From c98c0dd3e05c3f81698913e39c2a377fb3077fd4 Mon Sep 17 00:00:00 2001
From: Rose Thompson <ross1728@gmail.com>
Date: Wed, 13 Dec 2023 13:05:10 -0600
Subject: [PATCH] Removed unnecessary pc reset logic from ifu and btb.

---
 src/ifu/bpred/btb.sv | 8 +-------
 src/ifu/ifu.sv       | 7 +++----
 2 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/src/ifu/bpred/btb.sv b/src/ifu/bpred/btb.sv
index 066176daa..567e4d3cd 100644
--- a/src/ifu/bpred/btb.sv
+++ b/src/ifu/bpred/btb.sv
@@ -50,7 +50,6 @@ module btb import cvw::*;  #(parameter cvw_t P,
 );
 
   logic [Depth-1:0]        PCNextFIndex, PCFIndex, PCDIndex, PCEIndex, PCMIndex, PCWIndex;
-  logic [P.XLEN-1:0]        ResetPC;
   logic                    MatchD, MatchE, MatchM, MatchW, MatchX;
   logic [P.XLEN+3:0]        ForwardBTBPrediction, ForwardBTBPredictionF;
   logic [P.XLEN+3:0]        TableBTBPredF;
@@ -70,12 +69,7 @@ module btb import cvw::*;  #(parameter cvw_t P,
   assign PCMIndex = {PCM[Depth+1] ^ PCM[1], PCM[Depth:2]};
   assign PCWIndex = {PCW[Depth+1] ^ PCW[1], PCW[Depth:2]};
 
-  // must output a valid PC and valid bit during reset.  Because only PCF, not PCNextF is reset, PCNextF is invalid
-  // during reset.  The BTB must produce a non X PC1NextF to allow the simulation to run.
-  // While the mux could be included in IFU it is not necessary for the IROM/I$/bus.
-  // For now it is optimal to leave it here.
-  assign ResetPC = P.RESET_VECTOR[P.XLEN-1:0];
-  assign PCNextFIndex = reset ? ResetPC[Depth+1:2] : {PCNextF[Depth+1] ^ PCNextF[1], PCNextF[Depth:2]}; 
+  assign PCNextFIndex = {PCNextF[Depth+1] ^ PCNextF[1], PCNextF[Depth:2]}; 
 
   assign MatchD = PCFIndex == PCDIndex;
   assign MatchE = PCFIndex == PCEIndex;
diff --git a/src/ifu/ifu.sv b/src/ifu/ifu.sv
index 4a02848b5..7ebdd5878 100644
--- a/src/ifu/ifu.sv
+++ b/src/ifu/ifu.sv
@@ -300,8 +300,8 @@ module ifu import cvw::*;  #(parameter cvw_t P) (
     mux2 #(P.XLEN) pcmux2(.d0(PC1NextF), .d1(NextValidPCE), .s(CSRWriteFenceM),.y(PC2NextF));
   else assign PC2NextF = PC1NextF;
 
-  assign  PCNextF = {UnalignedPCNextF[P.XLEN-1:1], 1'b0}; // hart-SPEC p. 21 about 16-bit alignment
-  flopenl #(P.XLEN) pcreg(clk, reset, ~StallF, PCNextF, P.RESET_VECTOR[P.XLEN-1:0], PCF);
+  mux2 #(P.XLEN) pcresetmux({UnalignedPCNextF[P.XLEN-1:1], 1'b0}, P.RESET_VECTOR[P.XLEN-1:0], reset, PCNextF);
+  flopen #(P.XLEN) pcreg(clk, ~StallF | reset, PCNextF, PCF);
 
   // pcadder
   // add 2 or 4 to the PC, based on whether the instruction is 16 bits or 32
@@ -315,8 +315,7 @@ module ifu import cvw::*;  #(parameter cvw_t P) (
   // an X.  This version of the code does not die because if CompressedF is an X it just defaults to the last
   // option.  The above code would work, but propagates the x.
   always_comb
-    if(reset) PCPlus2or4F = '0;
-    else if (CompressedF) // add 2
+    if (CompressedF) // add 2
       if (PCF[1]) PCPlus2or4F = {PCPlus4F, 2'b00}; 
       else        PCPlus2or4F = {PCF[P.XLEN-1:2], 2'b10};
     else          PCPlus2or4F = {PCPlus4F, PCF[1:0]}; // add 4