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Hazard cleanup.

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This commit is contained in:
Ross Thompson 2022-12-15 10:05:17 -06:00
parent c253b882be
commit 8cd6a74c8f
1 changed files with 13 additions and 17 deletions
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30
pipelined/src/hazard/hazard.sv
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@ -46,6 +46,8 @@ module hazard(
logic StallFCause, StallDCause, StallECause, StallMCause, StallWCause; logic StallFCause, StallDCause, StallECause, StallMCause, StallWCause;
logic FirstUnstalledD, FirstUnstalledE, FirstUnstalledM, FirstUnstalledW; logic FirstUnstalledD, FirstUnstalledE, FirstUnstalledM, FirstUnstalledW;
logic FlushDCause, FlushECause, FlushMCause, FlushWCause;
// stalls and flushes // stalls and flushes
// loads: stall for one cycle if the subsequent instruction depends on the load // loads: stall for one cycle if the subsequent instruction depends on the load
@ -59,25 +61,21 @@ module hazard(
// A stage must stall if the next stage is stalled // A stage must stall if the next stage is stalled
// If any stages are stalled, the first stage that isn't stalled must flush. // If any stages are stalled, the first stage that isn't stalled must flush.
// *** can stalls be pushed into earlier stages (e.g. no stall after Decode?) assign FlushDCause = TrapM | RetM | BPPredWrongE | CSRWriteFenceM;
assign FlushECause = TrapM | RetM | BPPredWrongE | CSRWriteFenceM;
assign FlushMCause = TrapM | RetM | CSRWriteFenceM;
// on Trap the memory stage should be flushed going into the W stage,
// except if the instruction causing the Trap is an ecall or ebreak.
assign FlushWCause = TrapM & ~(BreakpointFaultM | EcallFaultM);
// *** consider replacing CSRWriteFencePendingDEM with a flush rather than a stall.
//assign StallFCause = CSRWriteFencePendingDEM & ~(TrapM | RetM | BPPredWrongE);
assign StallFCause = '0; assign StallFCause = '0;
// stall in decode if instruction is a load/mul/csr dependent on previous // stall in decode if instruction is a load/mul/csr dependent on previous
assign StallDCause = (LoadStallD | StoreStallD | MDUStallD | CSRRdStallD | FCvtIntStallD | FStallD) & ~(TrapM | RetM | BPPredWrongE | CSRWriteFenceM); assign StallDCause = (LoadStallD | StoreStallD | MDUStallD | CSRRdStallD | FCvtIntStallD | FStallD) & ~(FlushDCause);
assign StallECause = (DivBusyE | FDivBusyE) & ~(TrapM | CSRWriteFenceM); // *** can we move to decode stage (KP?) assign StallECause = (DivBusyE | FDivBusyE) & ~(TrapM | CSRWriteFenceM); // *** can we move to decode stage (KP?)
// WFI terminates if any enabled interrupt is pending, even if global interrupts are disabled. It could also terminate with TW trap // WFI terminates if any enabled interrupt is pending, even if global interrupts are disabled. It could also terminate with TW trap
assign StallMCause = ((wfiM) & (~TrapM & ~IntPendingM)); assign StallMCause = ((wfiM) & (~TrapM & ~IntPendingM));
assign StallWCause = ((IFUStallF | LSUStallM) & ~TrapM); // | (FDivBusyE & ~TrapM & ~IntPendingM); assign StallWCause = ((IFUStallF | LSUStallM) & ~TrapM); // | (FDivBusyE & ~TrapM & ~IntPendingM);
// head version
// assign StallWCause = LSUStallM | IFUStallF | (FDivBusyE & ~TrapM & ~IntPendingM); // *** FDivBusyE should look like DivBusyE
// assign StallMCause = (wfiM & (~TrapM & ~IntPendingM)); // | FDivBusyE;
// assign StallECause = (DivBusyE | FDivBusyE) & ~(TrapM); // *** can we move to decode stage (KP?)
// *** ross: my changes to cache and lsu need to disable ifu/lsu stalls on a Trap.
assign #1 StallF = StallFCause | StallD; assign #1 StallF = StallFCause | StallD;
assign #1 StallD = StallDCause | StallE; assign #1 StallD = StallDCause | StallE;
assign #1 StallE = StallECause | StallM; assign #1 StallE = StallECause | StallM;
@ -90,10 +88,8 @@ module hazard(
assign FirstUnstalledW = ~StallW & StallM; assign FirstUnstalledW = ~StallW & StallM;
// Each stage flushes if the previous stage is the last one stalled (for cause) or the system has reason to flush // Each stage flushes if the previous stage is the last one stalled (for cause) or the system has reason to flush
assign #1 FlushD = FirstUnstalledD | TrapM | RetM | BPPredWrongE | CSRWriteFenceM; assign #1 FlushD = FirstUnstalledD | FlushDCause;
assign #1 FlushE = FirstUnstalledE | TrapM | RetM | BPPredWrongE | CSRWriteFenceM ; // *** why is BPPredWrongE here, but not needed in simple processor assign #1 FlushE = FirstUnstalledE | FlushECause ; // *** why is BPPredWrongE here, but not needed in simple processor
assign #1 FlushM = FirstUnstalledM | TrapM | RetM | CSRWriteFenceM; assign #1 FlushM = FirstUnstalledM | FlushMCause;
// on Trap the memory stage should be flushed going into the W stage, assign #1 FlushW = FirstUnstalledW | FlushWCause;
// except if the instruction causing the Trap is an ecall or ebreak.
assign #1 FlushW = FirstUnstalledW | (TrapM & ~(BreakpointFaultM | EcallFaultM));
endmodule endmodule