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VexRiscv
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Fix #69 discoverd fmax issue with decode stage branch predictions

This commit is contained in:
Charles Papon 2019-04-12 15:24:33 +02:00
parent fdd2194c8f
commit 63cd5f42af
2 changed files with 10 additions and 1 deletions
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2
src/main/scala/vexriscv/plugin/BranchPlugin.scala
View File

@ -268,7 +268,7 @@ class BranchPlugin(earlyBranch : Boolean,
default{
branch_src1 := input(PC)
branch_src2 := ((input(BRANCH_CTRL) === BranchCtrlEnum.JAL) ? imm.j_sext | imm.b_sext).asUInt
when(input(PREDICTION_HAD_BRANCHED) && ! missAlignedTarget){
when(input(PREDICTION_HAD_BRANCHED)){ //Assume the predictor never predict missaligned stuff, this avoid the need to know if the instruction should branch or not
branch_src2 := (if(pipeline(RVC_GEN)) Mux(input(IS_RVC), B(2), B(4)) else B(4)).asUInt.resized
}
}

9
src/main/scala/vexriscv/plugin/Fetcher.scala
View File

@ -488,6 +488,15 @@ abstract class IBusFetcherImpl(val resetVector : BigInt,
decodePrediction.cmd.hadBranch := decode.input(BRANCH_CTRL) === BranchCtrlEnum.JAL || (decode.input(BRANCH_CTRL) === BranchCtrlEnum.B && conditionalBranchPrediction)
val noPredictionOnMissaligned = (!pipeline(RVC_GEN)) generate new Area{
val missaligned = decode.input(BRANCH_CTRL).mux(
BranchCtrlEnum.JALR -> (imm.i_sext(1) ^ decode.input(RS1)(1)),
BranchCtrlEnum.JAL -> imm.j_sext(1),
default -> imm.b_sext(1)
)
decodePrediction.cmd.hadBranch clearWhen(missaligned)
}
predictionJumpInterface.valid := decodePrediction.cmd.hadBranch && decode.arbitration.isFiring //TODO OH Doublon de priorité
predictionJumpInterface.payload := decode.input(PC) + ((decode.input(BRANCH_CTRL) === BranchCtrlEnum.JAL) ? imm.j_sext | imm.b_sext).asUInt