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diff --git a/nuttx/drivers/power/pm_changestate.c b/nuttx/drivers/power/pm_changestate.c
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+++ b/nuttx/drivers/power/pm_changestate.c
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+/****************************************************************************
+ * drivers/power/pm_changestate.c
+ *
+ *   Copyright (C) 2011-2012 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. 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.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * 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.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <nuttx/power/pm.h>
+#include <arch/irq.h>
+
+#include "pm_internal.h"
+
+#ifdef CONFIG_PM
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Data
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: pm_prepall
+ *
+ * Description:
+ *   Prepare every driver for the state change.
+ *
+ * Input Parameters:
+ *   newstate - Identifies the new PM state
+ *
+ * Returned Value:
+ *   0 (OK) means that the callback function for all registered drivers
+ *   returned OK (meaning that they accept the state change).  Non-zero
+ *   means that one of the drivers refused the state change.  In this case,
+ *   the system will revert to the preceding state.
+ *
+ * Assumptions:
+ *   Interrupts are disabled.
+ *
+ ****************************************************************************/
+
+static int pm_prepall(enum pm_state_e newstate)
+{
+  FAR sq_entry_t *entry;
+  int ret = OK;
+
+  /* Visit each registered callback structure. */
+
+  for (entry = sq_peek(&g_pmglobals.registry);
+       entry && ret == OK;
+       entry = sq_next(entry))
+    {
+      /* Is the prepare callback supported? */
+
+      FAR struct pm_callback_s *cb = (FAR struct pm_callback_s *)entry;
+      if (cb->prepare)
+        {
+          /* Yes.. prepare the driver */
+
+          ret = cb->prepare(cb, newstate);
+        }
+    }
+
+  return ret;
+}
+
+/****************************************************************************
+ * Name: pm_changeall
+ *
+ * Description:
+ *   Inform all drivers of the state change.
+ *
+ * Input Parameters:
+ *   newstate - Identifies the new PM state
+ *
+ * Returned Value:
+ *   None
+ *
+ * Assumptions:
+ *   Interrupts are disabled.
+ *
+ ****************************************************************************/
+
+static inline void pm_changeall(enum pm_state_e newstate)
+{
+  FAR sq_entry_t *entry;
+
+  /* Visit each registered callback structure. */
+
+  for (entry = sq_peek(&g_pmglobals.registry); entry; entry = sq_next(entry))
+    {
+      /* Is the notification callback supported? */
+
+      FAR struct pm_callback_s *cb = (FAR struct pm_callback_s *)entry;
+      if (cb->notify)
+        {
+          /* Yes.. notify the driver */
+
+          cb->notify(cb, newstate);
+        }
+    }
+}
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: pm_changestate
+ *
+ * Description:
+ *   This function is used by platform-specific power management logic.  It
+ *   will announce the power management power management state change to all
+ *   drivers that have registered for power management event callbacks.
+ *
+ * Input Parameters:
+ *   newstate - Identifies the new PM state
+ *
+ * Returned Value:
+ *   0 (OK) means that the callback function for all registered drivers
+ *   returned OK (meaning that they accept the state change).  Non-zero
+ *   means that one of the drivers refused the state change.  In this case,
+ *   the system will revert to the preceding state.
+ *
+ * Assumptions:
+ *   It is assumed that interrupts are disabled when this function is
+ *   called.  This function is probably called from the IDLE loop... the
+ *   lowest priority task in the system.  Changing driver power management
+ *   states may result in renewed system activity and, as a result, can
+ *   suspend the IDLE thread before it completes the entire state change
+ *   unless interrupts are disabled throughout the state change.
+ *
+ ****************************************************************************/
+
+int pm_changestate(enum pm_state_e newstate)
+{
+  irqstate_t flags;
+  int ret;
+
+  /* Disable interrupts throught this operation... changing driver states
+   * could cause additional driver activity that might interfere with the
+   * state change.  When the state change is complete, interrupts will be
+   * re-enabled.
+   */
+
+  flags = irqsave();
+
+  /* First, prepare the drivers for the state change.  In this phase,
+   * drivers may refuse the state state change.
+   */
+
+  ret = pm_prepall(newstate);
+  if (ret != OK)
+    {
+      /* One or more drivers is not ready for this state change.  Revert to
+       * the preceding state.
+       */
+
+      newstate = g_pmglobals.state;
+      (void)pm_prepall(newstate);
+    }
+
+  /* All drivers have agreed to the state change (or, one or more have
+   * disagreed and the state has been reverted).  Set the new state.
+   */
+
+  pm_changeall(newstate);
+  g_pmglobals.state = newstate;
+
+  /* Restore the interrupt state */
+
+  irqrestore(flags);
+  return ret;
+}
+
+#endif /* CONFIG_PM */