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 */
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 */
+ `DECODE_ALU_MULT: /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
+// `DECODE_ALU_MUL_LONG: /* Multiply long */
+ `DECODE_ALU_MRS: /* MRS (Transfer PSR to register) */
+ `DECODE_ALU_MSR: /* MSR (Transfer register to PSR) */
+ `DECODE_ALU_MSR_FLAGS: /* MSR (Transfer register or immediate to PSR, flag bits only) */
+ `DECODE_ALU_SWP: /* Atomic swap */
+ `DECODE_ALU_BX: /* Branch */
+ `DECODE_ALU_HDATA_REG: /* Halfword transfer - register offset */
+ `DECODE_ALU_HDATA_IMM: /* Halfword transfer - immediate offset */
+ `DECODE_ALU: /* ALU */
+ `DECODE_LDRSTR_UNDEFINED: /* Undefined. I hate ARM */
+ `DECODE_LDRSTR: /* Single data transfer */
+ `DECODE_LDMSTM: /* Block data transfer */
+ `DECODE_BRANCH: /* Branch */
+ `DECODE_LDCSTC: /* Coprocessor data transfer */
+ `DECODE_CDP: /* Coprocessor data op */
+ `DECODE_MRCMCR: /* Coprocessor register transfer */
+ `DECODE_SWI: /* SWI */
+ default: /* X everything else out */
endcase
`endif
always @(*)
casez (insn)
- 32'b????000000??????????????1001????: /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
+ `DECODE_ALU_MULT: /* 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) */
+// `DECODE_ALU_MUL_LONG: /* Multiply long */
+ `DECODE_ALU_MRS: /* 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) */
+ `DECODE_ALU_MSR: /* 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) */
+ `DECODE_ALU_MSR_FLAGS: /* 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 */
+ `DECODE_ALU: /* ALU */
begin
use_cpsr = `COND_MATTERS(cond) | (!insn[25] /* I */ && shift_requires_carry(insn[11:4]));
use_regs =
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 */
+ `DECODE_ALU_SWP: /* 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 */
+ `DECODE_ALU_BX: /* 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 */
+ `DECODE_ALU_HDATA_REG: /* 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 */
+ `DECODE_ALU_HDATA_IMM: /* 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 */
+ `DECODE_LDRSTR_UNDEFINED: /* Undefined. I hate ARM */
begin
use_cpsr = 0;
use_regs = 0;
def_cpsr = 0;
def_regs = 0;
end
- 32'b????100?????????????????????????: /* Block data transfer */
+ `DECODE_LDRSTR:
+ 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
+ `DECODE_LDMSTM: /* 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 */
+ `DECODE_BRANCH: /* Branch */
begin
use_cpsr = `COND_MATTERS(cond);
use_regs = 0;
def_cpsr = 0;
def_regs = 0;
end
- 32'b????110?????????????????????????: /* Coprocessor data transfer */
+ `DECODE_LDCSTC: /* 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 */
+ `DECODE_CDP: /* 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 */
+ `DECODE_MRCMCR: /* 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 */
+ `DECODE_SWI: /* SWI */
begin
use_cpsr = `COND_MATTERS(cond);
use_regs = 0;
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]));
+
+ 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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