[fpgaboy.git] / GBZ80Core.v

`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 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_LD_reg_imm8	8'b00xxx110
`define INSN_HALT				8'b01110110
`define INSN_LD_HL_reg		8'b01110xxx
`define INSN_LD_reg_HL		8'b01xxx110
`define INSN_LD_reg_reg		8'b01xxxxxx
`define INSN_LD_reg_imm16	8'b00xx0001
`define INSN_LD_SP_HL		8'b11111001
`define INSN_PUSH_reg		8'b11xx0101
`define INSN_POP_reg			8'b11xx0001
`define INSN_LDH_AC			8'b111x0010	// Either LDH A,(C) or LDH (C),A
`define INSN_LDx_AHL			8'b001xx010	// LDD/LDI A,(HL) / (HL),A
`define INSN_ALU8				8'b10xxxxxx	// 10 xxx yyy

`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?

module GBZ80Core(
	input clk,
	output reg [15:0] busaddress,	/* BUS_* is latched on STATE_FETCH. */
	inout [7:0] busdata,
	output reg buswr, output reg busrd);
	
	reg [1:0] state = 0;					/* State within this bus cycle (see STATE_*). */
	reg [2:0] cycle = 0;					/* Cycle for instructions. */
	
	reg [7:0] registers[11:0];
	
	reg [15:0] address;				/* Address for the next bus operation. */
	
	reg [7:0] 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 = 1, wr = 0, newcycle = 1;
	
	reg [7:0] tmp;					/* Generic temporary reg. */
	
	reg [7:0] buswdata;
	assign busdata = buswr ? buswdata : 8'bzzzzzzzz;
	
	initial begin
		registers[ 0] <= 0;
		registers[ 1] <= 0;
		registers[ 2] <= 0;
		registers[ 3] <= 0;
		registers[ 4] <= 0;
		registers[ 5] <= 0;
		registers[ 6] <= 0;
		registers[ 7] <= 0;
		registers[ 8] <= 0;
		registers[ 9] <= 0;
		registers[10] <= 0;
		registers[11] <= 0;
	end

	always @(posedge clk)
		case (state)
		`STATE_FETCH: begin
			if (wr)
				buswdata <= wdata;
			if (newcycle)
				busaddress <= {registers[`REG_PCH], registers[`REG_PCL]};
			else
				busaddress <= address;
			buswr <= wr;
			busrd <= rd;
			state <= `STATE_DECODE;
		end
		`STATE_DECODE: begin
			if (newcycle) begin
				opcode <= busdata;
				rdata <= busdata;
				newcycle <= 0;
				cycle <= 0;
			end else
				if (rd) rdata <= busdata;
			buswr <= 0;
			busrd <= 0;
			wr <= 0;
			rd <= 0;
			address <= 16'bxxxxxxxxxxxxxxxx;	// Make it obvious if something of type has happened.
			wdata <= 8'bxxxxxxxx;
			state <= `STATE_EXECUTE;
		end
		`STATE_EXECUTE: begin
`define EXEC_INC_PC \
	{registers[`REG_PCH], registers[`REG_PCL]} <= {registers[`REG_PCH], registers[`REG_PCL]} + 1
`define EXEC_NEXTADDR_PCINC \
	address <= {registers[`REG_PCH], registers[`REG_PCL]} + 1
`define EXEC_NEWCYCLE \
	newcycle <= 1; rd <= 1; wr <= 0
			casex (opcode)
			`INSN_LD_reg_imm8: begin
				case (cycle)
				0:	begin
						`EXEC_INC_PC;
						`EXEC_NEXTADDR_PCINC;
						rd <= 1;
					end
				1: begin
						`EXEC_INC_PC;
						if (opcode[5:3] == `INSN_reg_dHL) begin
							address <= {registers[`REG_H], registers[`REG_L]};
							wdata <= rdata;
							rd <= 0;
							wr <= 1;
						end else begin
							`EXEC_NEWCYCLE;
						end
					end
				2: begin
						`EXEC_NEWCYCLE;
					end
				endcase
			end
			`INSN_HALT: begin
				`EXEC_NEWCYCLE;
				/* XXX Interrupts needed for HALT. */
			end
			`INSN_LD_HL_reg: begin
				case (cycle)
				0:	begin
						case (opcode[2:0])
						`INSN_reg_A:	begin wdata <= registers[`REG_A]; end
						`INSN_reg_B:	begin wdata <= registers[`REG_B]; end
						`INSN_reg_C:	begin wdata <= registers[`REG_C]; end
						`INSN_reg_D:	begin wdata <= registers[`REG_D]; end
						`INSN_reg_E:	begin wdata <= registers[`REG_E]; end
						`INSN_reg_H:	begin wdata <= registers[`REG_H]; end
						`INSN_reg_L:	begin wdata <= registers[`REG_L]; end
						endcase
						address <= {registers[`REG_H], registers[`REG_L]};
						wr <= 1; rd <= 0;
					end
				1:	begin
						`EXEC_INC_PC;
						`EXEC_NEWCYCLE;
					end
				endcase
			end
			`INSN_LD_reg_HL: begin
				case(cycle)
				0: begin
						address <= {registers[`REG_H], registers[`REG_L]};
						rd <= 1;
					end
				1: begin
						tmp <= rdata;
						`EXEC_INC_PC;
						`EXEC_NEWCYCLE;
					end
				endcase
			end
			`INSN_LD_reg_reg: begin
				`EXEC_INC_PC;
				`EXEC_NEWCYCLE;
				case (opcode[2:0])
				`INSN_reg_A:	begin tmp <= registers[`REG_A]; end
				`INSN_reg_B:	begin tmp <= registers[`REG_B]; end
				`INSN_reg_C:	begin tmp <= registers[`REG_C]; end
				`INSN_reg_D:	begin tmp <= registers[`REG_D]; end
				`INSN_reg_E:	begin tmp <= registers[`REG_E]; end
				`INSN_reg_H:	begin tmp <= registers[`REG_H]; end
				`INSN_reg_L:	begin tmp <= registers[`REG_L]; end
				endcase
			end
			`INSN_LD_reg_imm16: begin
				`EXEC_INC_PC;
				case (cycle)
				0:	begin
						`EXEC_NEXTADDR_PCINC;
						rd <= 1;
					end
				1:	begin
						`EXEC_NEXTADDR_PCINC;
						rd <= 1;
					end
				2: begin `EXEC_NEWCYCLE; end
				endcase
			end
			`INSN_LD_SP_HL: begin
				case (cycle)
				0:	begin
						tmp <= registers[`REG_H];
					end
				1:	begin
						`EXEC_NEWCYCLE;
						`EXEC_INC_PC;
						tmp <= registers[`REG_L];
					end
				endcase
			end
			`INSN_PUSH_reg: begin	/* PUSH is 16 cycles! */
				case (cycle)
				0: begin
						wr <= 1;
						address <= {registers[`REG_SPH],registers[`REG_SPL]}-1;
						case (opcode[5:4])
						`INSN_stack_AF:	wdata <= registers[`REG_A];
						`INSN_stack_BC:	wdata <= registers[`REG_B];
						`INSN_stack_DE:	wdata <= registers[`REG_D];
						`INSN_stack_HL:	wdata <= registers[`REG_H];
						endcase
					end
				1: begin
						wr <= 1;
						address <= {registers[`REG_SPH],registers[`REG_SPL]}-1;
						case (opcode[5:4])
						`INSN_stack_AF:	wdata <= registers[`REG_F];
						`INSN_stack_BC:	wdata <= registers[`REG_C];
						`INSN_stack_DE:	wdata <= registers[`REG_E];
						`INSN_stack_HL:	wdata <= registers[`REG_L];
						endcase
					end
				2:	begin /* TWIDDLE OUR FUCKING THUMBS! */ end
				3: begin
						`EXEC_NEWCYCLE;
						`EXEC_INC_PC;
					end
				endcase
			end
			`INSN_POP_reg: begin	/* POP is 12 cycles! */
				case (cycle)
				0: begin
						rd <= 1;
						address <= {registers[`REG_SPH],registers[`REG_SPL]};
					end
				1: begin
						rd <= 1;
						address <= {registers[`REG_SPH],registers[`REG_SPL]};
					end
				2: begin
						`EXEC_NEWCYCLE;
						`EXEC_INC_PC;
					end
				endcase
			end
			`INSN_LDH_AC: begin
				case (cycle)
				0:	begin
						address <= {8'hFF,registers[`REG_C]};
						if (opcode[4]) begin	// LD A,(C)
							rd <= 1;
						end else begin
							wr <= 1;
							wdata <= registers[`REG_A];
						end
					end
				1: begin
						`EXEC_NEWCYCLE;
						`EXEC_INC_PC;
					end
				endcase
			end
			`INSN_LDx_AHL: begin
				case (cycle)
				0: begin
						address <= {registers[`REG_H],registers[`REG_L]};
						if (opcode[3]) begin	// LDx A, (HL)
							rd <= 1;
						end else begin
							wr <= 1;
							wdata <= registers[`REG_A];
						end
					end
				1:	begin
						`EXEC_NEWCYCLE;
						`EXEC_INC_PC;
					end
				endcase
			end
			`INSN_ALU8: begin
				if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0)) begin
					// fffffffff fuck your shit, read from (HL) :(
					rd <= 1;
					address <= {registers[`REG_H], registers[`REG_L]};
				end else begin
					`EXEC_NEWCYCLE;
					`EXEC_INC_PC;
					case (opcode[2:0])
					`INSN_reg_A:	begin tmp <= registers[`REG_A]; end
					`INSN_reg_B:	begin tmp <= registers[`REG_B]; end
					`INSN_reg_C:	begin tmp <= registers[`REG_C]; end
					`INSN_reg_D:	begin tmp <= registers[`REG_D]; end
					`INSN_reg_E:	begin tmp <= registers[`REG_E]; end
					`INSN_reg_H:	begin tmp <= registers[`REG_H]; end
					`INSN_reg_L:	begin tmp <= registers[`REG_L]; end
					`INSN_reg_dHL:	begin tmp <= rdata; end
					endcase
				end
			end
			default:
				$stop;
			endcase
			state <= `STATE_WRITEBACK;
		end
		`STATE_WRITEBACK: begin
			casex (opcode)
			`INSN_LD_reg_imm8:
				case (cycle)
				0: cycle <= 1;
				1: case (opcode[5:3])
					`INSN_reg_A:	begin registers[`REG_A] <= rdata; cycle <= 0; end
					`INSN_reg_B:	begin registers[`REG_B] <= rdata; cycle <= 0; end
					`INSN_reg_C:	begin registers[`REG_C] <= rdata; cycle <= 0; end
					`INSN_reg_D:	begin registers[`REG_D] <= rdata; cycle <= 0; end
					`INSN_reg_E:	begin registers[`REG_E] <= rdata; cycle <= 0; end
					`INSN_reg_H:	begin registers[`REG_H] <= rdata; cycle <= 0; end
					`INSN_reg_L:	begin registers[`REG_L] <= rdata; cycle <= 0; end
					`INSN_reg_dHL:	cycle <= 2;
					endcase
				2: cycle <= 0;
				endcase
			`INSN_HALT: begin
				/* Nothing needs happen here. */
				/* XXX Interrupts needed for HALT. */
			end
			`INSN_LD_HL_reg: begin
				case (cycle)
				0: cycle <= 1;
				1: cycle <= 0;
				endcase
			end
			`INSN_LD_reg_HL: begin
				case (cycle)
				0:	cycle <= 1;
				1:	begin
						case (opcode[5:3])
						`INSN_reg_A:	begin registers[`REG_A] <= tmp; end
						`INSN_reg_B:	begin registers[`REG_B] <= tmp; end
						`INSN_reg_C:	begin registers[`REG_C] <= tmp; end
						`INSN_reg_D:	begin registers[`REG_D] <= tmp; end
						`INSN_reg_E:	begin registers[`REG_E] <= tmp; end
						`INSN_reg_H:	begin registers[`REG_H] <= tmp; end
						`INSN_reg_L:	begin registers[`REG_L] <= tmp; end
						endcase
						cycle <= 0;
					end
				endcase
			end
			`INSN_LD_reg_reg: begin
				case (opcode[5:3])
				`INSN_reg_A:	begin registers[`REG_A] <= tmp; end
				`INSN_reg_B:	begin registers[`REG_B] <= tmp; end
				`INSN_reg_C:	begin registers[`REG_C] <= tmp; end
				`INSN_reg_D:	begin registers[`REG_D] <= tmp; end
				`INSN_reg_E:	begin registers[`REG_E] <= tmp; end
				`INSN_reg_H:	begin registers[`REG_H] <= tmp; end
				`INSN_reg_L:	begin registers[`REG_L] <= tmp; end
				endcase
			end
			`INSN_LD_reg_imm16: begin
				case (cycle)
				0:	cycle <= 1;
				1:	begin
						case (opcode[5:4])
						`INSN_reg16_BC:	registers[`REG_C] <= rdata;
						`INSN_reg16_DE:	registers[`REG_E] <= rdata;
						`INSN_reg16_HL:	registers[`REG_L] <= rdata;
						`INSN_reg16_SP:	registers[`REG_SPL] <= rdata;
						endcase
						cycle <= 2;
					end
				2: begin
						case (opcode[5:4])
						`INSN_reg16_BC:	registers[`REG_B] <= rdata;
						`INSN_reg16_DE:	registers[`REG_D] <= rdata;
						`INSN_reg16_HL:	registers[`REG_H] <= rdata;
						`INSN_reg16_SP:	registers[`REG_SPH] <= rdata;
						endcase
						cycle <= 0;
					end
				endcase
			end
			`INSN_LD_SP_HL: begin
				case (cycle)
				0: begin
						cycle <= 1;
						registers[`REG_SPH] <= tmp;
					end
				1: begin
						cycle <= 0;
						registers[`REG_SPL] <= tmp;
					end
				endcase
			end
			`INSN_PUSH_reg: begin	/* PUSH is 16 cycles! */
				case (cycle)
				0: begin
						{registers[`REG_SPH],registers[`REG_SPL]} <=
							{registers[`REG_SPH],registers[`REG_SPL]} - 1;
						cycle <= 1;
					end
				1:	begin
						{registers[`REG_SPH],registers[`REG_SPL]} <=
							{registers[`REG_SPH],registers[`REG_SPL]} - 1;
						cycle <= 2;
					end
				2:	cycle <= 3;
				3:	cycle <= 0;
				endcase
			end
			`INSN_POP_reg: begin	/* POP is 12 cycles! */
				case (cycle)
				0:	begin
						cycle <= 1;
						{registers[`REG_SPH],registers[`REG_SPL]} <=
							{registers[`REG_SPH],registers[`REG_SPL]} + 1;
					end
				1:	begin
						case (opcode[5:4])
						`INSN_stack_AF:	registers[`REG_F] <= rdata;
						`INSN_stack_BC:	registers[`REG_C] <= rdata;
						`INSN_stack_DE:	registers[`REG_E] <= rdata;
						`INSN_stack_HL:	registers[`REG_L] <= rdata;
						endcase
						{registers[`REG_SPH],registers[`REG_SPL]} <=
							{registers[`REG_SPH],registers[`REG_SPL]} + 1;
						cycle <= 2;
					end
				2:	begin
						case (opcode[5:4])
						`INSN_stack_AF:	registers[`REG_A] <= rdata;
						`INSN_stack_BC:	registers[`REG_B] <= rdata;
						`INSN_stack_DE:	registers[`REG_D] <= rdata;
						`INSN_stack_HL:	registers[`REG_H] <= rdata;
						endcase
						cycle <= 0;
					end
				endcase
			end
			`INSN_LDH_AC: begin
				case (cycle)
				0:	cycle <= 1;
				1: begin
						cycle <= 0;
						if (opcode[4])
							registers[`REG_A] <= rdata;
					end
				endcase
			end
			`INSN_LDx_AHL: begin
				case (cycle)
				0:	cycle <= 1;
				1:	begin
						cycle <= 0;
						if (opcode[3])
							registers[`REG_A] <= rdata;
						{registers[`REG_H],registers[`REG_L]} <=
							opcode[4] ? // if set, LDD, else LDI
							({registers[`REG_H],registers[`REG_L]} - 1) :
							({registers[`REG_H],registers[`REG_L]} + 1);
					end
				endcase
			end
			`INSN_ALU8: begin
				if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0)) begin
					/* Sit on our asses. */
					cycle <= 1;
				end else begin		/* Actually do the computation! */
					case (opcode[5:3])
					`INSN_alu_ADD: begin
						registers[`REG_A] <=
							registers[`REG_A] + tmp;
						registers[`REG_F] <=
							{ /* Z */ ((registers[`REG_A] + tmp) == 0) ? 1'b1 : 1'b0,
							  /* N */ 0,
							  /* H */ (({1'b0,registers[`REG_A][3:0]} + {1'b0,tmp[3:0]}) >> 4 == 1) ? 1'b1 : 1'b0,
							  /* C */ (({1'b0,registers[`REG_A]} + {1'b0,tmp}) >> 8 == 1) ? 1'b1 : 1'b0,
							  registers[`REG_F][3:0]
							};
					end
					`INSN_alu_ADC: begin
						registers[`REG_A] <=
							registers[`REG_A] + tmp + {7'b0,registers[`REG_F][4]};
						registers[`REG_F] <=
							{ /* Z */ ((registers[`REG_A] + tmp + {7'b0,registers[`REG_F][4]}) == 0) ? 1'b1 : 1'b0,
							  /* N */ 0,
							  /* H */ (({1'b0,registers[`REG_A][3:0]} + {1'b0,tmp[3:0]} + {4'b0,registers[`REG_F][4]}) >> 4 == 1) ? 1'b1 : 1'b0,
							  /* C */ (({1'b0,registers[`REG_A]} + {1'b0,tmp} + {8'b0,registers[`REG_F][4]}) >> 8 == 1) ? 1'b1 : 1'b0,
							  registers[`REG_F][3:0]
							};
					end
					`INSN_alu_AND: begin
						registers[`REG_A] <=
							registers[`REG_A] & tmp;
						registers[`REG_F] <=
							{ /* Z */ ((registers[`REG_A] & tmp) == 0) ? 1'b1 : 1'b0,
							  0,1,0,
							  registers[`REG_F][3:0]
							};
					end
					`INSN_alu_OR: begin
						registers[`REG_A] <=
							registers[`REG_A] | tmp;
						registers[`REG_F] <=
							{ /* Z */ ((registers[`REG_A] | tmp) == 0) ? 1'b1 : 1'b0,
							  0,0,0,
							  registers[`REG_F][3:0]
							};
					end
					`INSN_alu_XOR: begin
						registers[`REG_A] <=
							registers[`REG_A] ^ tmp;
						registers[`REG_F] <=
							{ /* Z */ ((registers[`REG_A] ^ tmp) == 0) ? 1'b1 : 1'b0,
							  0,0,0,
							  registers[`REG_F][3:0]
							};
					end
					default:
						$stop;
					endcase
				end
			end
			endcase
			state <= `STATE_FETCH;
		end
		endcase
endmodule

`timescale 1ns / 1ps
module TestBench();
	reg clk = 0;
	wire [15:0] addr;
	wire [7:0] data;
	wire wr, rd;
	reg [7:0] rom [2047:0];
	
	initial $readmemh("rom.hex", rom);
	always #10 clk <= ~clk;
	GBZ80Core core(
		.clk(clk),
		.busaddress(addr),
		.busdata(data),
		.buswr(wr),
		.busrd(rd));
	assign data = rd ? rom[addr] : 8'bzzzzzzzz;
endmodule
Commit	Line	Data
2f55f809 JW	1	`define REG_A 0
	2	`define REG_B 1
	3	`define REG_C 2
	4	`define REG_D 3
	5	`define REG_E 4
	6	`define REG_F 5
	7	`define REG_H 6
	8	`define REG_L 7
	9	`define REG_SPH 8
	10	`define REG_SPL 9
	11	`define REG_PCH 10
	12	`define REG_PCL 11
	13
	14	`define FLAG_Z 8'b10000000
	15	`define FLAG_N 8'b01000000
	16	`define FLAG_H 8'b00100000
	17	`define FLAG_C 8'b00010000
	18
	19	`define STATE_FETCH 2'h0
	20	`define STATE_DECODE 2'h1
	21	`define STATE_EXECUTE 2'h2
	22	`define STATE_WRITEBACK 2'h3
	23
	24	`define INSN_LD_reg_imm8 8'b00xxx110
b85870e0 JW	25	`define INSN_HALT 8'b01110110
	26	`define INSN_LD_HL_reg 8'b01110xxx
	27	`define INSN_LD_reg_HL 8'b01xxx110
	28	`define INSN_LD_reg_reg 8'b01xxxxxx
634ce02c JW	29	`define INSN_LD_reg_imm16 8'b00xx0001
634ce02c JW	30	`define INSN_LD_SP_HL 8'b11111001
97649fed	31	`define INSN_PUSH_reg 8'b11xx0101
00e30b4d JW	32	`define INSN_POP_reg 8'b11xx0001
00e30b4d JW	33	`define INSN_LDH_AC 8'b111x0010 // Either LDH A,(C) or LDH (C),A
fa136d63	34	`define INSN_LDx_AHL 8'b001xx010 // LDD/LDI A,(HL) / (HL),A
94522011	35	`define INSN_ALU8 8'b10xxxxxx // 10 xxx yyy
fa136d63	36
b85870e0 JW	37	`define INSN_reg_A 3'b111
	38	`define INSN_reg_B 3'b000
	39	`define INSN_reg_C 3'b001
	40	`define INSN_reg_D 3'b010
	41	`define INSN_reg_E 3'b011
	42	`define INSN_reg_H 3'b100
	43	`define INSN_reg_L 3'b101
	44	`define INSN_reg_dHL 3'b110
634ce02c JW	45	`define INSN_reg16_BC 2'b00
	46	`define INSN_reg16_DE 2'b01
	47	`define INSN_reg16_HL 2'b10
	48	`define INSN_reg16_SP 2'b11
97649fed JW	49	`define INSN_stack_AF 2'b11
	50	`define INSN_stack_BC 2'b00
	51	`define INSN_stack_DE 2'b01
	52	`define INSN_stack_HL 2'b10
94522011 JW	53	`define INSN_alu_ADD 3'b000
	54	`define INSN_alu_ADC 3'b001
	55	`define INSN_alu_SUB 3'b010
	56	`define INSN_alu_SBC 3'b011
	57	`define INSN_alu_AND 3'b100
	58	`define INSN_alu_XOR 3'b101
	59	`define INSN_alu_OR 3'b110
	60	`define INSN_alu_CP 3'b111 // Oh lawd, is dat some CP?
	61
2f55f809 JW	62	module GBZ80Core(
	63	input clk,
	64	output reg [15:0] busaddress, /* BUS_* is latched on STATE_FETCH. */
	65	inout [7:0] busdata,
	66	output reg buswr, output reg busrd);
	67
	68	reg [1:0] state = 0; /* State within this bus cycle (see STATE_). /
	69	reg [2:0] cycle = 0; /* Cycle for instructions. */
	70
	71	reg [7:0] registers[11:0];
	72
	73	reg [15:0] address; /* Address for the next bus operation. */
	74
	75	reg [7:0] opcode; /* Opcode from the current machine cycle. */
	76
	77	reg [7:0] rdata, wdata; /* Read data from this bus cycle, or write data for the next. */
	78	reg rd = 1, wr = 0, newcycle = 1;
	79
b85870e0 JW	80	reg [7:0] tmp; /* Generic temporary reg. */
b85870e0 JW	81
2f55f809 JW	82	reg [7:0] buswdata;
	83	assign busdata = buswr ? buswdata : 8'bzzzzzzzz;
	84
	85	initial begin
241c995c JW	86	registers[ 0] <= 0;
	87	registers[ 1] <= 0;
	88	registers[ 2] <= 0;
	89	registers[ 3] <= 0;
	90	registers[ 4] <= 0;
	91	registers[ 5] <= 0;
	92	registers[ 6] <= 0;
	93	registers[ 7] <= 0;
	94	registers[ 8] <= 0;
	95	registers[ 9] <= 0;
	96	registers[10] <= 0;
	97	registers[11] <= 0;
2f55f809 JW	98	end
	99
	100	always @(posedge clk)
	101	case (state)
	102	`STATE_FETCH: begin
	103	if (wr)
	104	buswdata <= wdata;
	105	if (newcycle)
	106	busaddress <= {registers[`REG_PCH], registers[`REG_PCL]};
	107	else
	108	busaddress <= address;
	109	buswr <= wr;
	110	busrd <= rd;
	111	state <= `STATE_DECODE;
	112	end
	113	`STATE_DECODE: begin
	114	if (newcycle) begin
	115	opcode <= busdata;
	116	rdata <= busdata;
b85870e0	117	newcycle <= 0;
2f55f809 JW	118	cycle <= 0;
	119	end else
	120	if (rd) rdata <= busdata;
	121	buswr <= 0;
	122	busrd <= 0;
97649fed JW	123	wr <= 0;
	124	rd <= 0;
	125	address <= 16'bxxxxxxxxxxxxxxxx; // Make it obvious if something of type has happened.
	126	wdata <= 8'bxxxxxxxx;
2f55f809 JW	127	state <= `STATE_EXECUTE;
	128	end
	129	`STATE_EXECUTE: begin
	130	`define EXEC_INC_PC \
	131	{registers[`REG_PCH], registers[`REG_PCL]} <= {registers[`REG_PCH], registers[`REG_PCL]} + 1
	132	`define EXEC_NEXTADDR_PCINC \
	133	address <= {registers[`REG_PCH], registers[`REG_PCL]} + 1
	134	`define EXEC_NEWCYCLE \
	135	newcycle <= 1; rd <= 1; wr <= 0
	136	casex (opcode)
	137	`INSN_LD_reg_imm8: begin
	138	case (cycle)
	139	0: begin
	140	`EXEC_INC_PC;
	141	`EXEC_NEXTADDR_PCINC;
2f55f809 JW	142	rd <= 1;
	143	end
	144	1: begin
	145	`EXEC_INC_PC;
b85870e0	146	if (opcode[5:3] == `INSN_reg_dHL) begin
2f55f809 JW	147	address <= {registers[`REG_H], registers[`REG_L]};
	148	wdata <= rdata;
	149	rd <= 0;
	150	wr <= 1;
	151	end else begin
	152	`EXEC_NEWCYCLE;
	153	end
	154	end
	155	2: begin
	156	`EXEC_NEWCYCLE;
	157	end
	158	endcase
	159	end
b85870e0	160	`INSN_HALT: begin
f2e04715 JW	161	`EXEC_NEWCYCLE;
f2e04715 JW	162	/* XXX Interrupts needed for HALT. */
b85870e0 JW	163	end
b85870e0 JW	164	`INSN_LD_HL_reg: begin
f2e04715 JW	165	case (cycle)
	166	0: begin
	167	case (opcode[2:0])
	168	`INSN_reg_A: begin wdata <= registers[`REG_A]; end
	169	`INSN_reg_B: begin wdata <= registers[`REG_B]; end
	170	`INSN_reg_C: begin wdata <= registers[`REG_C]; end
	171	`INSN_reg_D: begin wdata <= registers[`REG_D]; end
	172	`INSN_reg_E: begin wdata <= registers[`REG_E]; end
	173	`INSN_reg_H: begin wdata <= registers[`REG_H]; end
	174	`INSN_reg_L: begin wdata <= registers[`REG_L]; end
	175	endcase
	176	address <= {registers[`REG_H], registers[`REG_L]};
	177	wr <= 1; rd <= 0;
	178	end
	179	1: begin
	180	`EXEC_INC_PC;
	181	`EXEC_NEWCYCLE;
	182	end
	183	endcase
b85870e0 JW	184	end
b85870e0 JW	185	`INSN_LD_reg_HL: begin
f2e04715 JW	186	case(cycle)
	187	0: begin
	188	address <= {registers[`REG_H], registers[`REG_L]};
97649fed	189	rd <= 1;
f2e04715 JW	190	end
	191	1: begin
	192	tmp <= rdata;
	193	`EXEC_INC_PC;
	194	`EXEC_NEWCYCLE;
	195	end
	196	endcase
b85870e0 JW	197	end
	198	`INSN_LD_reg_reg: begin
	199	`EXEC_INC_PC;
	200	`EXEC_NEWCYCLE;
	201	case (opcode[2:0])
	202	`INSN_reg_A: begin tmp <= registers[`REG_A]; end
	203	`INSN_reg_B: begin tmp <= registers[`REG_B]; end
	204	`INSN_reg_C: begin tmp <= registers[`REG_C]; end
	205	`INSN_reg_D: begin tmp <= registers[`REG_D]; end
	206	`INSN_reg_E: begin tmp <= registers[`REG_E]; end
	207	`INSN_reg_H: begin tmp <= registers[`REG_H]; end
	208	`INSN_reg_L: begin tmp <= registers[`REG_L]; end
	209	endcase
	210	end
634ce02c JW	211	`INSN_LD_reg_imm16: begin
	212	`EXEC_INC_PC;
	213	case (cycle)
	214	0: begin
	215	`EXEC_NEXTADDR_PCINC;
	216	rd <= 1;
	217	end
	218	1: begin
	219	`EXEC_NEXTADDR_PCINC;
	220	rd <= 1;
	221	end
	222	2: begin `EXEC_NEWCYCLE; end
	223	endcase
	224	end
	225	`INSN_LD_SP_HL: begin
	226	case (cycle)
	227	0: begin
634ce02c JW	228	tmp <= registers[`REG_H];
	229	end
	230	1: begin
	231	`EXEC_NEWCYCLE;
	232	`EXEC_INC_PC;
	233	tmp <= registers[`REG_L];
	234	end
	235	endcase
	236	end
97649fed JW	237	`INSN_PUSH_reg: begin /* PUSH is 16 cycles! */
	238	case (cycle)
	239	0: begin
	240	wr <= 1;
	241	address <= {registers[`REG_SPH],registers[`REG_SPL]}-1;
	242	case (opcode[5:4])
	243	`INSN_stack_AF: wdata <= registers[`REG_A];
	244	`INSN_stack_BC: wdata <= registers[`REG_B];
	245	`INSN_stack_DE: wdata <= registers[`REG_D];
	246	`INSN_stack_HL: wdata <= registers[`REG_H];
	247	endcase
	248	end
	249	1: begin
	250	wr <= 1;
	251	address <= {registers[`REG_SPH],registers[`REG_SPL]}-1;
	252	case (opcode[5:4])
	253	`INSN_stack_AF: wdata <= registers[`REG_F];
	254	`INSN_stack_BC: wdata <= registers[`REG_C];
	255	`INSN_stack_DE: wdata <= registers[`REG_E];
	256	`INSN_stack_HL: wdata <= registers[`REG_L];
	257	endcase
	258	end
	259	2: begin /* TWIDDLE OUR FUCKING THUMBS! */ end
	260	3: begin
	261	`EXEC_NEWCYCLE;
	262	`EXEC_INC_PC;
	263	end
	264	endcase
	265	end
	266	`INSN_POP_reg: begin /* POP is 12 cycles! */
	267	case (cycle)
	268	0: begin
	269	rd <= 1;
	270	address <= {registers[`REG_SPH],registers[`REG_SPL]};
	271	end
	272	1: begin
	273	rd <= 1;
	274	address <= {registers[`REG_SPH],registers[`REG_SPL]};
	275	end
	276	2: begin
	277	`EXEC_NEWCYCLE;
	278	`EXEC_INC_PC;
	279	end
	280	endcase
	281	end
00e30b4d JW	282	`INSN_LDH_AC: begin
	283	case (cycle)
	284	0: begin
	285	address <= {8'hFF,registers[`REG_C]};
	286	if (opcode[4]) begin // LD A,(C)
	287	rd <= 1;
	288	end else begin
	289	wr <= 1;
fa136d63	290	wdata <= registers[`REG_A];
00e30b4d JW	291	end
	292	end
	293	1: begin
	294	`EXEC_NEWCYCLE;
	295	`EXEC_INC_PC;
	296	end
	297	endcase
	298	end
fa136d63 JW	299	`INSN_LDx_AHL: begin
	300	case (cycle)
	301	0: begin
	302	address <= {registers[`REG_H],registers[`REG_L]};
	303	if (opcode[3]) begin // LDx A, (HL)
	304	rd <= 1;
	305	end else begin
	306	wr <= 1;
	307	wdata <= registers[`REG_A];
	308	end
	309	end
	310	1: begin
	311	`EXEC_NEWCYCLE;
	312	`EXEC_INC_PC;
	313	end
	314	endcase
	315	end
94522011 JW	316	`INSN_ALU8: begin
	317	if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0)) begin
	318	// fffffffff fuck your shit, read from (HL) :(
	319	rd <= 1;
	320	address <= {registers[`REG_H], registers[`REG_L]};
	321	end else begin
	322	`EXEC_NEWCYCLE;
	323	`EXEC_INC_PC;
	324	case (opcode[2:0])
	325	`INSN_reg_A: begin tmp <= registers[`REG_A]; end
	326	`INSN_reg_B: begin tmp <= registers[`REG_B]; end
	327	`INSN_reg_C: begin tmp <= registers[`REG_C]; end
	328	`INSN_reg_D: begin tmp <= registers[`REG_D]; end
	329	`INSN_reg_E: begin tmp <= registers[`REG_E]; end
	330	`INSN_reg_H: begin tmp <= registers[`REG_H]; end
	331	`INSN_reg_L: begin tmp <= registers[`REG_L]; end
	332	`INSN_reg_dHL: begin tmp <= rdata; end
	333	endcase
	334	end
	335	end
634ce02c JW	336	default:
634ce02c JW	337	$stop;
2f55f809 JW	338	endcase
	339	state <= `STATE_WRITEBACK;
	340	end
	341	`STATE_WRITEBACK: begin
	342	casex (opcode)
634ce02c JW	343	`INSN_LD_reg_imm8:
	344	case (cycle)
	345	0: cycle <= 1;
	346	1: case (opcode[5:3])
	347	`INSN_reg_A: begin registers[`REG_A] <= rdata; cycle <= 0; end
	348	`INSN_reg_B: begin registers[`REG_B] <= rdata; cycle <= 0; end
	349	`INSN_reg_C: begin registers[`REG_C] <= rdata; cycle <= 0; end
	350	`INSN_reg_D: begin registers[`REG_D] <= rdata; cycle <= 0; end
	351	`INSN_reg_E: begin registers[`REG_E] <= rdata; cycle <= 0; end
	352	`INSN_reg_H: begin registers[`REG_H] <= rdata; cycle <= 0; end
	353	`INSN_reg_L: begin registers[`REG_L] <= rdata; cycle <= 0; end
	354	`INSN_reg_dHL: cycle <= 2;
b85870e0	355	endcase
634ce02c JW	356	2: cycle <= 0;
	357	endcase
	358	`INSN_HALT: begin
	359	/* Nothing needs happen here. */
	360	/* XXX Interrupts needed for HALT. */
	361	end
	362	`INSN_LD_HL_reg: begin
	363	case (cycle)
	364	0: cycle <= 1;
	365	1: cycle <= 0;
	366	endcase
	367	end
	368	`INSN_LD_reg_HL: begin
	369	case (cycle)
	370	0: cycle <= 1;
	371	1: begin
	372	case (opcode[5:3])
	373	`INSN_reg_A: begin registers[`REG_A] <= tmp; end
	374	`INSN_reg_B: begin registers[`REG_B] <= tmp; end
	375	`INSN_reg_C: begin registers[`REG_C] <= tmp; end
	376	`INSN_reg_D: begin registers[`REG_D] <= tmp; end
	377	`INSN_reg_E: begin registers[`REG_E] <= tmp; end
	378	`INSN_reg_H: begin registers[`REG_H] <= tmp; end
	379	`INSN_reg_L: begin registers[`REG_L] <= tmp; end
	380	endcase
	381	cycle <= 0;
	382	end
	383	endcase
	384	end
	385	`INSN_LD_reg_reg: begin
	386	case (opcode[5:3])
	387	`INSN_reg_A: begin registers[`REG_A] <= tmp; end
	388	`INSN_reg_B: begin registers[`REG_B] <= tmp; end
	389	`INSN_reg_C: begin registers[`REG_C] <= tmp; end
	390	`INSN_reg_D: begin registers[`REG_D] <= tmp; end
	391	`INSN_reg_E: begin registers[`REG_E] <= tmp; end
	392	`INSN_reg_H: begin registers[`REG_H] <= tmp; end
	393	`INSN_reg_L: begin registers[`REG_L] <= tmp; end
	394	endcase
	395	end
	396	`INSN_LD_reg_imm16: begin
	397	case (cycle)
	398	0: cycle <= 1;
	399	1: begin
	400	case (opcode[5:4])
	401	`INSN_reg16_BC: registers[`REG_C] <= rdata;
	402	`INSN_reg16_DE: registers[`REG_E] <= rdata;
	403	`INSN_reg16_HL: registers[`REG_L] <= rdata;
	404	`INSN_reg16_SP: registers[`REG_SPL] <= rdata;
	405	endcase
	406	cycle <= 2;
	407	end
	408	2: begin
	409	case (opcode[5:4])
	410	`INSN_reg16_BC: registers[`REG_B] <= rdata;
	411	`INSN_reg16_DE: registers[`REG_D] <= rdata;
	412	`INSN_reg16_HL: registers[`REG_H] <= rdata;
	413	`INSN_reg16_SP: registers[`REG_SPH] <= rdata;
	414	endcase
	415	cycle <= 0;
	416	end
	417	endcase
	418	end
	419	`INSN_LD_SP_HL: begin
420	case (cycle)
421	0: begin
422	cycle <= 1;
423	registers[`REG_SPH] <= tmp;
424	end
425	1: begin
426	cycle <= 0;
427	registers[`REG_SPL] <= tmp;
428	end
429	endcase
430	end
97649fed JW	431	`INSN_PUSH_reg: begin /* PUSH is 16 cycles! */
	432	case (cycle)
	433	0: begin
241c995c	434	{registers[`REG_SPH],registers[`REG_SPL]} <=
97649fed JW	435	{registers[`REG_SPH],registers[`REG_SPL]} - 1;
	436	cycle <= 1;
	437	end
	438	1: begin
241c995c	439	{registers[`REG_SPH],registers[`REG_SPL]} <=
97649fed JW	440	{registers[`REG_SPH],registers[`REG_SPL]} - 1;
	441	cycle <= 2;
	442	end
	443	2: cycle <= 3;
	444	3: cycle <= 0;
	445	endcase
	446	end
	447	`INSN_POP_reg: begin /* POP is 12 cycles! */
	448	case (cycle)
	449	0: begin
	450	cycle <= 1;
241c995c	451	{registers[`REG_SPH],registers[`REG_SPL]} <=
97649fed JW	452	{registers[`REG_SPH],registers[`REG_SPL]} + 1;
	453	end
	454	1: begin
	455	case (opcode[5:4])
	456	`INSN_stack_AF: registers[`REG_F] <= rdata;
	457	`INSN_stack_BC: registers[`REG_C] <= rdata;
	458	`INSN_stack_DE: registers[`REG_E] <= rdata;
	459	`INSN_stack_HL: registers[`REG_L] <= rdata;
	460	endcase
241c995c	461	{registers[`REG_SPH],registers[`REG_SPL]} <=
97649fed JW	462	{registers[`REG_SPH],registers[`REG_SPL]} + 1;
	463	cycle <= 2;
	464	end
	465	2: begin
	466	case (opcode[5:4])
	467	`INSN_stack_AF: registers[`REG_A] <= rdata;
	468	`INSN_stack_BC: registers[`REG_B] <= rdata;
	469	`INSN_stack_DE: registers[`REG_D] <= rdata;
	470	`INSN_stack_HL: registers[`REG_H] <= rdata;
	471	endcase
	472	cycle <= 0;
	473	end
	474	endcase
00e30b4d JW	475	end
	476	`INSN_LDH_AC: begin
	477	case (cycle)
	478	0: cycle <= 1;
	479	1: begin
	480	cycle <= 0;
	481	if (opcode[4])
	482	registers[`REG_A] <= rdata;
	483	end
	484	endcase
	485	end
fa136d63 JW	486	`INSN_LDx_AHL: begin
	487	case (cycle)
	488	0: cycle <= 1;
	489	1: begin
	490	cycle <= 0;
	491	if (opcode[3])
	492	registers[`REG_A] <= rdata;
	493	{registers[`REG_H],registers[`REG_L]} <=
	494	opcode[4] ? // if set, LDD, else LDI
	495	({registers[`REG_H],registers[`REG_L]} - 1) :
	496	({registers[`REG_H],registers[`REG_L]} + 1);
	497	end
	498	endcase
	499	end
94522011 JW	500	`INSN_ALU8: begin
	501	if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0)) begin
	502	/* Sit on our asses. */
	503	cycle <= 1;
	504	end else begin /* Actually do the computation! */
	505	case (opcode[5:3])
	506	`INSN_alu_ADD: begin
	507	registers[`REG_A] <=
	508	registers[`REG_A] + tmp;
	509	registers[`REG_F] <=
	510	{ /* Z */ ((registers[`REG_A] + tmp) == 0) ? 1'b1 : 1'b0,
	511	/* N */ 0,
	512	/* H */ (({1'b0,registers[`REG_A][3:0]} + {1'b0,tmp[3:0]}) >> 4 == 1) ? 1'b1 : 1'b0,
	513	/* C */ (({1'b0,registers[`REG_A]} + {1'b0,tmp}) >> 8 == 1) ? 1'b1 : 1'b0,
	514	registers[`REG_F][3:0]
	515	};
	516	end
6dbce0b5 JW	517	`INSN_alu_ADC: begin
	518	registers[`REG_A] <=
	519	registers[`REG_A] + tmp + {7'b0,registers[`REG_F][4]};
	520	registers[`REG_F] <=
	521	{ /* Z */ ((registers[`REG_A] + tmp + {7'b0,registers[`REG_F][4]}) == 0) ? 1'b1 : 1'b0,
	522	/* N */ 0,
	523	/* H */ (({1'b0,registers[`REG_A][3:0]} + {1'b0,tmp[3:0]} + {4'b0,registers[`REG_F][4]}) >> 4 == 1) ? 1'b1 : 1'b0,
	524	/* C */ (({1'b0,registers[`REG_A]} + {1'b0,tmp} + {8'b0,registers[`REG_F][4]}) >> 8 == 1) ? 1'b1 : 1'b0,
	525	registers[`REG_F][3:0]
	526	};
	527	end
	528	`INSN_alu_AND: begin
	529	registers[`REG_A] <=
	530	registers[`REG_A] & tmp;
	531	registers[`REG_F] <=
	532	{ /* Z */ ((registers[`REG_A] & tmp) == 0) ? 1'b1 : 1'b0,
	533	0,1,0,
	534	registers[`REG_F][3:0]
	535	};
	536	end
	537	`INSN_alu_OR: begin
	538	registers[`REG_A] <=
	539	registers[`REG_A] \| tmp;
	540	registers[`REG_F] <=
	541	{ /* Z */ ((registers[`REG_A] \| tmp) == 0) ? 1'b1 : 1'b0,
	542	0,0,0,
	543	registers[`REG_F][3:0]
	544	};
	545	end
	546	`INSN_alu_XOR: begin
	547	registers[`REG_A] <=
	548	registers[`REG_A] ^ tmp;
	549	registers[`REG_F] <=
	550	{ /* Z */ ((registers[`REG_A] ^ tmp) == 0) ? 1'b1 : 1'b0,
	551	0,0,0,
	552	registers[`REG_F][3:0]
	553	};
	554	end
94522011 JW	555	default:
	556	$stop;
	557	endcase
	558	end
	559	end
2f55f809 JW	560	endcase
	561	state <= `STATE_FETCH;
	562	end
	563	endcase
	564	endmodule
	565
	566	`timescale 1ns / 1ps
	567	module TestBench();
	568	reg clk = 0;
	569	wire [15:0] addr;
	570	wire [7:0] data;
	571	wire wr, rd;
	572	reg [7:0] rom [2047:0];
	573
	574	initial $readmemh("rom.hex", rom);
	575	always #10 clk <= ~clk;
	576	GBZ80Core core(
	577	.clk(clk),
	578	.busaddress(addr),
	579	.busdata(data),
	580	.buswr(wr),
	581	.busrd(rd));
	582	assign data = rd ? rom[addr] : 8'bzzzzzzzz;
	583	endmodule