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diff --git a/src/intersim2/arbiters/tree_arb.cpp b/src/intersim2/arbiters/tree_arb.cpp
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+// $Id: tree_arb.cpp 5188 2012-08-30 00:31:31Z dub $
+
+/*
+ Copyright (c) 2007-2012, Trustees of The Leland Stanford Junior University
+ All rights reserved.
+
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted provided that the following conditions are met:
+
+ Redistributions of source code must retain the above copyright notice, this 
+ list of conditions and the following disclaimer.
+ Redistributions in binary form must reproduce the above copyright notice, this
+ list of conditions and the following disclaimer in the documentation and/or
+ other materials provided with the distribution.
+
+ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 
+ DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+// ----------------------------------------------------------------------
+//
+//  TreeArbiter
+//
+// ----------------------------------------------------------------------
+
+#include "tree_arb.hpp"
+#include <iostream>
+#include <sstream>
+
+using namespace std ;
+
+TreeArbiter::TreeArbiter( Module *parent, const string &name,
+			  int size, int groups, const string & arb_type ) 
+  : Arbiter( parent, name, size ) {
+  assert(size % groups == 0);
+  _group_arbiters.resize(groups);
+  _group_reqs.resize(groups, 0);
+  _group_size = size / groups;
+  for(int i = 0; i < groups; ++i) {
+    ostringstream group_arb_name;
+    group_arb_name << "group_arb" << i;
+    _group_arbiters[i] = Arbiter::NewArbiter(this, group_arb_name.str(), arb_type, _group_size);
+  }
+  _global_arbiter = Arbiter::NewArbiter(this, "global_arb", arb_type, groups);
+}
+
+TreeArbiter::~TreeArbiter() {
+  for(int i = 0; i < (int)_group_arbiters.size(); ++i) {
+    delete _group_arbiters[i];
+  }
+  delete _global_arbiter;
+}
+
+void TreeArbiter::PrintState() const  {
+  for(int i = 0; i < (int)_group_arbiters.size(); ++i) {
+    cout << "Group arbiter " << i << ":" << endl;
+    _group_arbiters[i]->PrintState();
+  }
+  cout << "Global arbiter:" << endl;
+  _global_arbiter->PrintState();
+}
+
+void TreeArbiter::UpdateState() {
+  if(_selected > -1) {
+    int last_winner = _global_arbiter->LastWinner();
+    assert(last_winner >= 0 && last_winner < (int)_group_arbiters.size());
+    _group_arbiters[last_winner]->UpdateState();
+    _global_arbiter->UpdateState();
+  }
+}
+
+void TreeArbiter::AddRequest( int input, int id, int pri )
+{
+  Arbiter::AddRequest(input, id, pri);
+  int group_index = input / _group_size;
+  _group_arbiters[group_index]->AddRequest( input % _group_size, id, pri );
+  ++_group_reqs[group_index];
+}
+
+int TreeArbiter::Arbitrate( int* id, int* pri ) {
+  if(!_num_reqs) {
+    return -1;
+  } 
+  for(int i = 0; i < (int)_group_arbiters.size(); ++i) {
+    if(_group_reqs[i]) {
+      int group_id, group_pri;
+      _group_arbiters[i]->Arbitrate(&group_id, &group_pri);
+      _global_arbiter->AddRequest(i, group_id, group_pri);
+    }
+  }
+  int group = _global_arbiter->Arbitrate(NULL, NULL);
+  assert(group >= 0 && group < (int)_group_arbiters.size());
+  int group_sel = _group_arbiters[group]->LastWinner();
+  assert(group_sel >= 0 && group_sel < _group_size);
+  _selected = group * _group_size + group_sel;
+  assert(_selected >= 0 && _selected < _size);
+  return Arbiter::Arbitrate(id, pri);
+}
+
+void TreeArbiter::Clear()
+{
+  if(!_num_reqs) {
+    return;
+  }
+  for(int i = 0; i < (int)_group_arbiters.size(); ++i) {
+    _group_arbiters[i]->Clear();
+    _group_reqs[i] = 0;
+  }
+  _global_arbiter->Clear();
+  Arbiter::Clear();
+}