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diff --git a/nuttx/sched/usleep.c b/nuttx/sched/usleep.c
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+/****************************************************************************
+ * sched/usleep.c
+ *
+ *   Copyright (C) 2007, 2009, 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 <sys/types.h>
+#include <unistd.h>
+#include <signal.h>
+#include <assert.h>
+#include <errno.h>
+
+/****************************************************************************
+ * Definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Type Declarations
+ ****************************************************************************/
+
+/****************************************************************************
+ * Global Variables
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Variables
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: usleep
+ *
+ * Description:
+ *   The usleep() function will cause the calling thread to be suspended
+ *   from execution until either the number of real-time microseconds
+ *   specified by the argument 'usec' has elapsed or a signal is delivered
+ *   to the calling thread. The suspension time may be longer than requested
+ *   due to the scheduling of other activity by the system.
+ *
+ *   The 'usec' argument must be less than 1,000,000. If the value of
+ *   'usec' is 0, then the call has no effect.
+ *
+ *   If a SIGALRM signal is generated for the calling process during
+ *   execution of usleep() and if the SIGALRM signal is being ignored or
+ *   blocked from delivery, it is unspecified whether usleep() returns
+ *   when the SIGALRM signal is scheduled. If the signal is being blocked, it
+ *   is also unspecified whether it remains pending after usleep() returns or
+ *   it is discarded.
+ *
+ *   If a SIGALRM signal is generated for the calling process during
+ *   execution of usleep(), except as a result of a prior call to alarm(),
+ *   and if the SIGALRM signal is not being ignored or blocked from delivery,
+ *   it is unspecified whether that signal has any effect other than causing
+ *   usleep() to return.
+ *
+ *   If a signal-catching function interrupts usleep() and examines or changes
+ *   either the time a SIGALRM is scheduled to be generated, the action
+ *   associated with the SIGALRM signal, or whether the SIGALRM signal is
+ *   blocked from delivery, the results are unspecified.
+ *
+ *   If a signal-catching function interrupts usleep() and calls siglongjmp()
+ *   or longjmp() to restore an environment saved prior to the usleep() call,
+ *   the action associated with the SIGALRM signal and the time at which a
+ *   SIGALRM signal is scheduled to be generated are unspecified. It is also
+ *   unspecified whether the SIGALRM signal is blocked, unless the process'
+ *   signal mask is restored as part of the environment.
+ *
+ *   Implementations may place limitations on the granularity of timer values.
+ *   For each interval timer, if the requested timer value requires a finer
+ *   granularity than the implementation supports, the actual timer value will
+ *   be rounded up to the next supported value. 
+ *
+ *   Interactions between usleep() and any of the following are unspecified:
+ *
+ *   nanosleep(), setitimer(), timer_create(), timer_delete(), timer_getoverrun(),
+ *   timer_gettime(), timer_settime(), ualarm(), sleep()
+
+ * Parameters:
+ *   usec - the number of microseconds to wait.
+ *
+ * Returned Value:
+ *   On successful completion, usleep() returns 0. Otherwise, it returns -1
+ *   and sets errno to indicate the error. 
+ *
+ * Assumptions:
+ *
+ ****************************************************************************/
+
+int usleep(useconds_t usec)
+{
+  sigset_t set;
+  struct timespec ts;
+  struct siginfo value;
+  int errval;
+  int ret = 0;
+
+  if (usec)
+    {
+      /* Set up for the sleep.  Using the empty set means that we are not
+       * waiting for any particualar signal.  However, any unmasked signal
+       * can still awaken sigtimedwait().
+       */
+
+      (void)sigemptyset(&set);
+      ts.tv_sec  = usec / 1000000;
+      ts.tv_nsec = (usec % 1000000) * 1000;
+
+      /* usleep is a simple application of sigtimedwait. */
+
+      ret = sigtimedwait(&set, &value, &ts);
+
+      /* sigtimedwait() cannot succeed.  It should always return error with
+       * either (1) EAGAIN meaning that the timeout occurred, or (2) EINTR
+       * meaning that some other unblocked signal was caught.
+       */
+
+      errval = errno;
+      DEBUGASSERT(ret < 0 && (errval == EAGAIN || errval == EINTR));
+      if (errval == EAGAIN)
+        {
+          /* The timeout "error" is the normal, successful result */
+
+          ret = 0;
+        }
+    }
+
+  return ret;
+}