From 9d68d877d900272404f98d5af197fbe896d1eab1 Mon Sep 17 00:00:00 2001
From: Jonathan Woodruff <jdw57@cam.ac.uk>
Date: Wed, 9 Mar 2022 12:32:01 +0000
Subject: [PATCH] Move to much simpler design. Just update the head in Decode,
 and write data from Execute. A loop calling from the same place will at least
 find the correct address. Also, the bad fixup interaction is solved.

---
 .../RISCY_OOO/procs/RV64G_OOO/FetchStage.bsv  |  4 +--
 src_Core/RISCY_OOO/procs/lib/Ras.bsv          | 36 +++++++------------
 2 files changed, 14 insertions(+), 26 deletions(-)

diff --git a/src_Core/RISCY_OOO/procs/RV64G_OOO/FetchStage.bsv b/src_Core/RISCY_OOO/procs/RV64G_OOO/FetchStage.bsv
index 6f712f0..2fb92c2 100644
--- a/src_Core/RISCY_OOO/procs/RV64G_OOO/FetchStage.bsv
+++ b/src_Core/RISCY_OOO/procs/RV64G_OOO/FetchStage.bsv
@@ -470,7 +470,6 @@ module mkFetchStage(FetchStage);
 `ifdef PERFORMANCE_MONITORING
     Reg#(Bool) redirect_evt_reg <- mkDReg(False);
 `endif
-    Reg#(Bool) rasFixupDelay <- mkRegU;
 
     rule updatePcInBtb;
         nextAddrPred.put_pc(pc_reg[pc_final_port]);
@@ -1045,10 +1044,9 @@ module mkFetchStage(FetchStage);
             let last_x16_pc = addPc(pc, (isCompressed ? 0 : 2));
             napTrainByExe.wset(TrainNAP {pc: last_x16_pc, nextPc: next_pc});
 `ifdef SPEC_RSB_FIXUP
-            if (!rasFixupDelay) ras.setHead(trainInfo.ras);
+            ras.setHead(trainInfo.ras);
 `endif
         end
-        rasFixupDelay <= link;
     endmethod
 
     interface SpeculationUpdate specUpdate = main_epoch_spec.specUpdate;
diff --git a/src_Core/RISCY_OOO/procs/lib/Ras.bsv b/src_Core/RISCY_OOO/procs/lib/Ras.bsv
index 8f818cd..617f556 100644
--- a/src_Core/RISCY_OOO/procs/lib/Ras.bsv
+++ b/src_Core/RISCY_OOO/procs/lib/Ras.bsv
@@ -69,15 +69,6 @@ module mkRas(ReturnAddrStack) provisos(NumAlias#(TExp#(TLog#(RasEntries)), RasEn
     // head points past valid data
     // to gracefully overflow, head is allowed to overflow to 0 and overwrite the oldest data
     Ehr#(TAdd#(SupSize, 3), RasIndex) head <- mkEhr(0);
-    Ehr#(4, UInt#(3)) pendingPushReg <- mkEhr(0);
-
-    Reg#(Bit#(6)) pendingPushDelay <- mkReg(0);
-    rule updatePendingPushDelay;
-       if (pendingPushDelay > 60 || pendingPushReg[2] == 0) begin
-          pendingPushReg[2] <= 0;
-          pendingPushDelay <= 0;
-       end else pendingPushDelay <= pendingPushDelay + 1;
-    endrule
 
 `ifdef SECURITY
     Reg#(Bool) flushDone <- mkReg(True);
@@ -92,13 +83,7 @@ module mkRas(ReturnAddrStack) provisos(NumAlias#(TExp#(TLog#(RasEntries)), RasEn
     Vector#(SupSize, RAS) rasIfc;
     for(Integer i = 0; i < valueof(SupSize); i = i+1) begin
         rasIfc[i] = (interface RAS;
-            method CapMem first;
-                // If pendingPush is not zero, just take whetever was in the memory, as it is more likely
-                // to be correct than an unsynchronised entry (in case we keep calling the same function).
-                RasIndex pendingOffset = zeroExtend(pack(pendingPushReg[0]));
-                RasIndex h = head[i] + pendingOffset;
-                return  stack[h][0];
-            endmethod
+            method CapMem first = stack[head[i]][0];
             method ActionValue#(RasIndex) pop(Bool doPop);
                 RasIndex h = head[i];
                 if (doPop) begin
@@ -111,22 +96,27 @@ module mkRas(ReturnAddrStack) provisos(NumAlias#(TExp#(TLog#(RasEntries)), RasEn
     end
 
     method Action willPush;
-        pendingPushReg[0]._write(pendingPushReg[0] + 1);
-        $display("RAS willPushReg<-%d", pendingPushReg[0] + 1);
+        Reg#(RasIndex) h = head[valueof(SupSize) + 2];
+        h <= h+1;
+        $display("RAS head<-%d", h + 1);
     endmethod
-    method Bool pendingPush = (pendingPushReg[0] > 0 && pendingPushDelay < 6);
+    method Bool pendingPush = False;//(pendingPushReg[0] > 0 && pendingPushDelay < 6);
 
     method Action push(CapMem pushAddr);
+`ifdef NO_SPEC_RSB_PUSH
+        stack[head[0]][1] <= pushAddr;
+        $display("RAS push stack[%d] <- %x", head[0], pushAddr);
+`else
         Reg#(RasIndex) h = head[valueof(SupSize) + 2];
-        stack[h+1][1] <= pushAddr;
-        $display("RAS push head<-%d, val:%x, willPushReg<-%d", h+1, pushAddr, boundedMinus(pendingPushReg[1], 1));
         h <= h+1;
-        if (pendingPushReg[1] != 0) pendingPushReg[1] <= boundedMinus(pendingPushReg[1], 1);
+        stack[h+1][1] <= pushAddr;
+        $display("RAS push stack[%d] <- %x", head[0], pushAddr);
+        $display("RAS head<-%d", h + 1);
+`endif
     endmethod
 
     method Action setHead(RasIndex h);
         head[valueof(SupSize)] <= h;
-        pendingPushReg[3] <= 0;
         $display("RAS fixup head<-%d", h);
     endmethod