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