Possible fix for wfi.

src/hazard/hazard.sv

@@ -27,6 +27,7 @@
 ////////////////////////////////////////////////////////////////////////////////////////////////
 
 module hazard (
+  input  logic clk, reset,
   // Detect hazards
   input  logic  BPWrongE, CSRWriteFenceM, RetM, TrapM,   
   input  logic  LoadStallD, StoreStallD, MDUStallD, CSRRdStallD,
@@ -45,10 +46,12 @@ module hazard (
   logic                                       FlushDCause, FlushECause, FlushMCause, FlushWCause;
 
   logic WFIStallM, WFIInterruptedM;
+  logic wfiW;
 
   // WFI logic
-  assign WFIStallM = wfiM & ~IntPendingM;         // WFI waiting for an interrupt or timeout
+  flopenrc #(1) wfiWReg(clk, reset, FlushW, ~StallW, wfiM, wfiW);
-  assign WFIInterruptedM = wfiM & IntPendingM;    // WFI detects a pending interrupt.  Retire WFI; trap if interrupt is enabled.
+  assign WFIStallM = wfiW & ~IntPendingM;         // WFI waiting for an interrupt or timeout
+  assign WFIInterruptedM = wfiW & IntPendingM;    // WFI detects a pending interrupt.  Retire WFI; trap if interrupt is enabled.
   
   // stalls and flushes
   // loads: stall for one cycle if the subsequent instruction depends on the load
@@ -73,7 +76,8 @@ module hazard (
   assign FlushDCause = TrapM | RetM | CSRWriteFenceM | BPWrongE;
   assign FlushECause = TrapM | RetM | CSRWriteFenceM |(BPWrongE & ~(DivBusyE | FDivBusyE));
   assign FlushMCause = TrapM | RetM | CSRWriteFenceM;
-  assign FlushWCause = TrapM & ~WFIInterruptedM;
+  //assign FlushWCause = TrapM & ~WFIInterruptedM;
+  assign FlushWCause = TrapM;
 
   // Stall causes
   //  Most data depenency stalls are identified in the decode stage
@@ -86,11 +90,13 @@ module hazard (
   assign StallFCause = '0;
   assign StallDCause = (LoadStallD | StoreStallD | MDUStallD | CSRRdStallD | FCvtIntStallD | FPUStallD) & ~FlushDCause;
   assign StallECause = (DivBusyE | FDivBusyE) & ~FlushECause; 
-  assign StallMCause = WFIStallM & ~FlushMCause; 
+  //assign StallMCause = WFIStallM & ~FlushMCause;
+  assign StallMCause = '0; 
   // Need to gate IFUStallF when the equivalent FlushFCause = FlushDCause = 1.
   // assign StallWCause = ((IFUStallF & ~FlushDCause) | LSUStallM) & ~FlushWCause;
   // Because FlushWCause is a strict subset of FlushDCause, FlushWCause is factored out.
-  assign StallWCause = (IFUStallF & ~FlushDCause) | (LSUStallM & ~FlushWCause);
+  //assign StallWCause = (IFUStallF & ~FlushDCause) | (LSUStallM & ~FlushWCause);
+  assign StallWCause = (IFUStallF & ~FlushDCause) | ((LSUStallM | WFIStallM) & ~FlushWCause);
 
   // Stall each stage for cause or if the next stage is stalled
   // coverage off: StallFCause is always 0

src/privileged/csr.sv

@@ -200,9 +200,13 @@ module csr import cvw::*;  #(parameter cvw_t P) (
   ///////////////////////////////////////////
   // CSR Write values
   ///////////////////////////////////////////
+  logic [P.XLEN-1:0] PCW; // *** can optimize out it's just PCM for all now.
+  logic              wfiW;
+  flopenr #(P.XLEN) PCWReg(clk, reset, ~StallW, PCM, PCW);
+  flopenrc #(1) wfiWReg(clk, reset, FlushW, ~StallW, wfiM, wfiW);
 
   assign CSRAdrM = InstrM[31:20];
-  assign UnalignedNextEPCM = TrapM ? ((wfiM & IntPendingM) ? PCM+4 : PCM) : CSRWriteValM;
+  assign UnalignedNextEPCM = TrapM ? ((wfiW & IntPendingM) ? PCW+4 : PCM) : CSRWriteValM;
   assign NextEPCM = P.C_SUPPORTED ? {UnalignedNextEPCM[P.XLEN-1:1], 1'b0} : {UnalignedNextEPCM[P.XLEN-1:2], 2'b00}; // 3.1.15 alignment
   assign NextCauseM = TrapM ? {InterruptM, CauseM}: {CSRWriteValM[P.XLEN-1], CSRWriteValM[3:0]};
   assign NextMtvalM = TrapM ? NextFaultMtvalM : CSRWriteValM;

src/wally/wallypipelinedcore.sv

@@ -264,7 +264,7 @@ module wallypipelinedcore import cvw::*; #(parameter cvw_t P) (
   end
 
   // global stall and flush control  
-  hazard  hzu(
+  hazard  hzu(.clk, .reset,
     .BPWrongE, .CSRWriteFenceM, .RetM, .TrapM,
     .LoadStallD, .StoreStallD, .MDUStallD, .CSRRdStallD,
     .LSUStallM, .IFUStallF,