Execute: Fix carry flag on subtraction operations.

[firearm.git] / Execute.v

diff --git a/Execute.v b/Execute.v
index e00e93d240e13ea87256b601768673fb2bf8117c..ac446aafffc6d88fb73554b61716e2433717527b 100644 (file)
--- a/Execute.v
+++ b/Execute.v
@@ -9,15 +9,204 @@ module Execute(
        input [31:0] pc,
        input [31:0] insn,
        input [31:0] cpsr,
        input [31:0] pc,
        input [31:0] insn,
        input [31:0] cpsr,

+       input [31:0] spsr,

        input [31:0] op0,
        input [31:0] op1,
        input [31:0] op2,
        input carry,
        
        output reg outstall = 0,
        input [31:0] op0,
        input [31:0] op1,
        input [31:0] op2,
        input carry,
        
        output reg outstall = 0,

-       output reg outbubble = 1
+       output reg outbubble = 1,
+       output reg [31:0] outcpsr = 0,
+       output reg [31:0] outspsr = 0,
+       output reg outcpsrup = 0,
+       output reg write_reg = 1'bx,
+       output reg [3:0] write_num = 4'bxxxx,
+       output reg [31:0] write_data = 32'hxxxxxxxx,
+       output reg [31:0] jmppc,
+       output reg jmp,
+       output reg [31:0] outpc,
+       output reg [31:0] outinsn,
+       output reg [31:0] outop0, outop1, outop2

        );
        
        );
        

+       reg mult_start;
+       reg [31:0] mult_acc0, mult_in0, mult_in1;
+       wire mult_done;
+       wire [31:0] mult_result;
+       
+       reg [31:0] alu_in0, alu_in1;
+       reg [3:0] alu_op;
+       reg alu_setflags;
+       wire [31:0] alu_result, alu_outcpsr;
+       wire alu_setres;
+       
+       reg next_outbubble;
+       reg [31:0] next_outcpsr, next_outspsr;
+       reg next_outcpsrup;
+       reg next_write_reg;
+       reg [3:0] next_write_num;
+
+       reg [31:0] next_write_data;
+
+       Multiplier multiplier(
+               .clk(clk), .Nrst(Nrst),
+               .start(mult_start), .acc0(mult_acc0), .in0(mult_in0),
+               .in1(mult_in1), .done(mult_done), .result(mult_result));
+       
+       ALU alu(
+               .clk(clk), .Nrst(Nrst),
+               .in0(alu_in0), .in1(alu_in1), .cpsr(cpsr), .op(alu_op),
+               .setflags(alu_setflags), .shifter_carry(carry),
+               .result(alu_result), .cpsr_out(alu_outcpsr), .setres(alu_setres));
+
+       always @(posedge clk)
+       begin
+               if (!stall)
+               begin
+                       outbubble <= next_outbubble;
+                       outcpsr <= next_outcpsr;
+                       outspsr <= next_outspsr;
+                       outcpsrup <= next_outcpsrup;
+                       write_reg <= next_write_reg;
+                       write_num <= next_write_num;
+                       write_data <= next_write_data;
+                       outpc <= pc;
+                       outinsn <= insn;
+                       outop0 <= op0;
+                       outop1 <= op1;
+                       outop2 <= op2;
+               end
+       end
+       
+       reg delayedflush = 0;
+       always @(posedge clk)
+               if (flush && outstall /* halp! I can't do it now, maybe later? */)
+                       delayedflush <= 1;
+               else if (!outstall /* anything has been handled this time around */)
+                       delayedflush <= 0;
+
+       reg prevstall = 0;
+       always @(posedge clk)
+               prevstall <= outstall;
+
+       always @(*)
+       begin
+               outstall = stall;
+               next_outbubble = inbubble | flush | delayedflush;
+               next_outcpsr = cpsr;
+               next_outspsr = spsr;
+               next_outcpsrup = 0;
+               next_write_reg = 0;
+               next_write_num = 4'hx;
+               next_write_data = 32'hxxxxxxxx;
+
+               mult_start = 0;
+               mult_acc0 = 32'hxxxxxxxx;
+               mult_in0 = 32'hxxxxxxxx;
+               mult_in1 = 32'hxxxxxxxx;
+
+               alu_in0 = 32'hxxxxxxxx;
+               alu_in1 = 32'hxxxxxxxx;
+               alu_op = 4'hx;  /* hax! */
+               alu_setflags = 1'bx;
+
+               jmp = 1'b0;
+               jmppc = 32'h00000000;
+
+               casez (insn)
+               `DECODE_ALU_MULT:       /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
+               begin
+                       if (!prevstall && !inbubble)
+                       begin
+                               mult_start = 1;
+                               mult_acc0 = insn[21] /* A */ ? op0 /* Rn */ : 32'h0;
+                               mult_in0 = op1 /* Rm */;
+                               mult_in1 = op2 /* Rs */;
+                               $display("New MUL instruction");
+                       end
+                       outstall = outstall | ((!prevstall | !mult_done) && !inbubble);
+                       next_outbubble = next_outbubble | !mult_done | !prevstall;
+                       next_outcpsr = insn[20] /* S */ ? {mult_result[31] /* N */, mult_result == 0 /* Z */, 1'b0 /* C */, cpsr[28] /* V */, cpsr[27:0]} : cpsr;
+                       next_outcpsrup = insn[20] /* S */;
+                       next_write_reg = 1;
+                       next_write_num = insn[19:16] /* Rd -- why the fuck isn't this the same place as ALU */;
+                       next_write_data = mult_result;
+               end
+//             `DECODE_ALU_MUL_LONG,   /* Multiply long */
+               `DECODE_ALU_MRS:        /* MRS (Transfer PSR to register) */
+               begin
+                       next_write_reg = 1;
+                       next_write_num = insn[15:12];
+                       if (insn[22] /* Ps */)
+                               next_write_data = spsr;
+                       else
+                               next_write_data = cpsr;
+                       next_outcpsrup = 1;
+               end
+               `DECODE_ALU_MSR,        /* MSR (Transfer register to PSR) */
+               `DECODE_ALU_MSR_FLAGS:  /* MSR (Transfer register or immediate to PSR, flag bits only) */
+               begin
+                       if ((cpsr[4:0] == `MODE_USR) || (insn[16] /* that random bit */ == 1'b0))       /* flags only */
+                       begin
+                               if (insn[22] /* Ps */)
+                                       next_outspsr = {op0[31:29], spsr[28:0]};
+                               else
+                                       next_outcpsr = {op0[31:29], cpsr[28:0]};
+                       end else begin
+                               if (insn[22] /* Ps */)
+                                       next_outspsr = op0;
+                               else
+                                       next_outcpsr = op0;
+                       end
+                       next_outcpsrup = 1;
+               end
+               `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 */
+               begin end
+               `DECODE_ALU:            /* ALU */
+               begin
+                       alu_in0 = op0;
+                       alu_in1 = op1;
+                       alu_op = insn[24:21];
+                       alu_setflags = insn[20] /* S */;
+                       
+                       if (alu_setres) begin
+                               next_write_reg = 1;
+                               next_write_num = insn[15:12] /* Rd */;
+                               next_write_data = alu_result;
+                       end
+                       
+                       next_outcpsr = ((insn[15:12] == 4'b1111) && insn[20]) ? spsr : alu_outcpsr;
+                       next_outcpsrup = insn[20] /* S */;
+               end
+               `DECODE_LDRSTR_UNDEFINED,       /* Undefined. I hate ARM */
+               `DECODE_LDRSTR,         /* Single data transfer */
+               `DECODE_LDMSTM:         /* Block data transfer */
+               begin end
+               `DECODE_BRANCH:
+               begin
+                       if(!inbubble && !flush && !delayedflush && !outstall /* Let someone else take precedence. */) begin
+                               jmppc = pc + op0 + 32'h8;
+                               if(insn[24]) begin
+                                       next_write_reg = 1;
+                                       next_write_num = 4'hE; /* link register */
+                                       next_write_data = pc + 32'h4;
+                               end
+                               jmp = 1'b1;
+                       end
+               end                     /* Branch */
+               `DECODE_LDCSTC,         /* Coprocessor data transfer */
+               `DECODE_CDP,            /* Coprocessor data op */
+               `DECODE_MRCMCR,         /* Coprocessor register transfer */
+               `DECODE_SWI:            /* SWI */
+               begin end
+               default:                /* X everything else out */
+               begin end
+               endcase
+       end

 endmodule
 
 module Multiplier(
 endmodule
 
 module Multiplier(


@@ -56,3 +245,130 @@ module Multiplier(
                end
        end
 endmodule
                end
        end
 endmodule

+
+module ALU(
+       input clk,
+       input Nrst,     /* XXX not used yet */
+
+       input [31:0] in0,
+       input [31:0] in1,
+       input [31:0] cpsr,
+       input [3:0] op,
+       input setflags,
+       input shifter_carry,
+
+       output reg [31:0] result,
+       output reg [31:0] cpsr_out,
+       output reg setres
+);
+       reg [31:0] res;
+       reg flag_n, flag_z, flag_c, flag_v;
+       wire [32:0] sum, diff, rdiff;
+       wire sum_v, diff_v, rdiff_v;
+
+       assign sum = {1'b0, in0} + {1'b0, in1};
+       assign diff = {1'b0, in0} - {1'b0, in1};
+       assign rdiff = {1'b0, in1} - {1'b0, in0};
+       assign sum_v = (in0[31] ^~ in1[31]) & (sum[31] ^ in0[31]);
+       assign diff_v = (in0[31] ^ in1[31]) & (diff[31] ^ in0[31]);
+       assign rdiff_v = (in0[31] ^ in1[31]) & (rdiff[31] ^ in1[31]);
+
+       always @(*) begin
+               res = 32'hxxxxxxxx;
+               setres = 1'bx;
+               flag_c = cpsr[`CPSR_C];
+               flag_v = cpsr[`CPSR_V];
+               case(op)
+               `ALU_AND: begin
+                       result = in0 & in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b1;
+               end
+               `ALU_EOR: begin
+                       result = in0 ^ in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b1;
+               end
+               `ALU_SUB: begin
+                       {flag_c, result} = diff;
+                       flag_c = !flag_c;
+                       flag_v = diff_v;
+                       setres = 1'b1;
+               end
+               `ALU_RSB: begin
+                       {flag_c, result} = rdiff;
+                       flag_c = !flag_c;
+                       flag_v = rdiff_v;
+                       setres = 1'b1;
+               end
+               `ALU_ADD: begin
+                       {flag_c, result} = sum;
+                       flag_v = sum_v;
+                       setres = 1'b1;
+               end
+               `ALU_ADC: begin
+                       {flag_c, result} = sum + {32'b0, cpsr[`CPSR_C]};
+                       flag_v = sum_v | (~sum[31] & result[31]);
+                       setres = 1'b1;
+               end
+               `ALU_SBC: begin
+                       {flag_c, result} = diff - {32'b0, (~cpsr[`CPSR_C])};
+                       flag_c = !flag_c;
+                       flag_v = diff_v | (diff[31] & ~result[31]);
+                       setres = 1'b1;
+               end
+               `ALU_RSC: begin
+                       {flag_c, result} = rdiff - {32'b0, (~cpsr[`CPSR_C])};
+                       flag_c = !flag_c;
+                       flag_v = rdiff_v | (rdiff[31] & ~result[31]);
+                       setres = 1'b1;
+               end
+               `ALU_TST: begin
+                       result = in0 & in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b0;
+               end
+               `ALU_TEQ: begin
+                       result = in0 ^ in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b0;
+               end
+               `ALU_CMP: begin
+                       {flag_c, result} = diff;
+                       flag_c = !flag_c;
+                       flag_v = diff_v;
+                       setres = 1'b0;
+               end
+               `ALU_CMN: begin
+                       {flag_c, result} = sum;
+                       flag_v = sum_v;
+                       setres = 1'b0;
+               end
+               `ALU_ORR: begin
+                       result = in0 | in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b1;
+               end
+               `ALU_MOV: begin
+                       result = in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b1;
+               end
+               `ALU_BIC: begin
+                       result = in0 & (~in1);
+                       flag_c = shifter_carry;
+                       setres = 1'b1;
+               end
+               `ALU_MVN: begin
+                       result = ~in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b1;
+               end
+               endcase
+               
+               flag_z = (result == 0);
+               flag_n = result[31];
+               
+               cpsr_out = setflags ? {flag_n, flag_z, flag_c, flag_v, cpsr[27:0]} : cpsr;
+       end
+endmodule