Decode: Fix stupid bug in which stalls did not stall the decoder.
[firearm.git] / Issue.v
diff --git a/Issue.v b/Issue.v
index a303e85..7b281a3 100644 (file)
--- a/Issue.v
+++ b/Issue.v
+`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 */
        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????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 */
+       `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
 
+       /* 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)
+               `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
+//             `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
+               `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
+               `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
+               `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
+               `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
+               `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
+               `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
+               `DECODE_ALU:    /* 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 */;
+                       def_regs = alu_flags_only(alu_opc) ? 0 : idxbit(rd);
+               end
+               `DECODE_LDRSTR_UNDEFINED:       /* Undefined. I hate ARM */
+               begin   
+                       use_cpsr = 0;
+                       use_regs = 0;
+                       def_cpsr = 0;
+                       def_regs = 0;
+               end
+               `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
+               `DECODE_BRANCH: /* Branch */
+               begin
+                       use_cpsr = `COND_MATTERS(cond);
+                       use_regs = 0;
+                       def_cpsr = 0;
+                       def_regs = 0;
+               end
+               `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
+               `DECODE_CDP:    /* Coprocessor data op */
+               begin
+                       use_cpsr = `COND_MATTERS(cond);
+                       use_regs = 0;
+                       def_cpsr = 0;
+                       def_regs = 0;
+               end
+               `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
+               `DECODE_SWI:    /* 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]));
+               
+               outstall = ((waiting && !inbubble) || stall) && !flush; /* Happens in an always @*, because it is an exception. */
+       end
+       
+       /* Actually do the issue. */
+       always @(posedge clk)
+       begin
+               if (waiting)
+                       $display("ISSUE: Stalling instruction %08x because %d/%d", insn, waiting_cpsr, waiting_regs);
+
+               if(flush)
+               begin
+                       cpsr_inflight[0] = 1'b0;
+                       cpsr_inflight[1] = 1'b0;
+                       regs_inflight[0] = 16'b0;
+                       regs_inflight[1] = 16'b0;
+                       outbubble <= 1'b1;
+               end
+               else if (!stall)
+               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;
+               end
+       end
 endmodule
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