[firearm.git] / Issue.v

`include "ARM_Constants.v"

module Issue(
	input clk,
	input Nrst,	/* XXX not used yet */
	
	input stall,	/* pipeline control */
	input flush,
	
	input inbubble,	/* stage inputs */
	input [31:0] insn,
	input [31:0] inpc,
	input [31:0] cpsr,
	
	output reg outstall,	/* stage outputs */
	output reg outbubble,
	output reg [31:0] outpc,
	output reg [31:0] outinsn
	/* XXX other? */
	);
	

`ifdef COPY_PASTA_FODDER
	/* from page 2 of ARM7TDMIvE2.pdf */
	casex (insn)
	32'b????000000??????????????1001????:	/* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
//	32'b????00001???????????????1001????:	/* Multiply long */
	32'b????00010?001111????000000000000:	/* MRS (Transfer PSR to register) */
	32'b????00010?101001111100000000????:	/* MSR (Transfer register to PSR) */
	32'b????00?10?1010001111????????????:	/* MSR (Transfer register or immediate to PSR, flag bits only) */
	32'b????00??????????????????????????:	/* ALU */
	32'b????00010?00????????00001001????:	/* Atomic swap */
	32'b????000100101111111111110001????:	/* Branch */
	32'b????000??0??????????00001??1????:	/* Halfword transfer - register offset */
	32'b????000??1??????????00001??1????:	/* Halfword transfer - register offset */
	32'b????011????????????????????1????:	/* Undefined. I hate ARM */
	32'b????01??????????????????????????:	/* Single data transfer */
	32'b????100?????????????????????????:	/* Block data transfer */
	32'b????101?????????????????????????:	/* Branch */
	32'b????110?????????????????????????:	/* Coprocessor data transfer */
	32'b????1110???????????????????0????:	/* Coprocessor data op */
	32'b????1110???????????????????1????:	/* Coprocessor register transfer */
	32'b????1111????????????????????????:	/* SWI */
	default:				/* X everything else out */
	endcase
`endif

	/* Flag setting */
	reg use_cpsr;
	reg [15:0] use_regs;
	reg def_cpsr;
	reg [15:0] def_regs;
	
	function [15:0] idxbit;
		input [3:0] r;
		if (r == 15)
			idxbit = 0;
		else
			idxbit = (16'b1) << r;
	endfunction
	
	wire [3:0] rn = insn[19:16];
	wire [3:0] rd = insn[15:12];
	wire [3:0] rs = insn[11:8];
	wire [3:0] rm = insn[3:0];
	wire [3:0] cond = insn[31:28];
	
	wire [3:0] rd_mul = insn[19:16];
	wire [3:0] rn_mul = insn[15:12];
	wire [3:0] rs_mul = insn[11:8];
	
	wire [3:0] alu_opc = insn[24:21];
	
	function alu_is_logical;
		input [3:0] op;
		
		case (op)
		`ALU_AND,`ALU_EOR,`ALU_TST,`ALU_TEQ,`ALU_ORR,`ALU_MOV,`ALU_BIC,`ALU_MVN: alu_is_logical = 1;
		default: alu_is_logical = 0;
		endcase
	endfunction
	
	function alu_flags_only;
		input [3:0] op;
		
		case (op)
		`ALU_TST,`ALU_TEQ,`ALU_CMP,`ALU_CMN: alu_flags_only = 1;
		default: alu_flags_only = 0;
		endcase
	endfunction
	
	function shift_requires_carry;
		input [7:0] shift;
		
		case(shift[1:0])
		`SHIFT_LSL: shift_requires_carry = (shift[7:2] == 0);
		`SHIFT_LSR: shift_requires_carry = 0;
		`SHIFT_ASR: shift_requires_carry = 0;
		`SHIFT_ROR: shift_requires_carry = (shift[7:2] == 0);
		endcase
	endfunction
	
	always @(*)
		casez (insn)
		32'b????000000??????????????1001????:	/* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = (insn[21] /* accum */ ? idxbit(rn_mul) : 0) | idxbit(rs_mul) | idxbit(rm);
			def_cpsr = insn[20] /* setcc */;
			def_regs = idxbit(rd_mul);
		end
//		32'b????00001???????????????1001????:	/* Multiply long */
		32'b????00010?001111????000000000000:	/* MRS (Transfer PSR to register) */
		begin
			use_cpsr = `COND_MATTERS(cond) || (insn[22] == 0) /* Source = CPSR */;
			use_regs = 0;
			def_cpsr = 0;
			def_regs = idxbit(rd);
		end
		32'b????00010?101001111100000000????:	/* MSR (Transfer register to PSR) */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = idxbit(rm);
			def_cpsr = 1;
			def_regs = 0;
		end
		32'b????00?10?1010001111????????????:	/* MSR (Transfer register or immediate to PSR, flag bits only) */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = insn[25] ? 0 : idxbit(rm);
			def_cpsr = 1;
			def_regs = 0;
		end
		32'b????00??????????????????????????:	/* ALU */
		begin
			use_cpsr = `COND_MATTERS(cond) | (!insn[25] /* I */ && shift_requires_carry(insn[11:4]));
			use_regs =
				(insn[25] /* I */ ? 0 :
					(insn[4] /* shift by reg */ ?
						(idxbit(rs) | idxbit(rm)) :
						(idxbit(rm)))) |
				(((alu_opc != `ALU_MOV) && (alu_opc != `ALU_MVN)) ? idxbit(rn) : 0);
			def_cpsr = insn[20] /* S */ | alu_is_logical(alu_opc);
			def_regs = alu_flags_only(alu_opc) ? 0 : idxbit(rd);
		end
		32'b????00010?00????????00001001????:	/* Atomic swap */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = idxbit(rn) | idxbit(rm);
			def_cpsr = 0;
			def_regs = idxbit(rd);
		end
		32'b????000100101111111111110001????:	/* Branch */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = idxbit(rm);
			def_cpsr = 0;	// don't care, we'll never get there
			def_regs = 0;
		end
		32'b????000??0??????????00001??1????:	/* Halfword transfer - register offset */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = idxbit(rn) | idxbit(rm) | (insn[20] /* L */ ? 0 : idxbit(rd));
			def_cpsr = 0;
			def_regs = insn[20] /* L */ ? idxbit(rd) : 0;
		end
		32'b????000??1??????????00001??1????:	/* Halfword transfer - immediate offset */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = idxbit(rn) | (insn[20] /* L */ ? 0 : idxbit(rd));
			def_cpsr = 0;
			def_regs = insn[20] /* L */ ? idxbit(rd) : 0;
		end
		32'b????011????????????????????1????:	/* Undefined. I hate ARM */
		begin	
			use_cpsr = 0;
			use_regs = 0;
			def_cpsr = 0;
			def_regs = 0;
		end
		32'b????100?????????????????????????:	/* Block data transfer */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = idxbit(rn) | (insn[20] /* L */ ? 0 : insn[15:0]);
			def_cpsr = insn[22];	/* This is a superset of all cases, anyway. */
			def_regs = (insn[21] /* W */ ? idxbit(rn) : 0) | (insn[20] /* L */ ? insn[15:0] : 0);
		end
		32'b????101?????????????????????????:	/* Branch */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = 0;
			def_cpsr = 0;
			def_regs = 0;
		end
		32'b????110?????????????????????????:	/* Coprocessor data transfer */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = idxbit(rn);
			def_cpsr = 0;
			def_regs = insn[21] /* W */ ? idxbit(rn) : 0;
		end
		32'b????1110???????????????????0????:	/* Coprocessor data op */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = 0;
			def_cpsr = 0;
			def_regs = 0;
		end
		32'b????1110???????????????????1????:	/* Coprocessor register transfer */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = insn[20] /* L */ ? 0 : idxbit(rd);
			def_cpsr = 0;
			def_regs = insn[20] /* L */ ? idxbit(rd) : 0;
		end
		32'b????1111????????????????????????:	/* SWI */
		begin
			use_cpsr = `COND_MATTERS(cond);
			use_regs = 0;
			def_cpsr = 0;
			def_regs = 0;
		end
		default:				/* X everything else out */
		begin
			use_cpsr = 1'bx;
			use_regs = 16'bxxxxxxxxxxxxxxxx;
			def_cpsr = 1'bx;
			def_regs = 16'bxxxxxxxxxxxxxxxx;
		end
		endcase
	
	/* Condition checking logic */
	reg condition_met;
	always @(*)
		casez(insn[31:28])
		`COND_EQ:	condition_met = cpsr[`CPSR_Z];
		`COND_NE:	condition_met = !cpsr[`CPSR_Z];
		`COND_CS:	condition_met = cpsr[`CPSR_C];
		`COND_CC:	condition_met = !cpsr[`CPSR_C];
		`COND_MI:	condition_met = cpsr[`CPSR_N];
		`COND_PL:	condition_met = !cpsr[`CPSR_N];
		`COND_VS:	condition_met = cpsr[`CPSR_V];
		`COND_VC:	condition_met = !cpsr[`CPSR_V];
		`COND_HI:	condition_met = cpsr[`CPSR_C] && !cpsr[`CPSR_Z];
		`COND_LS:	condition_met = !cpsr[`CPSR_C] || cpsr[`CPSR_Z];
		`COND_GE:	condition_met = cpsr[`CPSR_N] == cpsr[`CPSR_V];
		`COND_LT:	condition_met = cpsr[`CPSR_N] != cpsr[`CPSR_V];
		`COND_GT:	condition_met = !cpsr[`CPSR_Z] && (cpsr[`CPSR_N] == cpsr[`CPSR_V]);
		`COND_LE:	condition_met = cpsr[`CPSR_Z] || (cpsr[`CPSR_N] != cpsr[`CPSR_V]);
		`COND_AL:	condition_met = 1;
		`COND_NV:	condition_met = 0;
		default:	condition_met = 1'bx;
		endcase
	
	/* Issue logic */
`define STAGE_EXECUTE   0
`define STAGE_MEMORY    1
/* Once it's hit writeback, it's essentially hit the regfile so you're done. */
	reg cpsr_inflight [1:0];
	reg [15:0] regs_inflight [1:0];
	
	reg waiting_cpsr;
	reg waiting_regs;
	wire waiting = waiting_cpsr | waiting_regs;
	
	initial
	begin
		cpsr_inflight[0] = 0;
		cpsr_inflight[1] = 0;
		regs_inflight[0] = 0;
		regs_inflight[1] = 0;
	end
		
	always @(*)
	begin
		waiting_cpsr = use_cpsr & (cpsr_inflight[0] | cpsr_inflight[1]);
		waiting_regs = |(use_regs & (regs_inflight[0] | regs_inflight[1]));
	end
	
	/* Actually do the issue. */
	always @(posedge clk)
	begin
		cpsr_inflight[0] <= cpsr_inflight[1];	/* I'm not sure how well selects work with arrays, and that seems like a dumb thing to get anusulated by. */
		cpsr_inflight[1] <= ((waiting | inbubble) && condition_met) ? 0 : def_cpsr;
		regs_inflight[0] <= regs_inflight[1];
		regs_inflight[1] <= ((waiting | inbubble) && condition_met) ? 0 : def_regs;

		outbubble <= inbubble | waiting | !condition_met;
		outpc <= inpc;
		outinsn <= insn;
		outstall <= waiting && !inbubble;
	end
endmodule
Commit	Line	Data
7aa8541b JW	1	`include "ARM_Constants.v"
7aa8541b JW	2
60cc768b JW	3	module Issue(
60cc768b JW	4	input clk,
09e28f01	5	input Nrst, /* XXX not used yet */
60cc768b JW	6
	7	input stall, /* pipeline control */
	8	input flush,
	9
	10	input inbubble, /* stage inputs */
	11	input [31:0] insn,
	12	input [31:0] inpc,
ae281afd	13	input [31:0] cpsr,
60cc768b	14
6595c4c8 JW	15	output reg outstall, /* stage outputs */
	16	output reg outbubble,
	17	output reg [31:0] outpc,
	18	output reg [31:0] outinsn
	19	/* XXX other? */
60cc768b JW	20	);
60cc768b JW	21
6595c4c8	22
60cc768b JW	23
	24	`ifdef COPY_PASTA_FODDER
	25	/* from page 2 of ARM7TDMIvE2.pdf */
	26	casex (insn)
	27	32'b????000000??????????????1001????: /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
e216a134 JW	28	// 32'b????00001???????????????1001????: /* Multiply long */
	29	32'b????00010?001111????000000000000: /* MRS (Transfer PSR to register) */
	30	32'b????00010?101001111100000000????: /* MSR (Transfer register to PSR) */
	31	32'b????00?10?1010001111????????????: /* MSR (Transfer register or immediate to PSR, flag bits only) */
60cc768b JW	32	32'b????00??????????????????????????: /* ALU */
	33	32'b????00010?00????????00001001????: /* Atomic swap */
	34	32'b????000100101111111111110001????: /* Branch */
	35	32'b????000??0??????????00001??1????: /* Halfword transfer - register offset */
	36	32'b????000??1??????????00001??1????: /* Halfword transfer - register offset */
	37	32'b????011????????????????????1????: /* Undefined. I hate ARM */
	38	32'b????01??????????????????????????: /* Single data transfer */
	39	32'b????100?????????????????????????: /* Block data transfer */
	40	32'b????101?????????????????????????: /* Branch */
	41	32'b????110?????????????????????????: /* Coprocessor data transfer */
	42	32'b????1110???????????????????0????: /* Coprocessor data op */
	43	32'b????1110???????????????????1????: /* Coprocessor register transfer */
	44	32'b????1111????????????????????????: /* SWI */
e216a134	45	default: /* X everything else out */
60cc768b JW	46	endcase
	47	`endif
	48
e216a134 JW	49	/* Flag setting */
	50	reg use_cpsr;
	51	reg [15:0] use_regs;
	52	reg def_cpsr;
	53	reg [15:0] def_regs;
	54
	55	function [15:0] idxbit;
	56	input [3:0] r;
7aa8541b JW	57	if (r == 15)
	58	idxbit = 0;
	59	else
	60	idxbit = (16'b1) << r;
e216a134 JW	61	endfunction
	62
	63	wire [3:0] rn = insn[19:16];
	64	wire [3:0] rd = insn[15:12];
7aa8541b	65	wire [3:0] rs = insn[11:8];
e216a134 JW	66	wire [3:0] rm = insn[3:0];
	67	wire [3:0] cond = insn[31:28];
	68
	69	wire [3:0] rd_mul = insn[19:16];
	70	wire [3:0] rn_mul = insn[15:12];
	71	wire [3:0] rs_mul = insn[11:8];
	72
7aa8541b JW	73	wire [3:0] alu_opc = insn[24:21];
	74
	75	function alu_is_logical;
	76	input [3:0] op;
	77
	78	case (op)
	79	`ALU_AND,`ALU_EOR,`ALU_TST,`ALU_TEQ,`ALU_ORR,`ALU_MOV,`ALU_BIC,`ALU_MVN: alu_is_logical = 1;
	80	default: alu_is_logical = 0;
	81	endcase
	82	endfunction
	83
	84	function alu_flags_only;
	85	input [3:0] op;
	86
	87	case (op)
	88	`ALU_TST,`ALU_TEQ,`ALU_CMP,`ALU_CMN: alu_flags_only = 1;
	89	default: alu_flags_only = 0;
	90	endcase
	91	endfunction
	92
	93	function shift_requires_carry;
	94	input [7:0] shift;
	95
	96	case(shift[1:0])
	97	`SHIFT_LSL: shift_requires_carry = (shift[7:2] == 0);
	98	`SHIFT_LSR: shift_requires_carry = 0;
	99	`SHIFT_ASR: shift_requires_carry = 0;
	100	`SHIFT_ROR: shift_requires_carry = (shift[7:2] == 0);
	101	endcase
	102	endfunction
	103
e216a134	104	always @(*)
7aa8541b	105	casez (insn)
e216a134 JW	106	32'b????000000??????????????1001????: /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
	107	begin
	108	use_cpsr = `COND_MATTERS(cond);
	109	use_regs = (insn[21] /* accum */ ? idxbit(rn_mul) : 0) \| idxbit(rs_mul) \| idxbit(rm);
	110	def_cpsr = insn[20] /* setcc */;
	111	def_regs = idxbit(rd_mul);
	112	end
	113	// 32'b????00001???????????????1001????: /* Multiply long */
	114	32'b????00010?001111????000000000000: /* MRS (Transfer PSR to register) */
7aa8541b JW	115	begin
	116	use_cpsr = `COND_MATTERS(cond) \|\| (insn[22] == 0) /* Source = CPSR */;
	117	use_regs = 0;
	118	def_cpsr = 0;
	119	def_regs = idxbit(rd);
	120	end
e216a134	121	32'b????00010?101001111100000000????: /* MSR (Transfer register to PSR) */
7aa8541b JW	122	begin
	123	use_cpsr = `COND_MATTERS(cond);
	124	use_regs = idxbit(rm);
	125	def_cpsr = 1;
	126	def_regs = 0;
	127	end
e216a134	128	32'b????00?10?1010001111????????????: /* MSR (Transfer register or immediate to PSR, flag bits only) */
7aa8541b JW	129	begin
	130	use_cpsr = `COND_MATTERS(cond);
	131	use_regs = insn[25] ? 0 : idxbit(rm);
	132	def_cpsr = 1;
	133	def_regs = 0;
	134	end
e216a134	135	32'b????00??????????????????????????: /* ALU */
7aa8541b JW	136	begin
	137	use_cpsr = `COND_MATTERS(cond) \| (!insn[25] /* I */ && shift_requires_carry(insn[11:4]));
	138	use_regs =
	139	(insn[25] /* I */ ? 0 :
	140	(insn[4] /* shift by reg */ ?
	141	(idxbit(rs) \| idxbit(rm)) :
	142	(idxbit(rm)))) \|
	143	(((alu_opc != `ALU_MOV) && (alu_opc != `ALU_MVN)) ? idxbit(rn) : 0);
	144	def_cpsr = insn[20] /* S */ \| alu_is_logical(alu_opc);
	145	def_regs = alu_flags_only(alu_opc) ? 0 : idxbit(rd);
	146	end
e216a134	147	32'b????00010?00????????00001001????: /* Atomic swap */
7aa8541b JW	148	begin
	149	use_cpsr = `COND_MATTERS(cond);
	150	use_regs = idxbit(rn) \| idxbit(rm);
	151	def_cpsr = 0;
	152	def_regs = idxbit(rd);
	153	end
e216a134	154	32'b????000100101111111111110001????: /* Branch */
7aa8541b JW	155	begin
	156	use_cpsr = `COND_MATTERS(cond);
	157	use_regs = idxbit(rm);
	158	def_cpsr = 0; // don't care, we'll never get there
	159	def_regs = 0;
	160	end
e216a134	161	32'b????000??0??????????00001??1????: /* Halfword transfer - register offset */
7aa8541b JW	162	begin
	163	use_cpsr = `COND_MATTERS(cond);
	164	use_regs = idxbit(rn) \| idxbit(rm) \| (insn[20] /* L */ ? 0 : idxbit(rd));
	165	def_cpsr = 0;
	166	def_regs = insn[20] /* L */ ? idxbit(rd) : 0;
	167	end
	168	32'b????000??1??????????00001??1????: /* Halfword transfer - immediate offset */
	169	begin
	170	use_cpsr = `COND_MATTERS(cond);
	171	use_regs = idxbit(rn) \| (insn[20] /* L */ ? 0 : idxbit(rd));
	172	def_cpsr = 0;
	173	def_regs = insn[20] /* L */ ? idxbit(rd) : 0;
	174	end
e216a134	175	32'b????011????????????????????1????: /* Undefined. I hate ARM */
7aa8541b JW	176	begin
	177	use_cpsr = 0;
	178	use_regs = 0;
	179	def_cpsr = 0;
	180	def_regs = 0;
	181	end
e216a134	182	32'b????100?????????????????????????: /* Block data transfer */
7aa8541b JW	183	begin
	184	use_cpsr = `COND_MATTERS(cond);
	185	use_regs = idxbit(rn) \| (insn[20] /* L */ ? 0 : insn[15:0]);
	186	def_cpsr = insn[22]; /* This is a superset of all cases, anyway. */
	187	def_regs = (insn[21] /* W / ? idxbit(rn) : 0) \| (insn[20] / L */ ? insn[15:0] : 0);
	188	end
e216a134	189	32'b????101?????????????????????????: /* Branch */
7aa8541b JW	190	begin
	191	use_cpsr = `COND_MATTERS(cond);
	192	use_regs = 0;
	193	def_cpsr = 0;
	194	def_regs = 0;
	195	end
e216a134	196	32'b????110?????????????????????????: /* Coprocessor data transfer */
7aa8541b JW	197	begin
	198	use_cpsr = `COND_MATTERS(cond);
	199	use_regs = idxbit(rn);
	200	def_cpsr = 0;
	201	def_regs = insn[21] /* W */ ? idxbit(rn) : 0;
	202	end
e216a134	203	32'b????1110???????????????????0????: /* Coprocessor data op */
7aa8541b JW	204	begin
	205	use_cpsr = `COND_MATTERS(cond);
	206	use_regs = 0;
	207	def_cpsr = 0;
	208	def_regs = 0;
	209	end
e216a134	210	32'b????1110???????????????????1????: /* Coprocessor register transfer */
7aa8541b JW	211	begin
	212	use_cpsr = `COND_MATTERS(cond);
	213	use_regs = insn[20] /* L */ ? 0 : idxbit(rd);
	214	def_cpsr = 0;
	215	def_regs = insn[20] /* L */ ? idxbit(rd) : 0;
	216	end
e216a134	217	32'b????1111????????????????????????: /* SWI */
7aa8541b JW	218	begin
	219	use_cpsr = `COND_MATTERS(cond);
	220	use_regs = 0;
	221	def_cpsr = 0;
	222	def_regs = 0;
	223	end
e216a134	224	default: /* X everything else out */
7aa8541b JW	225	begin
	226	use_cpsr = 1'bx;
	227	use_regs = 16'bxxxxxxxxxxxxxxxx;
	228	def_cpsr = 1'bx;
	229	def_regs = 16'bxxxxxxxxxxxxxxxx;
	230	end
e216a134	231	endcase
ae281afd JW	232
	233	/* Condition checking logic */
	234	reg condition_met;
	235	always @(*)
	236	casez(insn[31:28])
	237	`COND_EQ: condition_met = cpsr[`CPSR_Z];
	238	`COND_NE: condition_met = !cpsr[`CPSR_Z];
	239	`COND_CS: condition_met = cpsr[`CPSR_C];
	240	`COND_CC: condition_met = !cpsr[`CPSR_C];
	241	`COND_MI: condition_met = cpsr[`CPSR_N];
	242	`COND_PL: condition_met = !cpsr[`CPSR_N];
	243	`COND_VS: condition_met = cpsr[`CPSR_V];
	244	`COND_VC: condition_met = !cpsr[`CPSR_V];
	245	`COND_HI: condition_met = cpsr[`CPSR_C] && !cpsr[`CPSR_Z];
	246	`COND_LS: condition_met = !cpsr[`CPSR_C] \|\| cpsr[`CPSR_Z];
	247	`COND_GE: condition_met = cpsr[`CPSR_N] == cpsr[`CPSR_V];
	248	`COND_LT: condition_met = cpsr[`CPSR_N] != cpsr[`CPSR_V];
	249	`COND_GT: condition_met = !cpsr[`CPSR_Z] && (cpsr[`CPSR_N] == cpsr[`CPSR_V]);
	250	`COND_LE: condition_met = cpsr[`CPSR_Z] \|\| (cpsr[`CPSR_N] != cpsr[`CPSR_V]);
	251	`COND_AL: condition_met = 1;
	252	`COND_NV: condition_met = 0;
	253	default: condition_met = 1'bx;
	254	endcase
	255
	256	/* Issue logic */
6595c4c8 JW	257	`define STAGE_EXECUTE 0
	258	`define STAGE_MEMORY 1
	259	/* Once it's hit writeback, it's essentially hit the regfile so you're done. */
	260	reg cpsr_inflight [1:0];
	261	reg [15:0] regs_inflight [1:0];
	262
	263	reg waiting_cpsr;
	264	reg waiting_regs;
	265	wire waiting = waiting_cpsr \| waiting_regs;
	266
3ae4e7db JW	267	initial
	268	begin
	269	cpsr_inflight[0] = 0;
	270	cpsr_inflight[1] = 0;
	271	regs_inflight[0] = 0;
	272	regs_inflight[1] = 0;
	273	end
	274
6595c4c8 JW	275	always @(*)
	276	begin
	277	waiting_cpsr = use_cpsr & (cpsr_inflight[0] \| cpsr_inflight[1]);
	278	waiting_regs = \|(use_regs & (regs_inflight[0] \| regs_inflight[1]));
	279	end
	280
	281	/* Actually do the issue. */
6595c4c8 JW	282	always @(posedge clk)
	283	begin
	284	cpsr_inflight[0] <= cpsr_inflight[1]; /* I'm not sure how well selects work with arrays, and that seems like a dumb thing to get anusulated by. */
09e28f01	285	cpsr_inflight[1] <= ((waiting \| inbubble) && condition_met) ? 0 : def_cpsr;
6595c4c8	286	regs_inflight[0] <= regs_inflight[1];
09e28f01	287	regs_inflight[1] <= ((waiting \| inbubble) && condition_met) ? 0 : def_regs;
6595c4c8 JW	288
	289	outbubble <= inbubble \| waiting \| !condition_met;
	290	outpc <= inpc;
	291	outinsn <= insn;
a221c031	292	outstall <= waiting && !inbubble;
6595c4c8	293	end
60cc768b	294	endmodule