From d2da33e4b162fe862f0cb057ccfe55a979a1b251 Mon Sep 17 00:00:00 2001
From: "Wesley W. Terpstra" <wesley@sifive.com>
Date: Sat, 11 Mar 2017 02:53:11 -0800
Subject: [PATCH] Fuzzer: use different LFSR seeds based on simulator seed

---
 src/main/scala/uncore/tilelink2/Fuzzer.scala | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/src/main/scala/uncore/tilelink2/Fuzzer.scala b/src/main/scala/uncore/tilelink2/Fuzzer.scala
index 724015f7..73b4a032 100644
--- a/src/main/scala/uncore/tilelink2/Fuzzer.scala
+++ b/src/main/scala/uncore/tilelink2/Fuzzer.scala
@@ -34,16 +34,11 @@ class IDMapGenerator(numIds: Int) extends Module {
 
 object LFSR64
 { 
-  private var counter = 0 
-  private def next: Int = {
-    counter += 1
-    counter
-  }
-  
-  def apply(increment: Bool = Bool(true), seed: Int = next): UInt =
+  def apply(increment: Bool = Bool(true)): UInt =
   { 
     val wide = 64
-    val lfsr = RegInit(UInt((seed * 0xDEADBEEFCAFEBAB1L) >>> 1, width = wide))
+    val undef = Reg(UInt(width = wide)) // random value based on simulation seed
+    val lfsr = RegInit(Mux(undef === UInt(0), UInt(1), undef))
     val xor = lfsr(0) ^ lfsr(1) ^ lfsr(3) ^ lfsr(4)
     when (increment) { lfsr := Cat(xor, lfsr(wide-1,1)) }
     lfsr