9bfb03ddf9e63c6b3c21c6a4b7bbf735faf67136
[firearm.git] / Decode.v
1 `include "ARM_Constants.v"
2
3 module Decode(
4         input clk,
5         input [31:0] insn,
6         input [31:0] inpc,
7         input [31:0] incpsr,
8         input [31:0] inspsr,
9         output reg [31:0] op0,
10         output reg [31:0] op1,
11         output reg [31:0] op2,
12         output reg carry,
13         output reg [31:0] outcpsr,
14         output reg [31:0] outspsr,
15
16         output reg [3:0] read_0,
17         output reg [3:0] read_1,
18         output reg [3:0] read_2,
19         input [31:0] rdata_0,
20         input [31:0] rdata_1,
21         input [31:0] rdata_2
22         );
23
24         wire [31:0] regs0, regs1, regs2;
25         reg [31:0] rpc;
26         reg [31:0] op0_out, op1_out, op2_out;
27         reg carry_out;
28
29         /* shifter stuff */
30         wire [31:0] shift_oper;
31         wire [31:0] shift_res;
32         wire shift_cflag_out;
33         wire [31:0] rotate_res;
34
35         assign regs0 = (read_0 == 4'b1111) ? rpc : rdata_0;
36         assign regs1 = (read_1 == 4'b1111) ? rpc : rdata_1;
37         assign regs2 = rdata_2; /* use regs2 for things that cannot be r15 */
38
39         IREALLYHATEARMSHIFT shift(.insn(insn),
40                                   .operand(regs1),
41                                   .reg_amt(regs2),
42                                   .cflag_in(incpsr[`CPSR_C]),
43                                   .res(shift_res),
44                                   .cflag_out(shift_cflag_out));
45
46         SuckLessRotator whirr(.oper({24'b0, insn[7:0]}),
47                               .amt(insn[11:8]),
48                               .res(rotate_res));
49
50         always @(*)
51                 casez (insn)
52                 `DECODE_ALU_MULT,               /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
53 //              `DECODE_ALU_MUL_LONG,           /* Multiply long */
54                 `DECODE_ALU_MRS,                /* MRS (Transfer PSR to register) */
55                 `DECODE_ALU_MSR,                /* MSR (Transfer register to PSR) */
56                 `DECODE_ALU_MSR_FLAGS,          /* MSR (Transfer register or immediate to PSR, flag bits only) */
57                 `DECODE_ALU_SWP,                /* Atomic swap */
58                 `DECODE_ALU_BX,                 /* Branch and exchange */
59                 `DECODE_ALU_HDATA_REG,          /* Halfword transfer - register offset */
60                 `DECODE_ALU_HDATA_IMM,          /* Halfword transfer - register offset */
61                 `DECODE_LDRSTR_UNDEFINED,       /* Undefined. I hate ARM */
62                 `DECODE_LDRSTR,                 /* Single data transfer */
63                 `DECODE_LDMSTM,                 /* Block data transfer */
64                 `DECODE_BRANCH,                 /* Branch */
65                 `DECODE_LDCSTC,                 /* Coprocessor data transfer */
66                 `DECODE_CDP,                    /* Coprocessor data op */
67                 `DECODE_SWI:                    /* SWI */
68                         rpc = inpc + 8;
69                 `DECODE_MRCMCR:                 /* Coprocessor register transfer */
70                         rpc = inpc + 12;
71                 `DECODE_ALU:                    /* ALU */
72                         rpc = inpc + (insn[25] ? 8 : (insn[4] ? 12 : 8));
73                 default:                        /* X everything else out */
74                         rpc = 32'hxxxxxxxx;
75                 endcase
76         
77         always @(*) begin
78                 read_0 = 4'hx;
79                 read_1 = 4'hx;
80                 read_2 = 4'hx;
81                 
82                 op0_out = 32'hxxxxxxxx;
83                 op1_out = 32'hxxxxxxxx;
84                 op2_out = 32'hxxxxxxxx;
85                 carry_out = 1'bx;
86                 
87                 casez (insn)
88                 `DECODE_ALU_MULT:       /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
89                 begin
90                         read_0 = insn[15:12]; /* Rn */
91                         read_1 = insn[3:0];   /* Rm */
92                         read_2 = insn[11:8];  /* Rs */
93                         
94                         op0_out = regs0;
95                         op1_out = regs1;
96                         op2_out = regs2;
97                 end
98 //              `DECODE_ALU_MUL_LONG:   /* Multiply long */
99 //              begin
100 //                      read_0 = insn[11:8]; /* Rn */
101 //                      read_1 = insn[3:0];   /* Rm */
102 //                      read_2 = 4'b0;       /* anyus */
103 //
104 //                      op1_res = regs1;
105 //              end
106                 `DECODE_ALU_MRS:        /* MRS (Transfer PSR to register) */
107                 begin end
108                 `DECODE_ALU_MSR:        /* MSR (Transfer register to PSR) */
109                 begin
110                         read_0 = insn[3:0];     /* Rm */
111                         
112                         op0_out = regs0;
113                 end
114                 `DECODE_ALU_MSR_FLAGS:  /* MSR (Transfer register or immediate to PSR, flag bits only) */
115                 begin
116                         read_0 = insn[3:0];     /* Rm */
117                         
118                         if(insn[25]) begin     /* the constant case */
119                                 op0_out = rotate_res;
120                         end else begin
121                                 op0_out = regs0;
122                         end
123                 end
124                 `DECODE_ALU_SWP:        /* Atomic swap */
125                 begin
126                         read_0 = insn[19:16]; /* Rn */
127                         read_1 = insn[3:0];   /* Rm */
128                         
129                         op0_out = regs0;
130                         op1_out = regs1;
131                 end
132                 `DECODE_ALU_BX:         /* Branch and exchange */
133                 begin
134                         read_0 = insn[3:0];   /* Rn */
135                         
136                         op0_out = regs0;
137                 end
138                 `DECODE_ALU_HDATA_REG:  /* Halfword transfer - register offset */
139                 begin
140                         read_0 = insn[19:16];
141                         read_1 = insn[3:0];
142                         read_2 = insn[15:12];
143
144                         op0_out = regs0;
145                         op1_out = regs1;
146                         op2_out = regs2;
147                 end
148                 `DECODE_ALU_HDATA_IMM:  /* Halfword transfer - immediate offset */
149                 begin
150                         read_0 = insn[19:16];
151                         read_1 = insn[15:12];
152                         
153                         op0_out = regs0;
154                         op1_out = {24'b0, insn[11:8], insn[3:0]};
155                         op2_out = regs1;
156                 end
157                 `DECODE_ALU:            /* ALU */
158                 begin
159                         read_0 = insn[19:16]; /* Rn */
160                         read_1 = insn[3:0];   /* Rm */
161                         read_2 = insn[11:8];  /* Rs for shift */
162                         
163                         op0_out = regs0;
164                         if(insn[25]) begin     /* the constant case */
165                                 carry_out = incpsr[`CPSR_C];
166                                 op1_out = rotate_res;
167                         end else begin
168                                 carry_out = shift_cflag_out;
169                                 op1_out = shift_res;
170                         end
171                 end
172                 `DECODE_LDRSTR_UNDEFINED:       /* Undefined. I hate ARM */
173                 begin
174                         /* eat shit */
175                 end
176                 `DECODE_LDRSTR:         /* Single data transfer */
177                 begin
178                         read_0 = insn[19:16]; /* Rn */
179                         read_1 = insn[3:0];   /* Rm */
180                         read_2 = insn[15:12];
181                         
182                         op0_out = regs0;
183                         if(insn[25]) begin
184                                 op1_out = {20'b0, insn[11:0]};
185                                 carry_out = incpsr[`CPSR_C];
186                         end else begin
187                                 op1_out = shift_res;
188                                 carry_out = shift_cflag_out;
189                         end
190                         op2_out = regs2;
191                 end
192                 `DECODE_LDMSTM:         /* Block data transfer */
193                 begin
194                         read_0 = insn[19:16];
195                         
196                         op0_out = regs0;
197                         op1_out = {16'b0, insn[15:0]};
198                 end
199                 `DECODE_BRANCH:         /* Branch */
200                 begin
201                         op0_out = {{6{insn[23]}}, insn[23:0], 2'b0};
202                 end
203                 `DECODE_LDCSTC:         /* Coprocessor data transfer */
204                 begin
205                         read_0 = insn[19:16];
206                         
207                         op0_out = regs0;
208                         op1_out = {24'b0, insn[7:0]};
209                 end
210                 `DECODE_CDP:            /* Coprocessor data op */
211                 begin
212                 end
213                 `DECODE_MRCMCR:         /* Coprocessor register transfer */
214                 begin
215                         read_0 = insn[15:12];
216                         
217                         op0_out = regs0;
218                 end
219                 `DECODE_SWI:            /* SWI */
220                 begin
221                 end
222                 default:
223                         $display("Undecoded instruction");
224                 endcase
225         end
226
227         
228         always @ (posedge clk) begin
229                 op0 <= op0_out;   /* Rn - always */
230                 op1 <= op1_out; /* 'operand 2' - Rm */
231                 op2 <= op2_out;   /* thirdedge - Rs */
232                 carry <= carry_out;
233                 outcpsr <= incpsr;
234                 outspsr <= inspsr;
235         end
236
237 endmodule
238
239 module IREALLYHATEARMSHIFT(
240         input [31:0] insn,
241         input [31:0] operand,
242         input [31:0] reg_amt,
243         input cflag_in,
244         output reg [31:0] res,
245         output reg cflag_out
246 );
247         wire [5:0] shift_amt;
248         reg is_arith, is_rot;
249         wire rshift_cout;
250         wire [31:0] rshift_res;
251
252         assign shift_amt = insn[4] ? {|reg_amt[7:5], reg_amt[4:0]}     /* reg-specified shift */
253                                    : {insn[11:7] == 5'b0, insn[11:7]}; /* immediate shift */
254
255         SuckLessShifter barrel(.oper(operand),
256                                .carryin(cflag_in),
257                                .amt(shift_amt),
258                                .is_arith(is_arith),
259                                .is_rot(is_rot),
260                                .res(rshift_res),
261                                .carryout(rshift_cout));
262
263         always @(*)
264                 case (insn[6:5])
265                 `SHIFT_LSL: begin
266                         /* meaningless */
267                         is_rot = 1'b0;
268                         is_arith = 1'b0;
269                 end
270                 `SHIFT_LSR: begin
271                         is_rot = 1'b0;
272                         is_arith = 1'b0;
273                 end
274                 `SHIFT_ASR: begin
275                         is_rot = 1'b0;
276                         is_arith = 1'b1;
277                 end
278                 `SHIFT_ROR: begin
279                         is_rot = 1'b1;
280                         is_arith = 1'b0;
281                 end
282                 endcase
283
284         always @(*)
285                 case (insn[6:5]) /* shift type */
286                 `SHIFT_LSL:
287                         {cflag_out, res} = {cflag_in, operand} << {insn[4] & shift_amt[5], shift_amt[4:0]};
288                 `SHIFT_LSR: begin
289                         res = rshift_res;
290                         cflag_out = rshift_cout;
291                 end
292                 `SHIFT_ASR: begin
293                         res = rshift_res;
294                         cflag_out = rshift_cout;
295                 end
296                 `SHIFT_ROR: begin
297                         if(!insn[4] && shift_amt[4:0] == 5'b0) begin /* RRX x.x */
298                                 res = {cflag_in, operand[31:1]};
299                                 cflag_out = operand[0];
300                         end else begin
301                                 res = rshift_res;
302                                 cflag_out = rshift_cout;
303                         end
304                 end
305                 endcase
306 endmodule
307
308 module SuckLessShifter(
309         input [31:0] oper,
310         input carryin,
311         input [5:0] amt,
312         input is_arith,
313         input is_rot,
314         output wire [31:0] res,
315         output wire carryout
316 );
317
318         wire [32:0] stage1, stage2, stage3, stage4, stage5;
319
320         wire pushbits = is_arith & oper[31];
321
322         /* do a barrel shift */
323         assign stage1 = amt[5] ? {is_rot ? oper : {32{pushbits}}, oper[31]} : {oper, carryin};
324         assign stage2 = amt[4] ? {is_rot ? stage1[16:1] : {16{pushbits}}, stage1[32:17], stage1[16]} : stage1;
325         assign stage3 = amt[3] ? {is_rot ? stage2[8:1] : {8{pushbits}}, stage2[32:9], stage2[8]} : stage2;
326         assign stage4 = amt[2] ? {is_rot ? stage3[4:1] : {4{pushbits}}, stage3[32:5], stage3[4]} : stage3;
327         assign stage5 = amt[1] ? {is_rot ? stage4[2:1] : {2{pushbits}}, stage4[32:3], stage4[2]} : stage4;
328         assign {res, carryout} = amt[0] ? {is_rot ? stage5[1] : pushbits, stage5[32:2], stage5[1]} : stage5;
329
330 endmodule
331
332 module SuckLessRotator(
333         input [31:0] oper,
334         input [3:0] amt,
335         output wire [31:0] res
336 );
337
338         wire [31:0] stage1, stage2, stage3;
339         assign stage1 = amt[3] ? {oper[15:0], oper[31:16]} : oper;
340         assign stage2 = amt[2] ? {stage1[7:0], stage1[31:8]} : stage1;
341         assign stage3 = amt[1] ? {stage2[3:0], stage2[31:4]} : stage2;
342         assign res    = amt[0] ? {stage3[1:0], stage3[31:2]} : stage3;
343
344 endmodule
345
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