Execute: Fix carry flag on subtraction operations.
[firearm.git] / Execute.v
CommitLineData
5b3daee2
JW
1module Execute(
2 input clk,
3 input Nrst, /* XXX not used yet */
4
5 input stall,
6 input flush,
7
8 input inbubble,
9 input [31:0] pc,
10 input [31:0] insn,
11 input [31:0] cpsr,
cb0428b6 12 input [31:0] spsr,
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JW
13 input [31:0] op0,
14 input [31:0] op1,
15 input [31:0] op2,
16 input carry,
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JW
17
18 output reg outstall = 0,
bc572c5f 19 output reg outbubble = 1,
6e3dfd79 20 output reg [31:0] outcpsr = 0,
cb0428b6 21 output reg [31:0] outspsr = 0,
fdecc897 22 output reg outcpsrup = 0,
bc572c5f
JW
23 output reg write_reg = 1'bx,
24 output reg [3:0] write_num = 4'bxxxx,
314dac21 25 output reg [31:0] write_data = 32'hxxxxxxxx,
149bcd1a 26 output reg [31:0] jmppc,
2393422a
JW
27 output reg jmp,
28 output reg [31:0] outpc,
c65110a8
JW
29 output reg [31:0] outinsn,
30 output reg [31:0] outop0, outop1, outop2
5b3daee2 31 );
5b3daee2 32
bc572c5f
JW
33 reg mult_start;
34 reg [31:0] mult_acc0, mult_in0, mult_in1;
35 wire mult_done;
36 wire [31:0] mult_result;
37
2b091cd4
JW
38 reg [31:0] alu_in0, alu_in1;
39 reg [3:0] alu_op;
40 reg alu_setflags;
6e3dfd79 41 wire [31:0] alu_result, alu_outcpsr;
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JW
42 wire alu_setres;
43
44 reg next_outbubble;
cb0428b6 45 reg [31:0] next_outcpsr, next_outspsr;
fdecc897 46 reg next_outcpsrup;
732b7730
JW
47 reg next_write_reg;
48 reg [3:0] next_write_num;
149bcd1a 49
732b7730 50 reg [31:0] next_write_data;
149bcd1a 51
bc572c5f
JW
52 Multiplier multiplier(
53 .clk(clk), .Nrst(Nrst),
54 .start(mult_start), .acc0(mult_acc0), .in0(mult_in0),
55 .in1(mult_in1), .done(mult_done), .result(mult_result));
6e3dfd79
JW
56
57 ALU alu(
58 .clk(clk), .Nrst(Nrst),
59 .in0(alu_in0), .in1(alu_in1), .cpsr(cpsr), .op(alu_op),
60 .setflags(alu_setflags), .shifter_carry(carry),
732b7730 61 .result(alu_result), .cpsr_out(alu_outcpsr), .setres(alu_setres));
b770ec9a 62
732b7730
JW
63 always @(posedge clk)
64 begin
65 if (!stall)
66 begin
67 outbubble <= next_outbubble;
68 outcpsr <= next_outcpsr;
cb0428b6 69 outspsr <= next_outspsr;
fdecc897 70 outcpsrup <= next_outcpsrup;
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JW
71 write_reg <= next_write_reg;
72 write_num <= next_write_num;
73 write_data <= next_write_data;
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JW
74 outpc <= pc;
75 outinsn <= insn;
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JW
76 outop0 <= op0;
77 outop1 <= op1;
78 outop2 <= op2;
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JW
79 end
80 end
b770ec9a
JW
81
82 reg delayedflush = 0;
83 always @(posedge clk)
84 if (flush && outstall /* halp! I can't do it now, maybe later? */)
85 delayedflush <= 1;
86 else if (!outstall /* anything has been handled this time around */)
87 delayedflush <= 0;
2b091cd4 88
af096d96
JW
89 reg prevstall = 0;
90 always @(posedge clk)
91 prevstall <= outstall;
92
2b091cd4 93 always @(*)
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JW
94 begin
95 outstall = stall;
b770ec9a 96 next_outbubble = inbubble | flush | delayedflush;
732b7730 97 next_outcpsr = cpsr;
cb0428b6 98 next_outspsr = spsr;
fdecc897 99 next_outcpsrup = 0;
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JW
100 next_write_reg = 0;
101 next_write_num = 4'hx;
102 next_write_data = 32'hxxxxxxxx;
149bcd1a 103
af096d96
JW
104 mult_start = 0;
105 mult_acc0 = 32'hxxxxxxxx;
106 mult_in0 = 32'hxxxxxxxx;
107 mult_in1 = 32'hxxxxxxxx;
149bcd1a 108
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JW
109 alu_in0 = 32'hxxxxxxxx;
110 alu_in1 = 32'hxxxxxxxx;
111 alu_op = 4'hx; /* hax! */
112 alu_setflags = 1'bx;
149bcd1a
CL
113
114 jmp = 1'b0;
ab7ee9fc 115 jmppc = 32'h00000000;
149bcd1a 116
2b091cd4 117 casez (insn)
af096d96
JW
118 `DECODE_ALU_MULT: /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
119 begin
120 if (!prevstall && !inbubble)
121 begin
122 mult_start = 1;
123 mult_acc0 = insn[21] /* A */ ? op0 /* Rn */ : 32'h0;
124 mult_in0 = op1 /* Rm */;
125 mult_in1 = op2 /* Rs */;
126 $display("New MUL instruction");
127 end
81a01a2b
JW
128 outstall = outstall | ((!prevstall | !mult_done) && !inbubble);
129 next_outbubble = next_outbubble | !mult_done | !prevstall;
af096d96 130 next_outcpsr = insn[20] /* S */ ? {mult_result[31] /* N */, mult_result == 0 /* Z */, 1'b0 /* C */, cpsr[28] /* V */, cpsr[27:0]} : cpsr;
fdecc897 131 next_outcpsrup = insn[20] /* S */;
af096d96
JW
132 next_write_reg = 1;
133 next_write_num = insn[19:16] /* Rd -- why the fuck isn't this the same place as ALU */;
134 next_write_data = mult_result;
135 end
2b091cd4 136// `DECODE_ALU_MUL_LONG, /* Multiply long */
cb0428b6
JW
137 `DECODE_ALU_MRS: /* MRS (Transfer PSR to register) */
138 begin
139 next_write_reg = 1;
140 next_write_num = insn[15:12];
141 if (insn[22] /* Ps */)
142 next_write_data = spsr;
143 else
144 next_write_data = cpsr;
fdecc897 145 next_outcpsrup = 1;
cb0428b6 146 end
2b091cd4 147 `DECODE_ALU_MSR, /* MSR (Transfer register to PSR) */
cb0428b6 148 `DECODE_ALU_MSR_FLAGS: /* MSR (Transfer register or immediate to PSR, flag bits only) */
fdecc897 149 begin
cb0428b6
JW
150 if ((cpsr[4:0] == `MODE_USR) || (insn[16] /* that random bit */ == 1'b0)) /* flags only */
151 begin
152 if (insn[22] /* Ps */)
153 next_outspsr = {op0[31:29], spsr[28:0]};
154 else
155 next_outcpsr = {op0[31:29], cpsr[28:0]};
156 end else begin
157 if (insn[22] /* Ps */)
158 next_outspsr = op0;
159 else
160 next_outcpsr = op0;
161 end
fdecc897
JW
162 next_outcpsrup = 1;
163 end
2b091cd4
JW
164 `DECODE_ALU_SWP, /* Atomic swap */
165 `DECODE_ALU_BX, /* Branch */
166 `DECODE_ALU_HDATA_REG, /* Halfword transfer - register offset */
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JW
167 `DECODE_ALU_HDATA_IMM: /* Halfword transfer - immediate offset */
168 begin end
169 `DECODE_ALU: /* ALU */
170 begin
171 alu_in0 = op0;
172 alu_in1 = op1;
173 alu_op = insn[24:21];
cb0428b6 174 alu_setflags = insn[20] /* S */;
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JW
175
176 if (alu_setres) begin
177 next_write_reg = 1;
178 next_write_num = insn[15:12] /* Rd */;
179 next_write_data = alu_result;
180 end
181
cb0428b6 182 next_outcpsr = ((insn[15:12] == 4'b1111) && insn[20]) ? spsr : alu_outcpsr;
fdecc897 183 next_outcpsrup = insn[20] /* S */;
732b7730 184 end
2b091cd4
JW
185 `DECODE_LDRSTR_UNDEFINED, /* Undefined. I hate ARM */
186 `DECODE_LDRSTR, /* Single data transfer */
314dac21
CL
187 `DECODE_LDMSTM: /* Block data transfer */
188 begin end
189 `DECODE_BRANCH:
190 begin
04281f32 191 if(!inbubble && !flush && !delayedflush && !outstall /* Let someone else take precedence. */) begin
f8bf38ca
CL
192 jmppc = pc + op0 + 32'h8;
193 if(insn[24]) begin
194 next_write_reg = 1;
195 next_write_num = 4'hE; /* link register */
dbf45af6 196 next_write_data = pc + 32'h4;
f8bf38ca
CL
197 end
198 jmp = 1'b1;
314dac21
CL
199 end
200 end /* Branch */
2b091cd4
JW
201 `DECODE_LDCSTC, /* Coprocessor data transfer */
202 `DECODE_CDP, /* Coprocessor data op */
203 `DECODE_MRCMCR, /* Coprocessor register transfer */
204 `DECODE_SWI: /* SWI */
205 begin end
206 default: /* X everything else out */
207 begin end
208 endcase
732b7730 209 end
5b3daee2 210endmodule
07fbfa80
JW
211
212module Multiplier(
213 input clk,
214 input Nrst, /* XXX not used yet */
215
216 input start,
217 input [31:0] acc0,
218 input [31:0] in0,
219 input [31:0] in1,
220
221 output reg done = 0,
222 output reg [31:0] result);
223
224 reg [31:0] bitfield;
225 reg [31:0] multiplicand;
226 reg [31:0] acc;
227
228 always @(posedge clk)
229 begin
230 if (start) begin
231 bitfield <= in0;
232 multiplicand <= in1;
233 acc <= acc0;
234 done <= 0;
235 end else begin
236 bitfield <= {2'b00, bitfield[31:2]};
237 multiplicand <= {multiplicand[29:0], 2'b00};
238 acc <= acc +
239 (bitfield[0] ? multiplicand : 0) +
240 (bitfield[1] ? {multiplicand[30:0], 1'b0} : 0);
241 if (bitfield == 0) begin
242 result <= acc;
243 done <= 1;
244 end
245 end
246 end
247endmodule
879a3986 248
879a3986
CL
249module ALU(
250 input clk,
251 input Nrst, /* XXX not used yet */
252
253 input [31:0] in0,
254 input [31:0] in1,
255 input [31:0] cpsr,
256 input [3:0] op,
257 input setflags,
258 input shifter_carry,
259
260 output reg [31:0] result,
261 output reg [31:0] cpsr_out,
732b7730 262 output reg setres
879a3986 263);
7947b9c7
JW
264 reg [31:0] res;
265 reg flag_n, flag_z, flag_c, flag_v;
879a3986 266 wire [32:0] sum, diff, rdiff;
793482e9 267 wire sum_v, diff_v, rdiff_v;
879a3986
CL
268
269 assign sum = {1'b0, in0} + {1'b0, in1};
270 assign diff = {1'b0, in0} - {1'b0, in1};
a4c270c7 271 assign rdiff = {1'b0, in1} - {1'b0, in0};
793482e9
CL
272 assign sum_v = (in0[31] ^~ in1[31]) & (sum[31] ^ in0[31]);
273 assign diff_v = (in0[31] ^ in1[31]) & (diff[31] ^ in0[31]);
274 assign rdiff_v = (in0[31] ^ in1[31]) & (rdiff[31] ^ in1[31]);
879a3986 275
879a3986
CL
276 always @(*) begin
277 res = 32'hxxxxxxxx;
278 setres = 1'bx;
279 flag_c = cpsr[`CPSR_C];
280 flag_v = cpsr[`CPSR_V];
281 case(op)
282 `ALU_AND: begin
732b7730 283 result = in0 & in1;
879a3986
CL
284 flag_c = shifter_carry;
285 setres = 1'b1;
286 end
287 `ALU_EOR: begin
732b7730 288 result = in0 ^ in1;
879a3986
CL
289 flag_c = shifter_carry;
290 setres = 1'b1;
291 end
292 `ALU_SUB: begin
732b7730 293 {flag_c, result} = diff;
1bc060d9 294 flag_c = !flag_c;
793482e9 295 flag_v = diff_v;
879a3986
CL
296 setres = 1'b1;
297 end
298 `ALU_RSB: begin
732b7730 299 {flag_c, result} = rdiff;
1bc060d9 300 flag_c = !flag_c;
793482e9 301 flag_v = rdiff_v;
879a3986
CL
302 setres = 1'b1;
303 end
304 `ALU_ADD: begin
732b7730 305 {flag_c, result} = sum;
793482e9 306 flag_v = sum_v;
879a3986
CL
307 setres = 1'b1;
308 end
309 `ALU_ADC: begin
732b7730 310 {flag_c, result} = sum + {32'b0, cpsr[`CPSR_C]};
793482e9 311 flag_v = sum_v | (~sum[31] & result[31]);
879a3986
CL
312 setres = 1'b1;
313 end
314 `ALU_SBC: begin
732b7730 315 {flag_c, result} = diff - {32'b0, (~cpsr[`CPSR_C])};
1bc060d9 316 flag_c = !flag_c;
793482e9 317 flag_v = diff_v | (diff[31] & ~result[31]);
879a3986
CL
318 setres = 1'b1;
319 end
320 `ALU_RSC: begin
732b7730 321 {flag_c, result} = rdiff - {32'b0, (~cpsr[`CPSR_C])};
1bc060d9 322 flag_c = !flag_c;
793482e9 323 flag_v = rdiff_v | (rdiff[31] & ~result[31]);
879a3986
CL
324 setres = 1'b1;
325 end
326 `ALU_TST: begin
732b7730 327 result = in0 & in1;
879a3986
CL
328 flag_c = shifter_carry;
329 setres = 1'b0;
330 end
331 `ALU_TEQ: begin
732b7730 332 result = in0 ^ in1;
879a3986
CL
333 flag_c = shifter_carry;
334 setres = 1'b0;
335 end
336 `ALU_CMP: begin
732b7730 337 {flag_c, result} = diff;
1bc060d9 338 flag_c = !flag_c;
793482e9 339 flag_v = diff_v;
879a3986
CL
340 setres = 1'b0;
341 end
342 `ALU_CMN: begin
732b7730 343 {flag_c, result} = sum;
793482e9 344 flag_v = sum_v;
879a3986
CL
345 setres = 1'b0;
346 end
347 `ALU_ORR: begin
732b7730 348 result = in0 | in1;
879a3986
CL
349 flag_c = shifter_carry;
350 setres = 1'b1;
351 end
352 `ALU_MOV: begin
732b7730 353 result = in1;
879a3986
CL
354 flag_c = shifter_carry;
355 setres = 1'b1;
356 end
357 `ALU_BIC: begin
732b7730 358 result = in0 & (~in1);
879a3986
CL
359 flag_c = shifter_carry;
360 setres = 1'b1;
361 end
362 `ALU_MVN: begin
732b7730 363 result = ~in1;
879a3986
CL
364 flag_c = shifter_carry;
365 setres = 1'b1;
366 end
367 endcase
732b7730
JW
368
369 flag_z = (result == 0);
370 flag_n = result[31];
371
372 cpsr_out = setflags ? {flag_n, flag_z, flag_c, flag_v, cpsr[27:0]} : cpsr;
879a3986 373 end
879a3986 374endmodule
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