Clock updates take several clocks, so let's make sure we
	// are only looking at a valid clock value before testing it.
	reg	[21:0]		ck_last_clock;
	always @(posedge i_clk)
		ck_last_clock <= clock[21:0];
		

	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;
	always @(posedge i_clk)
	begin
		if (ck_carry)
		begin
			tm_sub <= tm_sub + 8'h1;
			tm_pps <= (tm_sub == 8'hff);
		end else
			tm_pps <= 1'b0;
		
		if ((~tm_alarm)&&(tm_running)&&(tm_pps))
		begin // If we are running ...
			timer[25] <= 1'b0;
			if (timer[23:0] == 24'h00)
				timer[25] <= 1'b1;
			else if (timer[3:0] != 4'h0)
				timer[3:0] <= timer[3:0]-4'h1;
			else begin // last digit is a zero
				timer[3:0] <= 4'h9;
				if (timer[7:4] != 4'h0)
					timer[7:4] <= timer[7:4]-4'h1;
				else begin // last two digits are zero
					timer[7:4] <= 4'h5;
					if (timer[11:8] != 4'h0)
						timer[11:8] <= timer[11:8]-4'h1;
					else begin // last three digits are zero
						timer[11:8] <= 4'h9;
						if (timer[15:12] != 4'h0)
							timer[15:12] <= timer[15:12]-4'h1;
						else begin
							timer[15:12] <= 4'h5;
							if (timer[19:16] != 4'h0)
								timer[19:16] <= timer[19:16]-4'h1;
							else begin
							//
								timer[19:16] <= 4'h9;
								timer[23:20] <= timer[23:20]-4'h1;
							end
						end
					end
				end
			end
		end

		if((~tm_alarm)&&(tm_running))
		begin
			timer[25] <= (timer[23:0] == 24'h00);
			tm_int <= (timer[23:0] == 24'h00);
		end else tm_int <= 1'b0;
		if (tm_alarm)
			timer[24] <= 1'b0;

		if ((tm_sel)&&(i_wb_we)&&(tm_running)) // Writes while running
			// Only allowed to stop the timer, nothing more
			timer[24] <= i_wb_data[24];
		else if ((tm_sel)&&(i_wb_we)&&(tm_stopped)) // Writes while off
		begin
			timer[24] <= i_wb_data[24];
			if ((timer[24])||(i_wb_data[24]))
				timer[25] <= 1'b0;
			if (i_wb_data[23:0] != 24'h0000)
			begin
				timer[23:0] <= i_wb_data[23:0];
				tm_start <= i_wb_data[23:0];
				tm_sub <= 8'h00;
			end else if (timer[23:0] == 24'h00)
			begin // Resetting timer to last valid timer start val
				timer[23:0] <= tm_start;
				tm_sub <= 8'h00;
			end
			// Any write clears the alarm
			timer[25] <= 1'b0;
		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		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)
		begin
			if (ck_carry)
			begin
				sw_sub <= sw_sub + 8'h1;
				sw_pps <= (sw_sub == 8'hff);
			end
		end

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

		if (sw_pps)
		begin // Second hand
			if (stopwatch[11:8] >= 4'h9)
				stopwatch[11:8] <= 4'h0;
			else
				stopwatch[11:8] <= stopwatch[11:8] + 4'h1;

			if (stopwatch[15:8] >= 8'h59)
				stopwatch[15:12] <= 4'h0;
			else if (stopwatch[11:8] >= 4'h9)
				stopwatch[15:12] <= stopwatch[15:12] + 4'h1;
			sw_ppm <= (stopwatch[15:8] == 8'h59);
		end else sw_ppm <= 1'b0;

		if (sw_ppm)
		begin // Minutes
			if (stopwatch[19:16] >= 4'h9)
				stopwatch[19:16] <= 4'h0;
			else
				stopwatch[19:16] <= stopwatch[19:16]+4'h1;

			if (stopwatch[23:16] >= 8'h59)
				stopwatch[23:20] <= 4'h0;
			else if (stopwatch[19:16] >= 4'h9)
				stopwatch[23:20] <= stopwatch[23:20]+4'h1;
			sw_pph <= (stopwatch[23:16] == 8'h59);
		end else sw_pph <= 1'b0;

		if (sw_pph)
		begin // And hours
			if (stopwatch[27:24] >= 4'h9)
				stopwatch[27:24] <= 4'h0;
			else
				stopwatch[27:24] <= stopwatch[27:24]+4'h1;

			if((stopwatch[27:24] >= 4'h9)&&(stopwatch[31:28] < 4'hf))
				stopwatch[31:28] <= stopwatch[27:24]+4'h1;
		end

		if ((sw_sel)&&(i_wb_we))
		begin
			stopwatch[0] <= i_wb_data[0];
			if((i_wb_data[1])&&((~stopwatch[0])||(~i_wb_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_sel)&&(i_wb_we))
		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 (i_wb_data[21:16] != 6'h3f)
				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 (i_wb_data[15:8] != 8'hff)
				alarm_time[15:8] <= i_wb_data[15:8];
			// Here's the same thing for the seconds: only adjust
			// the alarm minutes if the new bits are not all 1's. 
			if (i_wb_data[7:0] != 8'hff)
				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 ((i_wb_data[25])||(~i_wb_data[24]))
				al_tripped <= 1'b0;
		end

		al_int <= 1'b0;
		if ((ck_last_clock != alarm_time)&&(clock[21:0] == alarm_time)
			&&(al_enabled))
		begin
			al_tripped <= 1'b1;
			al_int <= 1'b1;
		end
	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; // 2af31e = 2^48 / 100e6 MHz
	// 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 ((sp_sel)&&(i_wb_we))
			ckspeed <= i_wb_data;

	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[2:0])
		3'b000: o_data <= { 10'h0, ck_last_clock };
		3'b001: o_data <= { 6'h00, timer };
		3'b010: o_data <= stopwatch;
		3'b011: o_data <= { 6'h00, al_tripped, al_enabled, 2'b00, alarm_time };
		3'b100: o_data <= ckspeed;
		default: o_data <= 32'h000;
		endcase

endmodule