From 05b755958fbe148ee2e18a2fe0983497fc5da45f Mon Sep 17 00:00:00 2001
From: David Harris <david_harris@hmc.edu>
Date: Thu, 28 Jan 2021 21:40:48 -0500
Subject: [PATCH] Hint to optimize ifu

---
 riscv-o3                   | 2 +-
 wally-pipelined/src/ifu.sv | 6 ++++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/riscv-o3 b/riscv-o3
index a13ac64f..afb27bd5 160000
--- a/riscv-o3
+++ b/riscv-o3
@@ -1 +1 @@
-Subproject commit a13ac64fa50c187ffd489cdb2f4a4a70e60fc837
+Subproject commit afb27bd558a9b6fabb6b768ae81ef122b4db9eea
diff --git a/wally-pipelined/src/ifu.sv b/wally-pipelined/src/ifu.sv
index 30f864ae..3ba78dd4 100644
--- a/wally-pipelined/src/ifu.sv
+++ b/wally-pipelined/src/ifu.sv
@@ -106,8 +106,10 @@ module ifu (
   flopr #(`XLEN) PCMReg(clk, reset, PCE, PCM);
   flopr #(`XLEN) PCWReg(clk, reset, PCM, PCW); // *** probably not needed; delete later
 
-  // seems like there should be a lower-cost way of doing this PC+2 or PC+4 for JAL.  Maybe a way to draw on PC
-  // or just put an adder at the start of the writeback stage.
+  // seems like there should be a lower-cost way of doing this PC+2 or PC+4 for JAL.  
+  // either have ALU compute PC+2/4 and feed into ALUResult input of ResultMux or
+  // have dedicated adder in Mem stage based on PCM + 2 or 4
+  // *** redo this 
   flopr #(`XLEN) PCPDReg(clk, reset, PCPlus2or4F, PCLinkD);
   flopr #(`XLEN) PCPEReg(clk, reset, PCLinkD, PCLinkE);
   flopr #(`XLEN) PCPMReg(clk, reset, PCLinkE, PCLinkM);