riscv/rocket-chip
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use replay to handle I$ misses

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this eliminates a long path in the fetch stage
This commit is contained in:
Andrew Waterman
2012-01-11 19:20:20 -08:00
parent 1a7bfd4350
commit 4807d7222b
3 changed files with 23 additions and 18 deletions
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25
rocket/src/main/scala/ctrl.scala
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@ -290,10 +290,10 @@ class rocketCtrl extends Component
*/
));
val if_reg_xcpt_ma_inst = Reg(io.dpath.xcpt_ma_inst);
val if_reg_xcpt_ma_inst = Reg(io.dpath.xcpt_ma_inst, resetVal = Bool(false));
// FIXME
io.imem.req_val := !io.dpath.xcpt_ma_inst;
io.imem.req_val := Bool(true)
val id_int_val :: id_br_type :: id_renx2 :: id_renx1 :: id_sel_alu2 :: id_sel_alu1 :: id_fn_dw :: id_fn_alu :: csremainder = cs;
val id_mem_val :: id_mem_cmd :: id_mem_type :: id_mul_val :: id_mul_fn :: id_div_val :: id_div_fn :: id_wen :: id_sel_wa :: id_sel_wb :: id_ren_pcr :: id_wen_pcr :: id_irq :: id_sync :: id_eret :: id_syscall :: id_privileged :: Nil = csremainder;
@ -326,6 +326,7 @@ class rocketCtrl extends Component
val id_reg_btb_hit = Reg(resetVal = Bool(false));
val id_reg_xcpt_itlb = Reg(resetVal = Bool(false));
val id_reg_xcpt_ma_inst = Reg(resetVal = Bool(false));
val id_reg_icmiss = Reg(resetVal = Bool(false));
val ex_reg_br_type = Reg(){UFix(width = 4)};
val ex_reg_btb_hit = Reg(){Bool()};
@ -344,6 +345,7 @@ class rocketCtrl extends Component
val ex_reg_xcpt_privileged = Reg(resetVal = Bool(false));
val ex_reg_xcpt_fpu = Reg(resetVal = Bool(false));
val ex_reg_xcpt_syscall = Reg(resetVal = Bool(false));
val ex_reg_icmiss = Reg(resetVal = Bool(false));
val mem_reg_inst_di = Reg(resetVal = Bool(false));
val mem_reg_inst_ei = Reg(resetVal = Bool(false));
@ -356,6 +358,7 @@ class rocketCtrl extends Component
val mem_reg_xcpt_syscall = Reg(resetVal = Bool(false));
val mem_reg_replay = Reg(resetVal = Bool(false));
val mem_reg_kill_dmem = Reg(resetVal = Bool(false));
val mem_reg_icmiss = Reg(resetVal = Bool(false));
val wb_reg_inst_di = Reg(resetVal = Bool(false));
val wb_reg_inst_ei = Reg(resetVal = Bool(false));
@ -364,6 +367,8 @@ class rocketCtrl extends Component
val wb_reg_badvaddr_wen = Reg(resetVal = Bool(false));
val wb_reg_cause = Reg(){UFix()};
val take_pc = Wire() { Bool() };
when (!io.dpath.stalld) {
when (io.dpath.killf) {
id_reg_xcpt_ma_inst <== Bool(false);
@ -375,6 +380,7 @@ class rocketCtrl extends Component
id_reg_xcpt_itlb <== io.xcpt_itlb;
id_reg_btb_hit <== io.dpath.btb_hit;
}
id_reg_icmiss <== !take_pc && !io.imem.resp_val;
}
// executing ERET when traps are enabled causes an illegal instruction exception (as per ISA sim)
@ -397,6 +403,7 @@ class rocketCtrl extends Component
ex_reg_xcpt_privileged <== Bool(false);
ex_reg_xcpt_fpu <== Bool(false);
ex_reg_xcpt_syscall <== Bool(false);
ex_reg_icmiss <== Bool(false);
}
otherwise {
ex_reg_br_type <== id_br_type;
@ -415,6 +422,7 @@ class rocketCtrl extends Component
// ex_reg_xcpt_fpu <== id_fp_val.toBool;
ex_reg_xcpt_fpu <== Bool(false);
ex_reg_xcpt_syscall <== id_syscall.toBool;
ex_reg_icmiss <== id_reg_icmiss;
}
ex_reg_mem_cmd <== id_mem_cmd;
ex_reg_mem_type <== id_mem_type;
@ -462,6 +470,7 @@ class rocketCtrl extends Component
mem_reg_xcpt_privileged <== Bool(false);
mem_reg_xcpt_fpu <== Bool(false);
mem_reg_xcpt_syscall <== Bool(false);
mem_reg_icmiss <== Bool(false);
}
otherwise {
mem_reg_div_mul_val <== ex_reg_div_mul_val;
@ -477,6 +486,7 @@ class rocketCtrl extends Component
mem_reg_xcpt_privileged <== ex_reg_xcpt_privileged;
mem_reg_xcpt_fpu <== ex_reg_xcpt_fpu;
mem_reg_xcpt_syscall <== ex_reg_xcpt_syscall;
mem_reg_icmiss <== ex_reg_icmiss;
}
mem_reg_mem_cmd <== ex_reg_mem_cmd;
mem_reg_mem_type <== ex_reg_mem_type;
@ -550,7 +560,7 @@ class rocketCtrl extends Component
io.dpath.badvaddr_wen := wb_reg_badvaddr_wen;
// replay mem stage PC on a DTLB miss
val mem_hazard = io.dtlb_miss || io.dmem.resp_nack;
val mem_hazard = io.dtlb_miss || io.dmem.resp_nack || mem_reg_icmiss;
val mem_kill_dmem = io.dtlb_miss || mem_exception || mem_reg_kill_dmem;
val replay_mem = mem_hazard || mem_reg_replay;
val kill_mem = mem_hazard || mem_exception;
@ -560,7 +570,7 @@ class rocketCtrl extends Component
val br_jr_taken = br_taken || jr_taken
val take_pc_ex = !ex_btb_match && br_jr_taken || ex_reg_btb_hit && !br_jr_taken
val take_pc_mem = mem_exception || mem_reg_eret || replay_mem
val take_pc = take_pc_ex || take_pc_mem
take_pc <== take_pc_ex || take_pc_mem
// replay execute stage PC when the D$ is blocked, when the D$ misses,
// for privileged instructions, and for fence.i instructions
@ -583,12 +593,7 @@ class rocketCtrl extends Component
io.dpath.wen_btb := !ex_btb_match && br_jr_taken && !kill_ex;
io.dpath.stallf :=
~take_pc &
(
~io.imem.resp_val |
io.dpath.stalld
);
io.dpath.stallf := io.dpath.stalld;
// stall for RAW/WAW hazards on loads, AMOs, and mul/div in execute stage.
val ex_mem_cmd_load =