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diff --git a/gcell/src/include/memory_barrier.h b/gcell/src/include/memory_barrier.h
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+++ b/gcell/src/include/memory_barrier.h
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+/* -*- c++ -*- */
+/*
+ * Copyright 2007 Free Software Foundation, Inc.
+ * 
+ * This file is part of GNU Radio
+ * 
+ * GNU Radio is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3, or (at your option)
+ * any later version.
+ * 
+ * GNU Radio is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef INCLUDED_MEMORY_BARRIER_H
+#define INCLUDED_MEMORY_BARRIER_H
+
+/*
+ * powerpc memory barriers
+ *
+ * The sync instruction guarantees that all memory accesses initiated
+ * by this processor have been performed (with respect to all other
+ * mechanisms that access memory).  The eieio instruction is a barrier
+ * providing an ordering (separately) for (a) cacheable stores and (b)
+ * loads and stores to non-cacheable memory (e.g. I/O devices).
+ *
+ * smp_mb() prevents loads and stores being reordered across this point.
+ * smp_rmb() prevents loads being reordered across this point.
+ * smp_wmb() prevents stores being reordered across this point.
+ *
+ * We have to use the sync instructions for smp_mb(), since lwsync
+ * doesn't order loads with respect to previous stores.  Lwsync is
+ * fine for smp_rmb(), though.  For smp_wmb(), we use eieio since it
+ * is only used to order updates to system memory.
+ *
+ * For details, see "PowerPC Virtual Environment Architecture, Book
+ * II".  Especially Chapter 1, "Storage Model" and Chapter 3, "Storage
+ * Control Instructions." (site:ibm.com)
+ */
+
+#include <ppu_intrinsics.h>
+
+static inline void smp_mb(void)
+{
+  __sync();
+}
+
+static inline void smp_rmb(void)
+{
+  __lwsync();
+}
+
+static inline void smp_wmb(void)
+{
+  __eieio();
+}
+
+
+#endif /* INCLUDED_MEMORY_BARRIER_H */