From f1e87c5e69e345c8d532b4ab4a11f2f79fdc83d5 Mon Sep 17 00:00:00 2001
From: David Harris <david_harris@hmc.edu>
Date: Fri, 24 Mar 2023 08:12:02 -0700
Subject: [PATCH] Start of EBU coverage tests

---
 src/ebu/ebufsmarb.sv | 27 +++++++++++++++-----------
 testbench/tests.vh   |  1 +
 tests/coverage/ebu.S | 45 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 62 insertions(+), 11 deletions(-)
 create mode 100644 tests/coverage/ebu.S

diff --git a/src/ebu/ebufsmarb.sv b/src/ebu/ebufsmarb.sv
index bd5cfb892..11d3eb2b6 100644
--- a/src/ebu/ebufsmarb.sv
+++ b/src/ebu/ebufsmarb.sv
@@ -56,7 +56,7 @@ module ebufsmarb (
   logic 	     IFUReqD;                    // 1 cycle delayed IFU request. Part of arbitration
   logic 	     FinalBeat, FinalBeatD;      // Indicates the last beat of a burst
   logic 	     BeatCntEn;
-  logic [4-1:0]      NextBeatCount, BeatCount;   // Position within a burst transfer
+  logic [3:0]      BeatCount;   // Position within a burst transfer
   logic 	     CntReset;
   logic [3:0] 	     Threshold;                  // Number of beats derived from HBURST
 
@@ -91,31 +91,36 @@ module ebufsmarb (
   // This is necessary because the pipeline is stalled for the entire duration of both transactions,
   // and the LSU memory request will stil be active.
   flopr #(1) ifureqreg(HCLK, ~HRESETn, IFUReq, IFUReqD);
-  assign LSUDisable = CurrState == ARBITRATE ? 1'b0 : (IFUReqD & ~(HREADY & FinalBeatD));
-  assign LSUSelect = NextState == ARBITRATE ? 1'b1: LSUReq;
+  assign LSUDisable = (CurrState == ARBITRATE) ? 1'b0 : (IFUReqD & ~(HREADY & FinalBeatD));
+  assign LSUSelect = (NextState == ARBITRATE) ? 1'b1: LSUReq;
 
   ////////////////////////////////////////////////////////////////////////////////////////////////////
   // Burst mode logic
   ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-  flopenr #(4) BeatCountReg(HCLK, ~HRESETn | CntReset | FinalBeat, BeatCntEn, NextBeatCount, BeatCount);  
-  assign NextBeatCount = BeatCount + 1'b1;
-
   assign CntReset = NextState == IDLE;
   assign FinalBeat = (BeatCount == Threshold); // Detect when we are waiting on the final access.
-  assign BeatCntEn = (NextState == ARBITRATE & HREADY);
-
+  assign BeatCntEn = (NextState == ARBITRATE) & HREADY;
+  counter #(4) BeatCounter(HCLK, ~HRESETn | CntReset | FinalBeat, BeatCntEn, BeatCount);  
+ 
   // Used to store data from data phase of AHB.
   flopenr #(1) FinalBeatReg(HCLK, ~HRESETn | CntReset, BeatCntEn, FinalBeat, FinalBeatD);
 
   // unlike the bus fsm in lsu/ifu, we need to derive the number of beats from HBURST.
-  always_comb begin
-    case(HBURST)
+  //  HBURST[2:1] Beats
+  //  00          1
+  //  01          4
+  //  10          8
+  //  11          16
+  always_comb 
+    if (HBURST[2:1] == 2'b00) Threshold = 4'b0000;
+    else                      Threshold = (2 << HBURST[2:1]) - 1;
+/*    case(HBURST)
       0:        Threshold = 4'b0000;
       3:        Threshold = 4'b0011; // INCR4
       5:        Threshold = 4'b0111; // INCR8
       7:        Threshold = 4'b1111; // INCR16
       default:  Threshold = 4'b0000; // INCR without end.
     endcase
-  end
+  end */
 endmodule
diff --git a/testbench/tests.vh b/testbench/tests.vh
index f5e02290b..64b5ca59a 100644
--- a/testbench/tests.vh
+++ b/testbench/tests.vh
@@ -45,6 +45,7 @@ string tvpaths[] = '{
   string coverage64gc[] = '{
     `COVERAGE,
     "ieu",
+    "ebu",
     "csrwrites"
   };
 
diff --git a/tests/coverage/ebu.S b/tests/coverage/ebu.S
new file mode 100644
index 000000000..8c69f9d11
--- /dev/null
+++ b/tests/coverage/ebu.S
@@ -0,0 +1,45 @@
+///////////////////////////////////////////
+// ebu.S
+//
+// Written: David_Harris@hmc.edu 23 March 2023
+//
+// Purpose: Test coverage for EBU
+//
+// A component of the CORE-V-WALLY configurable RISC-V project.
+// 
+// Copyright (C) 2021-23 Harvey Mudd College & Oklahoma State University
+//
+// SPDX-License-Identifier: Apache-2.0 WITH SHL-2.1
+//
+// Licensed under the Solderpad Hardware License v 2.1 (the “License”); you may not use this file 
+// except in compliance with the License, or, at your option, the Apache License version 2.0. You 
+// may obtain a copy of the License at
+//
+// https://solderpad.org/licenses/SHL-2.1/
+//
+// Unless required by applicable law or agreed to in writing, any work distributed under the 
+// License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, 
+// either express or implied. See the License for the specific language governing permissions 
+// and limitations under the License.
+////////////////////////////////////////////////////////////////////////////////////////////////
+
+// load code to initalize stack, handle interrupts, terminate
+#include "WALLY-init-lib.h"
+
+main:
+
+    # Test clz with all bits being 0
+    li t0, 0
+    clz t1, t0
+    li t0, -1
+    clz t1, t0
+    li t0, 1
+    clz t1, t0
+
+    # Test forwarding from store conditional
+    lr.w t0, 0(a0)
+    sc.w t0, a1, 0(a0)
+    addi t0, t0, 1
+
+    j done
+