riscv/rocket-chip
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changed branch addr generation to get it off critical path

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This commit is contained in:
Rimas Avizienis 2011-12-02 01:56:17 -08:00
parent cf1965493b
commit e70b41241c
2 changed files with 8 additions and 5 deletions
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6
rocket/src/main/scala/ctrl.scala
View File

@ -37,6 +37,8 @@ class ioCtrlDpath extends Bundle()
val mem_eret = Bool('output);
val mem_load = Bool('output);
val wen = Bool('output);
// instruction in execute is an unconditional jump
val ex_jmp = Bool('output);
// enable/disable interrupts
val irq_enable = Bool('output);
val irq_disable = Bool('output);
@ -411,6 +413,7 @@ class rocketCtrl extends Component
ex_reg_xcpt_syscall <== id_syscall.toBool;
}
val beq = io.dpath.br_eq;
val bne = ~io.dpath.br_eq;
val blt = io.dpath.br_lt;
@ -428,6 +431,7 @@ class rocketCtrl extends Component
val jr_taken = (ex_reg_br_type === BR_JR);
val j_taken = (ex_reg_br_type === BR_J);
io.dpath.ex_jmp := j_taken;
io.dmem.req_val := ex_reg_mem_val && ~io.dpath.killx;
io.dmem.req_cmd := ex_reg_mem_cmd;
@ -538,9 +542,9 @@ class rocketCtrl extends Component
Mux(mem_reg_eret, PC_PCR, // eret instruction
Mux(replay_ex, PC_EX, // D$ blocked, D$ miss, privileged inst
Mux(!ex_reg_btb_hit && br_taken, PC_BR, // mispredicted taken branch
Mux(j_taken, PC_BR, // jump
Mux(ex_reg_btb_hit && !br_taken, PC_EX4, // mispredicted not taken branch
Mux(jr_taken, PC_JR, // jump register
Mux(j_taken, PC_J, // jump
Mux(io.dpath.btb_hit, PC_BTB, // predicted PC from BTB
PC_4))))))))); // PC+4

7
rocket/src/main/scala/dpath.scala
View File

@ -127,8 +127,8 @@ class rocketDpath extends Component
// FIXME: which bits to extract should be calculated based on VADDR_BITS
val branch_adder_rhs =
Mux(io.ctrl.sel_pc === PC_BR, Cat(ex_sign_extend_split(41,0), UFix(0, 1)),
Cat(Fill(17, ex_reg_inst(31)), ex_reg_inst(31,7), UFix(0, 1)));
Mux(io.ctrl.ex_jmp, Cat(Fill(17, ex_reg_inst(31)), ex_reg_inst(31,7), UFix(0,1)),
Cat(ex_sign_extend_split(41,0), UFix(0, 1)));
val ex_branch_target = ex_reg_pc + branch_adder_rhs.toUFix;
@ -140,12 +140,11 @@ class rocketDpath extends Component
Mux(io.ctrl.sel_pc === PC_EX, ex_reg_pc,
Mux(io.ctrl.sel_pc === PC_EX4, ex_reg_pc_plus4,
Mux(io.ctrl.sel_pc === PC_BR, ex_branch_target,
Mux(io.ctrl.sel_pc === PC_J, ex_branch_target,
Mux(io.ctrl.sel_pc === PC_JR, ex_jr_target.toUFix,
Mux(io.ctrl.sel_pc === PC_PCR, mem_reg_wdata(VADDR_BITS-1,0), // only used for ERET
Mux(io.ctrl.sel_pc === PC_EVEC, pcr.io.evec,
Mux(io.ctrl.sel_pc === PC_MEM, mem_reg_pc,
UFix(0, VADDR_BITS)))))))))));
UFix(0, VADDR_BITS))))))))));
when (!io.ctrl.stallf && io.host.start) {
if_reg_pc <== if_next_pc.toUFix;