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diff --git a/nuttx/configs/vsn/src/rtac.c b/nuttx/configs/vsn/src/rtac.c
new file mode 100644
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+++ b/nuttx/configs/vsn/src/rtac.c
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+/****************************************************************************
+ * config/vsn/src/rtac.c
+ * arch/arm/src/board/rtac.c
+ *
+ *   Copyright (C) 2011 Uros Platise. All rights reserved.
+ *
+ *   Authors: Uros Platise <uros.platise@isotel.eu>
+ *
+ * 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.
+ *
+ ****************************************************************************/
+
+/** \file
+ *  \author Uros Platise
+ *  \brief Real Time Alarm Clock
+ * 
+ * Implementation of the Real-Time Alarm Clock as per SNP Specifications.
+ * It provides real-time and phase controlled timer module while it 
+ * cooperates with hardware RTC for low-power operation.
+ * 
+ * It provides a replacement for a system 32-bit UTC time/date counter.
+ * 
+ * It runs at maximum STM32 allowed precision of 16384 Hz, providing 
+ * resolution of 61 us, required by the Sensor Network Protocol.
+ */
+
+/****************************************************************************
+ * Definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/** Execute from a group of events
+ **/
+int rtac_execg(int group)
+{
+    // called by each thread to spawn its apps given by its ID or group ID of
+    // multiple threads, when group parameter is set.
+}
+
+
+/** Wait and execute from a group of events
+ **/
+int rtac_waitg(int group, int time)
+{
+    // blocking variant of rtac_exec with timeout if specified
+}
+
+
+/** Power optimization of base systick timer
+ * 
+ * 1. Simple method to skip wake-ups:
+ *  - ask timers about the min. period, which is Ns * systick
+ *  - set the preload register with floor(Ns) * DEFAULT_PRELOAD
+ *  - on wake-up call routines Ns times.
+ * 
+ * 2. If intermediate ISR occuried then:
+ *  - check how many periods have passed by reading the counter: Np
+ *  - set the new counter value as (counter % DEFAULT_PRELOAD)
+ *  - call timer routines Np times; the next call is as usual, starting
+ *    at 1. point above
+ * 
+ * This is okay if ISR's do not read timers, if they read timers then:
+ *  - on ISR wake-up the code described under 2. must be called first
+ *    (on wake-up from IDLE)
+ * 
+ * BUT: the problem is that SYSTICK does not run in Stop mode but RTC
+ *   only, so it might be better to replace SYSTICK with RTAC (this
+ *   module) and do the job above, permitting ultra low power modes of
+ *   25 uA or further down to 5 uA.
+ */