From 17aebb8a3b943377e6815ae6f490baff37f61957 Mon Sep 17 00:00:00 2001
From: Ross Thompson <ross1728@gmail.com>
Date: Fri, 13 Jan 2023 18:05:47 -0600
Subject: [PATCH] Partial fix to RAS prediction accurracy.

---
 pipelined/src/ifu/RAsPredictor.sv | 16 +++++++++-------
 pipelined/src/ifu/bpred.sv        |  8 +++++++-
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/pipelined/src/ifu/RAsPredictor.sv b/pipelined/src/ifu/RAsPredictor.sv
index 3d82342fc..c71ff2966 100644
--- a/pipelined/src/ifu/RAsPredictor.sv
+++ b/pipelined/src/ifu/RAsPredictor.sv
@@ -32,12 +32,14 @@ module RASPredictor
   #(parameter int StackSize = 16
     )
   (input logic              clk,
-   input logic              reset,
-   input logic              PopF,
+   input logic 				reset,
+   input logic 				PopF,
    output logic [`XLEN-1:0] RASPCF,
-   input logic              PushE,
-   input logic              incr,
-   input logic [`XLEN-1:0]  PCLinkE
+   input logic [3:0] 		WrongPredInstrClassD,
+   input logic [3:0] 		InstrClassD,
+   input logic 				PushE,
+   input logic 				incr,
+   input logic [`XLEN-1:0] 	PCLinkE
    );
 
   // *** need to update so it either doesn't push until the memory stage
@@ -50,9 +52,9 @@ module RASPredictor
   logic [StackSize-1:0]     [`XLEN-1:0] memory;
   integer        index;
   
-  assign CounterEn = PopF | PushE | incr;
+  assign CounterEn = PopF | PushE | incr | WrongPredInstrClassD[2];
 
-  assign PtrD = PopF ? PtrM1 : PtrP1;
+  assign PtrD = PopF | InstrClassD[2] ? PtrM1 : PtrP1;
 
   assign PtrM1 = PtrQ - 1'b1;
   assign PtrP1 = PtrQ + 1'b1;
diff --git a/pipelined/src/ifu/bpred.sv b/pipelined/src/ifu/bpred.sv
index 53bd4bafd..38efe8fd5 100644
--- a/pipelined/src/ifu/bpred.sv
+++ b/pipelined/src/ifu/bpred.sv
@@ -79,7 +79,8 @@ module bpred (
   logic                     BPPredWrongM;
   logic [`XLEN-1:0]         PCNext0F;
   logic [`XLEN-1:0] 		PCCorrectE;
-
+  logic [3:0] 				WrongPredInstrClassD;
+  
   // Part 1 branch direction prediction
   // look into the 2 port Sram model. something is wrong. 
   if (`BPTYPE == "BPTWOBIT") begin:Predictor
@@ -157,6 +158,8 @@ module bpred (
   RASPredictor RASPredictor(.clk(clk),
        .reset(reset),
        .PopF(PredInstrClassF[2] & ~StallF),
+							.WrongPredInstrClassD,
+							.InstrClassD,
        .RASPCF,
        .PushE(InstrClassE[3] & ~StallE),
        .incr(1'b0),
@@ -213,6 +216,9 @@ module bpred (
   assign RASPredPCWrongE = InstrClassE[2] & PredictionPCWrongE;
   // Finally if the real instruction class is non CFI but the predictor said it was we need to count.
   assign BPPredClassNonCFIWrongE = PredictionInstrClassWrongE & ~|InstrClassE;
+
+  // branch class prediction wrong.
+  assign WrongPredInstrClassD = PredInstrClassD ^ InstrClassD;
   
   
   // Selects the BP or PC+2/4.