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diff --git a/nuttx/drivers/power/pm_checkstate.c b/nuttx/drivers/power/pm_checkstate.c
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+++ b/nuttx/drivers/power/pm_checkstate.c
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+/****************************************************************************
+ * drivers/power/pm_checkstate.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 <nuttx/clock.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
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: pm_checkstate
+ *
+ * Description:
+ *   This function is called from the MCU-specific IDLE loop to monitor the
+ *   the power management conditions.  This function returns the "recommended"
+ *   power management state based on the PM configuration and activity
+ *   reported in the last sampling periods.  The power management state is
+ *   not automatically changed, however.  The IDLE loop must call
+ *   pm_changestate() in order to make the state change.
+ *
+ *   These two steps are separated because the plaform-specific IDLE loop may
+ *   have additional situational information that is not available to the
+ *   the PM sub-system.  For example, the IDLE loop may know that the
+ *   battery charge level is very low and may force lower power states
+ *   even if there is activity.
+ *
+ *   NOTE: That these two steps are separated in time and, hence, the IDLE
+ *   loop could be suspended for a long period of time between calling
+ *   pm_checkstate() and pm_changestate().  The IDLE loop may need to make
+ *   these calls atomic by either disabling interrupts until the state change
+ *   is completed.
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value:
+ *   The recommended power management state.
+ *
+ ****************************************************************************/
+
+enum pm_state_e pm_checkstate(void)
+{
+  uint32_t now;
+  irqstate_t flags;
+
+  /* Check for the end of the current time slice.  This must be performed
+   * with interrupts disabled so that it does not conflict with the similar
+   * logic in pm_activity().
+   */
+
+  flags = irqsave();
+
+  /* Check the elapsed time.  In periods of low activity, time slicing is
+   * controlled by IDLE loop polling; in periods of higher activity, time
+   * slicing is controlled by driver activity.  In either case, the duration
+   * of the time slice is only approximate; during times of heavy activity,
+   * time slices may be become longer and the activity level may be over-
+   * estimated.
+   */
+
+   now = clock_systimer();
+   if (now - g_pmglobals.stime >= TIME_SLICE_TICKS)
+    {
+       int16_t accum;
+
+       /* Sample the count, reset the time and count, and assess the PM
+        * state.  This is an atomic operation because interrupts are
+        * still disabled.
+        */
+
+       accum             = g_pmglobals.accum;
+       g_pmglobals.stime = now;
+       g_pmglobals.accum = 0;
+
+       /* Reassessing the PM state may require some computation.  However,
+        * the work will actually be performed on a worker thread at a user-
+        * controlled priority.
+        */
+
+       (void)pm_update(accum);
+    }
+  irqrestore(flags);
+
+  /* Return the recommended state.  Assuming that we are called from the
+   * IDLE thread at the lowest priority level, any updates scheduled on the
+   * worker thread above should have already been peformed and the recommended
+   * state should be current:
+   */
+
+  return g_pmglobals.recommended;
+}
+
+#endif /* CONFIG_PM */