`define REG_A	0
`define REG_B	1
`define REG_C	2
`define REG_D	3
`define REG_E	4
`define REG_F	5
`define REG_H	6
`define REG_L	7
`define REG_SPH	8
`define REG_SPL	9
`define REG_PCH	10
`define REG_PCL	11

`define _A	registers[`REG_A]
`define _B	registers[`REG_B]
`define _C	registers[`REG_C]
`define _D	registers[`REG_D]
`define _E	registers[`REG_E]
`define _F	registers[`REG_F]
`define _H	registers[`REG_H]
`define _L	registers[`REG_L]
`define _SPH	registers[`REG_SPH]
`define _SPL	registers[`REG_SPL]
`define _PCH	registers[`REG_PCH]
`define _PCL	registers[`REG_PCL]
`define _AF	{`_A, `_F}
`define _BC	{`_B, `_C}
`define _DE	{`_D, `_E}
`define _HL	{`_H, `_L}
`define _SP	{`_SPH, `_SPL}
`define _PC	{`_PCH, `_PCL}

`define FLAG_Z	8'b10000000
`define FLAG_N	8'b01000000
`define FLAG_H	8'b00100000
`define FLAG_C	8'b00010000

`define STATE_FETCH		2'h0
`define STATE_DECODE		2'h1
`define STATE_EXECUTE		2'h2
`define STATE_WRITEBACK		2'h3

`define INSN_VOP_INTR		9'b011111100	// 0xFC is grabbed by the fetch if there is an interrupt pending.
`define INSN_RES		9'b110xxxxxx
`define INSN_SET		9'b111xxxxxx

`define INSN_cc_NZ		2'b00
`define INSN_cc_Z		2'b01
`define INSN_cc_NC		2'b10
`define INSN_cc_C		2'b11

`define INSN_reg_A		3'b111
`define INSN_reg_B		3'b000
`define INSN_reg_C		3'b001
`define INSN_reg_D		3'b010
`define INSN_reg_E		3'b011
`define INSN_reg_H		3'b100
`define INSN_reg_L		3'b101
`define INSN_reg_dHL		3'b110
`define INSN_reg16_BC		2'b00
`define INSN_reg16_DE		2'b01
`define INSN_reg16_HL		2'b10
`define INSN_reg16_SP		2'b11
`define INSN_stack_AF		2'b11
`define INSN_stack_BC		2'b00
`define INSN_stack_DE		2'b01
`define INSN_stack_HL		2'b10
`define INSN_alu_ADD		3'b000
`define INSN_alu_ADC		3'b001
`define INSN_alu_SUB		3'b010
`define INSN_alu_SBC		3'b011
`define INSN_alu_AND		3'b100
`define INSN_alu_XOR		3'b101
`define INSN_alu_OR		3'b110
`define INSN_alu_CP		3'b111		// Oh lawd, is dat some CP?
`define INSN_alu_RLC		3'b000
`define INSN_alu_RRC		3'b001
`define INSN_alu_RL		3'b010
`define INSN_alu_RR		3'b011
`define INSN_alu_DA_SLA		3'b100
`define INSN_alu_CPL_SRA	3'b101
`define INSN_alu_SCF_SWAP	3'b110
`define INSN_alu_CCF_SRL	3'b111

`define EXEC_INC_PC 		`_PC <= `_PC + 1;
`define EXEC_NEXTADDR_PCINC	address <= `_PC + 1;
`define EXEC_NEWCYCLE		begin newcycle <= 1; rd <= 1; wr <= 0; end
`define EXEC_NEWCYCLE_TWOBYTE	begin newcycle <= 1; rd <= 1; wr <= 0; twobyte <= 1; end
`ifdef isim
	`define EXEC_WRITE(ad, da)	begin address <= (ad); wdata <= (da); wr <= 1; end
	`define EXEC_READ(ad)		begin address <= (ad); rd <= 1; end
`else
	/* Work around XST's retarded bugs :\ */
	`define EXEC_WRITE(ad, da)	begin address <= (ad); wdata <= (da); wr <= 1; end end
	`define EXEC_READ(ad)		begin address <= (ad); rd <= 1; end end
`endif

module GBZ80Core(
	input clk,
	inout [15:0] bus0address,	/* BUS_* is latched on STATE_FETCH. */
	inout [7:0] bus0data,
	inout bus0wr, bus0rd,
	inout [15:0] bus1address,	/* BUS_* is latched on STATE_FETCH. */
	inout [7:0] bus1data,
	inout bus1wr, bus1rd,
	input irq, output reg irqack, input [7:0] jaddr,
	output reg [1:0] state);

//	reg [1:0] state;					/* State within this bus cycle (see STATE_*). */
	reg [2:0] cycle;					/* Cycle for instructions. */
	
	reg [7:0] registers[11:0];
	
	reg [15:0] address;				/* Address for the next bus operation. */
	
	reg [8:0] opcode;				/* Opcode from the current machine cycle. */

	reg [7:0] rdata, wdata;		/* Read data from this bus cycle, or write data for the next. */
	reg rd, wr, newcycle, twobyte;
	
	reg [7:0] tmp, tmp2;			/* Generic temporary regs. */
	
	reg [7:0] buswdata;
	wire [7:0] busdata;
	
	reg [15:0] busaddress;
	reg buswr, busrd;
	
	reg bootstrap_enb;
	
	wire bus = ((busaddress[15:8] == 8'h00) && bootstrap_enb) || ((busaddress[15:7] == 9'b111111111) && (busaddress != 16'hFFFF))	/* 0 or 1 depending on which bus */
		`ifdef isim
			|| (busaddress === 16'hxxxx) /* To avoid simulator glomulation. */
		`endif
			;
		
	assign bus0address = (bus == 0) ? busaddress : 16'bzzzzzzzzzzzzzzz;
	assign bus1address = (bus == 1) ? busaddress : 16'bzzzzzzzzzzzzzzz;
	assign bus0data = ((bus == 0) && buswr) ? buswdata : 8'bzzzzzzzz;
	assign bus1data = ((bus == 1) && buswr) ? buswdata : 8'bzzzzzzzz;
	assign busdata = (bus == 0) ? bus0data : bus1data;
	assign bus0rd = (bus == 0) ? busrd : 1'b0;
	assign bus1rd = (bus == 1) ? busrd : 1'b0;
	assign bus0wr = (bus == 0) ? buswr : 1'b0;
	assign bus1wr = (bus == 1) ? buswr : 1'b0;

	reg ie, iedelay;

`define LOCALWIRES
`include "allinsns.v"
`undef LOCALWIRES

	initial begin
		`_A <= 0;
		`_B <= 0;
		`_C <= 0;
		`_D <= 0;
		`_E <= 0;
		`_F <= 0;
		`_H <= 0;
		`_L <= 0;
		`_PCH <= 0;
		`_PCL <= 0;
		`_SPH <= 0;
		`_SPL <= 0;
		rd <= 1;
		wr <= 0;
		newcycle <= 1;
		state <= 0;
		cycle <= 0;
		busrd <= 0;
		buswr <= 0;
		busaddress <= 0;
		ie <= 0;
		iedelay <= 0;
		opcode <= 0;
		state <= `STATE_WRITEBACK;
		cycle <= 0;
		twobyte <= 0;
		bootstrap_enb <= 1;
		irqack <= 0;
	end

	always @(negedge clk)	/* Set things up at the negedge to prepare for the posedge. */
		case (state)
		`STATE_FETCH: begin
			if (newcycle) begin
				busaddress <= `_PC;
				buswr <= 0;
				busrd <= 1;
			end else begin
				busaddress <= address;
				buswr <= wr;
				busrd <= rd;
				if (wr) begin
					buswdata <= wdata;
					if (address == 16'hFF50)
						bootstrap_enb <= 0;
				end
			end
		end
		`STATE_DECODE: begin	/* Make sure this only happens for one clock. */
			buswr <= 0;
			busrd <= 0;
		end
		endcase
	
	always @(posedge clk)
		case (state)
		`STATE_FETCH: begin
			/* Things are set up in negedge so that something looking on posedge will get his shit. */
			state <= `STATE_DECODE;
		end
		`STATE_DECODE: begin
			if (newcycle) begin
				if (twobyte) begin
					opcode <= {1'b1,busdata};
					twobyte <= 0;
				end else if (ie && irq)
					opcode <= `INSN_VOP_INTR;
				else
					opcode <= {1'b0,busdata};
				newcycle <= 0;
				rdata <= busdata;
				cycle <= 0;
			end else begin
				if (rd) rdata <= busdata;	/* Still valid because peripherals are now expected to keep it held valid. */
				cycle <= cycle + 1;
			end
			if (iedelay) begin
				ie <= 1;
				iedelay <= 0;
			end
			wr <= 0;
			rd <= 0;
`ifdef isim
			address <= 16'bxxxxxxxxxxxxxxxx;	// Make it obvious if something of type has happened.
			wdata <= 8'bxxxxxxxx;
`endif
			state <= `STATE_EXECUTE;
		end
		`STATE_EXECUTE: begin
		`ifdef isim
			if (opcode[7:0] === 8'bxxxxxxxx)
				$stop;
		`endif
			casex (opcode)
			`define EXECUTE
			`include "allinsns.v"
			`undef EXECUTE
			default:
			begin
				address <= {7'h78,opcode};	// Have the CPU tell you F0xx if something's gone wrong.
				$stop;
			end
			endcase
			state <= `STATE_WRITEBACK;
		end
		`STATE_WRITEBACK: begin
			casex (opcode)
			`define WRITEBACK
			`include "allinsns.v"
			`undef WRITEBACK
			default:
				$stop;
			endcase
			state <= `STATE_FETCH;
		end
		endcase
endmodule