+`include "ARM_Constants.v"
+
module Issue(
input clk,
- input Nrst,
+ input Nrst, /* XXX not used yet */
input stall, /* pipeline control */
- input flush,
+ input flush, /* XXX not used yet */
input inbubble, /* stage inputs */
input [31:0] insn,
input [31:0] inpc,
+ input [31:0] cpsr,
- output reg outbubble, /* stage outputs */
- output reg [31:0] outpc
- /* other */
+ output reg outstall = 0, /* stage outputs */
+ output reg outbubble = 1,
+ output reg [31:0] outpc = 0,
+ output reg [31:0] outinsn = 0
+ /* XXX other? */
);
- always @(posedge clk)
- begin
- outbubble <= inbubble;
- outpc <= inpc;
- end
+
`ifdef COPY_PASTA_FODDER
/* from page 2 of ARM7TDMIvE2.pdf */
endcase
`endif
-`ifdef WIP
/* Flag setting */
reg use_cpsr;
reg [15:0] use_regs;
function [15:0] idxbit;
input [3:0] r;
- idxbit = (16'b1) << 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] 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 @(*)
- casex (insn)
+ 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);
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 */
- 32'b????000??1??????????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 */
- 32'b????01??????????????????????????: /* Single data transfer */
+ 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
-`endif
+
+ /* 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]));
+
+ outstall = waiting && !inbubble; /* Happens in an always @*, because it is an exception. */
+ 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;
+
+ if (waiting)
+ begin
+ $display("ISSUE: Stalling instruction %08x because %d/%d", insn, waiting_cpsr, waiting_regs);
+ end
+
+ outbubble <= inbubble | waiting | !condition_met;
+ outpc <= inpc;
+ outinsn <= insn;
+ end
endmodule
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