`timescale 1ns / 1ps
module SimROM(
	input [15:0] address,
	inout [7:0] data,
	input clk,
	input wr, rd);

	reg rdlatch = 0;
	reg [7:0] odata;

	reg [7:0] rom [32767:0];
	initial $readmemh("rom.hex", rom);

	wire decode = address[15:13] == 0;
	always @(posedge clk) begin
		rdlatch <= rd && decode;
		odata <= rom[address[10:0]];
	end
	assign data = rdlatch ? odata : 8'bzzzzzzzz;
endmodule

module BootstrapROM(
	input [15:0] address,
	inout [7:0] data,
	input clk,
	input wr, rd);

	reg rdlatch = 0;
	reg [7:0] addrlatch = 0;
	reg romno = 0, romnotmp = 0;
	reg [7:0] brom0 [255:0];
	reg [7:0] brom1 [255:0];
	
	initial $readmemh("fpgaboot.hex", brom0);
	initial $readmemh("gbboot.hex", brom1);
	
`ifdef isim
	initial romno <= 1;
`endif

	wire decode = address[15:8] == 0;
	wire [7:0] odata = (romno == 0) ? brom0[addrlatch] : brom1[addrlatch];
	always @(posedge clk) begin
		rdlatch <= rd && decode;
		addrlatch <= address[7:0];
		if (wr && decode) romnotmp <= data[0];
		if (rd && address == 16'h0000) romno <= romnotmp;	/* Latch when the program restarts. */
	end
	assign data = rdlatch ? odata : 8'bzzzzzzzz;
endmodule

module MiniRAM(
	input [15:0] address,
	inout [7:0] data,
	input clk,
	input wr, rd);
	
	reg [7:0] ram [127:0];
	
	wire decode = (address >= 16'hFF80) && (address <= 16'hFFFE);
	reg rdlatch = 0;
	reg [7:0] odata;
	assign data = rdlatch ? odata : 8'bzzzzzzzz;
	
	always @(posedge clk)
	begin
		rdlatch <= rd && decode;
		if (decode)		// This has to go this way. The only way XST knows how to do
		begin			// block ram is chip select, write enable, and always
			if (wr)		// reading. "else if rd" does not cut it ...
				ram[address[6:0]] <= data;
			odata <= ram[address[6:0]];
		end
	end
endmodule

module CellularRAM(
	input clk,
	input [15:0] address,
	inout [7:0] data,
	input wr, rd,
	output wire cr_nADV, cr_nCE, cr_nOE, cr_nWE, cr_CRE, cr_nLB, cr_nUB, cr_CLK,
	output wire [22:0] cr_A,
	inout [15:0] cr_DQ);
	
	parameter ADDR_PROGADDRH = 16'hFF60;
	parameter ADDR_PROGADDRM = 16'hFF61;
	parameter ADDR_PROGADDRL = 16'hFF62;
	parameter ADDR_PROGDATA = 16'hFF63;
	parameter ADDR_MBC = 16'hFF64;
	
	reg rdlatch = 0, wrlatch = 0;
	reg [15:0] addrlatch = 0;
	reg [7:0] datalatch = 0;
	
	reg [7:0] progaddrh, progaddrm, progaddrl;
	
	reg [22:0] progaddr;
	
	reg [7:0] mbc_emul = 8'b00000101;	// High bit is whether we're poking flash
						// low 7 bits are the MBC that we are emulating
	
	assign cr_nADV = 0;	/* Addresses are always valid! :D */
	assign cr_nCE = 0;	/* The chip is enabled */
	assign cr_nLB = 0;	/* Lower byte is enabled */
	assign cr_nUB = 0;	/* Upper byte is enabled */
	assign cr_CRE = 0;	/* Data writes, not config */
	assign cr_CLK = 0;	/* Clock? I think not! */
	
	wire decode = (addrlatch[15:14] == 2'b00) /* extrom */ || (addrlatch[15:13] == 3'b101) /* extram */ || (addrlatch == ADDR_PROGDATA);
	
	reg [3:0] rambank = 0;
	reg [8:0] rombank = 1;
	
	assign cr_nOE = decode ? ~rdlatch : 1;
	assign cr_nWE = (decode && ((addrlatch == ADDR_PROGDATA) || (mbc_emul[6:0] == 0))) ? ~wrlatch : 1;
	
	assign cr_DQ = (~cr_nOE) ? 16'bzzzzzzzzzzzzzzzz : {8'b0, datalatch};
	assign cr_A = (addrlatch[15:14] == 2'b00) ? /* extrom, home bank */ {9'b0,addrlatch[13:0]} :
			(addrlatch[15:14] == 2'b01) ? /* extrom, paged bank */ {rombank, addrlatch[13:0]} :
			(addrlatch[15:13] == 3'b101) ? /* extram */ {1'b1, 5'b0, rambank, addrlatch[12:0]} :
			(addrlatch == ADDR_PROGDATA) ? progaddr :
			23'b0;
	
	always @(posedge clk) begin
		case (address)
		ADDR_PROGADDRH: if (wr) progaddrh <= data;
		ADDR_PROGADDRM: if (wr) progaddrm <= data;
		ADDR_PROGADDRL: if (wr) progaddrl <= data;
		ADDR_PROGDATA:	if (rd || wr) begin
					progaddr <= {progaddrh[6:0], progaddrm[7:0], progaddrl[7:0]};
					{progaddrh[6:0], progaddrm[7:0], progaddrl[7:0]} <= {progaddrh[6:0], progaddrm[7:0], progaddrl[7:0]} + 23'b1;
				end
		ADDR_MBC:	begin
					mbc_emul <= data;
					rambank <= 0;
					rombank <= 1;
				end
		endcase
		
		if (mbc_emul[6:0] == 5) begin
			if ((address[15:12] == 4'h2) && wr)
				rombank <= {rombank[8], data};
			else if ((address[15:12] == 4'h3) && wr)
				rombank <= {data[0], rombank[7:0]};
			else if ((address[15:12] == 4'h4) && wr)
				rambank <= data[3:0];
		end
		
		rdlatch <= rd;
		wrlatch <= wr;
		addrlatch <= address;
		datalatch <= data;
	end
	
	assign data = (rdlatch && decode) ?
				(addrlatch == ADDR_PROGADDRH) ? progaddrh :
				(addrlatch == ADDR_PROGADDRM) ? progaddrm :
				(addrlatch == ADDR_PROGADDRL) ? progaddrl :
				cr_DQ
			: 8'bzzzzzzzz;
endmodule

module InternalRAM(
	input [15:0] address,
	inout [7:0] data,
	input clk,
	input wr, rd);
	
	// synthesis attribute ram_style of ram is block
	reg [7:0] ram [8191:0];
	
	wire decode = (address >= 16'hC000) && (address <= 16'hFDFF);	/* This includes echo RAM. */
	reg [7:0] odata;
	reg rdlatch = 0;
	assign data = rdlatch ? odata : 8'bzzzzzzzz;
	
	always @(posedge clk)
	begin
		rdlatch <= rd && decode;
		if (decode)		// This has to go this way. The only way XST knows how to do
		begin			// block ram is chip select, write enable, and always
			if (wr)		// reading. "else if rd" does not cut it ...
				ram[address[12:0]] <= data;
			odata <= ram[address[12:0]];
		end
	end
endmodule

module Switches(
	input [15:0] address,
	inout [7:0] data,
	input clk,
	input wr, rd,
	input [7:0] switches,
	output reg [7:0] ledout = 0);
	
	wire decode = address == 16'hFF51;
	reg [7:0] odata;
	reg rdlatch = 0;
	assign data = rdlatch ? odata : 8'bzzzzzzzz;
	
	always @(posedge clk)
	begin
		rdlatch <= rd && decode;
		if (decode && rd)
			odata <= switches;
		else if (decode && wr)
			ledout <= data;
	end
endmodule

`ifdef isim
module Dumpable(input [2:0] r, g, input [1:0] b, input hs, vs, vgaclk);
endmodule
`endif

module CoreTop(
`ifdef isim
	output reg vgaclk = 0,
	output reg clk = 0,
`else
	input xtal,
	input [7:0] switches,
	input [3:0] buttons,
	output wire [7:0] leds,
	output serio,
	input serin,
	output wire [3:0] digits,
	output wire [7:0] seven,
	output wire cr_nADV, cr_nCE, cr_nOE, cr_nWE, cr_CRE, cr_nLB, cr_nUB, cr_CLK,
	output wire [22:0] cr_A,
	inout [15:0] cr_DQ,
`endif
	output wire hs, vs,
	output wire [2:0] r, g,
	output wire [1:0] b,
	output wire soundl, soundr);

`ifdef isim
	always #62 clk <= ~clk;
	always #100 vgaclk <= ~vgaclk;
	
	Dumpable dump(r,g,b,hs,vs,vgaclk);
	
	wire [7:0] leds;
	wire serio;
	wire serin = 1;
	wire [3:0] digits;
	wire [7:0] seven;
	wire [7:0] switches = 8'b0;
	wire [3:0] buttons = 4'b0;
`else	
	wire xtalb, clk, vgaclk;
	IBUFG iclkbuf(.O(xtalb), .I(xtal));
	CPUDCM dcm (.CLKIN_IN(xtalb), .CLKFX_OUT(clk));
	pixDCM pixdcm (.CLKIN_IN(xtalb), .CLKFX_OUT(vgaclk));
`endif

	wire [15:0] addr [1:0];
	wire [7:0] data [1:0];
	wire wr [1:0], rd [1:0];
	
	wire irq, tmrirq, lcdcirq, vblankirq;
	wire [7:0] jaddr;
	wire [1:0] state;
	
	GBZ80Core core(
		.clk(clk),
		.bus0address(addr[0]),
		.bus0data(data[0]),
		.bus0wr(wr[0]),
		.bus0rd(rd[0]),
		.bus1address(addr[1]),
		.bus1data(data[1]),
		.bus1wr(wr[1]),
		.bus1rd(rd[1]),
		.irq(irq),
		.jaddr(jaddr),
		.state(state));
	
	BootstrapROM brom(
		.address(addr[1]),
		.data(data[1]),
		.clk(clk),
		.wr(wr[1]),
		.rd(rd[1]));
	
`ifdef isim
	SimROM rom(
		.address(addr[0]),
		.data(data[0]),
		.clk(clk),
		.wr(wr[0]),
		.rd(rd[0]));
`else
	CellularRAM cellram(
		.address(addr[0]),
		.data(data[0]),
		.clk(clk),
		.wr(wr[0]),
		.rd(rd[0]),
		.cr_nADV(cr_nADV),
		.cr_nCE(cr_nCE),
		.cr_nOE(cr_nOE),
		.cr_nWE(cr_nWE),
		.cr_CRE(cr_CRE),
		.cr_nLB(cr_nLB),
		.cr_nUB(cr_nUB),
		.cr_CLK(cr_CLK),
		.cr_A(cr_A),
		.cr_DQ(cr_DQ));
`endif
	
	wire lcdhs, lcdvs, lcdclk;
	wire [2:0] lcdr, lcdg;
	wire [1:0] lcdb;
	
	LCDC lcdc(
		.clk(clk),
		.addr(addr[0]),
		.data(data[0]),
		.wr(wr[0]),
		.rd(rd[0]),
		.lcdcirq(lcdcirq),
		.vblankirq(vblankirq),
		.lcdclk(lcdclk),
		.lcdhs(lcdhs),
		.lcdvs(lcdvs),
		.lcdr(lcdr),
		.lcdg(lcdg),
		.lcdb(lcdb));
	
	Framebuffer fb(
		.lcdclk(lcdclk),
		.lcdhs(lcdhs),
		.lcdvs(lcdvs),
		.lcdr(lcdr),
		.lcdg(lcdg),
		.lcdb(lcdb),
		.vgaclk(vgaclk),
		.vgahs(hs),
		.vgavs(vs),
		.vgar(r),
		.vgag(g),
		.vgab(b));

	Switches sw(
		.clk(clk),
		.address(addr[0]),
		.data(data[0]),
		.wr(wr[0]),
		.rd(rd[0]),
		.ledout(leds),
		.switches(switches)
		);

	AddrMon amon(
		.clk(clk), 
		.addr(addr[0]),
		.digit(digits), 
		.out(seven),
		.freeze(buttons[0]),
		.periods(
			(state == 2'b00) ? 4'b0010 :
			(state == 2'b01) ? 4'b0001 :
			(state == 2'b10) ? 4'b1000 :
			                   4'b0100) );
	 
	UART nouart (	/* no u */
		.clk(clk),
		.addr(addr[0]),
		.data(data[0]),
		.wr(wr[0]),
		.rd(rd[0]),
		.serial(serio),
		.serialrx(serin)
		);

	InternalRAM ram(
		.clk(clk),
		.address(addr[0]),
		.data(data[0]),
		.wr(wr[0]),
		.rd(rd[0])
		);
	
	MiniRAM mram(
		.clk(clk),
		.address(addr[1]),
		.data(data[1]),
		.wr(wr[1]),
		.rd(rd[1])
		);

	Timer tmr(
		.clk(clk),
		.addr(addr[0]),
		.data(data[0]),
		.wr(wr[0]),
		.rd(rd[0]),
		.irq(tmrirq)
		);
	
	Interrupt intr(
		.clk(clk),
		.addr(addr[0]),
		.data(data[0]),
		.wr(wr[0]),
		.rd(rd[0]),
		.vblank(vblankirq),
		.lcdc(lcdcirq),
		.tovf(tmrirq),
		.serial(1'b0),
		.buttons(1'b0),
		.master(irq),
		.jaddr(jaddr));
	
	Soundcore sound(
		.core_clk(clk),
		.addr(addr[0]),
		.data(data[0]),
		.rd(rd[0]),
		.wr(wr[0]),
		.snd_data_l(soundl),
		.snd_data_r(soundr));
endmodule