Execute: Fix carry flag on subtraction operations.
[firearm.git] / Execute.v
index 66a63e5..ac446aa 100644 (file)
--- a/Execute.v
+++ b/Execute.v
@@ -19,6 +19,7 @@ module Execute(
        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,
@@ -42,6 +43,7 @@ module Execute(
        
        reg next_outbubble;
        reg [31:0] next_outcpsr, next_outspsr;
+       reg next_outcpsrup;
        reg next_write_reg;
        reg [3:0] next_write_num;
 
@@ -65,6 +67,7 @@ module Execute(
                        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;
@@ -93,6 +96,7 @@ module Execute(
                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;
@@ -121,9 +125,10 @@ module Execute(
                                mult_in1 = op2 /* Rs */;
                                $display("New MUL instruction");
                        end
-                       outstall = stall | ((!prevstall | !mult_done) && !inbubble);
-                       next_outbubble = inbubble | !mult_done | !prevstall;
+                       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;
@@ -137,9 +142,11 @@ module Execute(
                                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 */)
@@ -152,6 +159,8 @@ module Execute(
                                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 */
@@ -171,6 +180,7 @@ module Execute(
                        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 */
@@ -178,7 +188,7 @@ module Execute(
                begin end
                `DECODE_BRANCH:
                begin
-                       if(!inbubble && !flush && !delayedflush) 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;
@@ -258,7 +268,7 @@ module ALU(
 
        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 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]);
@@ -281,11 +291,13 @@ module ALU(
                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
@@ -301,11 +313,13 @@ module ALU(
                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
@@ -321,6 +335,7 @@ module ALU(
                end
                `ALU_CMP: begin
                        {flag_c, result} = diff;
+                       flag_c = !flag_c;
                        flag_v = diff_v;
                        setres = 1'b0;
                end
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