Adding base class for LoRaWAN interfaces

All network interfaces for LoRaWAN protocol must implement this
class. In order to be compatible with Mbed-OS applications, any
implementation of this class must use the data structures and
Mbed-OS timers provided.

lorawan_data_structures may look repetitive but this is essential
as we have a plan to use a reference implementation for LoRaWAN mac
layer from Semtech. Some of the data structures provide seemless
transition from semtech implementation (as MAC layer) to the Mbed-OS
control layers above.

features/lorawan/lorastack is the placeholder for future items like mac and
phy layers. system/ will contain all the common bits.

Author: Hasnain Virk

features/lorawan/system/LoRaWANTimer.cpp

@@ -0,0 +1,84 @@
+/**
+ / _____)             _              | |
+( (____  _____ ____ _| |_ _____  ____| |__
+ \____ \| ___ |    (_   _) ___ |/ ___)  _ \
+ _____) ) ____| | | || |_| ____( (___| | | |
+(______/|_____)_|_|_| \__)_____)\____)_| |_|
+    (C)2013 Semtech
+
+Description: Timer objects and scheduling management
+
+License: Revised BSD License, see LICENSE.TXT file include in the project
+
+Maintainer: Miguel Luis and Gregory Cristian
+
+
+Copyright (c) 2017, Arm Limited and affiliates.
+
+SPDX-License-Identifier: BSD-3-Clause
+*/
+
+#include "lorawan/system/LoRaWANTimer.h"
+
+static mbed::Timer TimeCounter;
+static mbed::Ticker LoadTimeCounter;
+
+volatile uint32_t CurrentTime = 0;
+
+void TimerResetTimeCounter( void )
+{
+    CurrentTime = CurrentTime + TimeCounter.read_us( ) / 1000;
+    TimeCounter.reset( );
+    TimeCounter.start( );
+}
+
+void TimerTimeCounterInit( void )
+{
+    TimeCounter.start( );
+    LoadTimeCounter.attach( mbed::callback( &TimerResetTimeCounter ), 10 );
+}
+
+TimerTime_t TimerGetCurrentTime( void )
+{
+    CurrentTime += TimeCounter.read_us( ) / 1000;
+    TimeCounter.reset( );
+    TimeCounter.start( );
+    return ( ( TimerTime_t )CurrentTime );
+}
+
+TimerTime_t TimerGetElapsedTime( TimerTime_t savedTime )
+{
+    CurrentTime += TimeCounter.read_us( ) / 1000;
+    TimeCounter.reset( );
+    TimeCounter.start( );
+    return ( TimerTime_t )( CurrentTime - savedTime );
+}
+
+TimerTime_t TimerGetFutureTime( TimerTime_t eventInFuture )
+{
+    CurrentTime += TimeCounter.read_us( ) / 1000;
+    TimeCounter.reset( );
+    TimeCounter.start( );
+    return ( TimerTime_t )( CurrentTime + eventInFuture );
+}
+
+void TimerInit( TimerEvent_t *obj, void ( *callback )( void ) )
+{
+    obj->value = 0;
+    obj->Callback = callback;
+}
+
+void TimerStart( TimerEvent_t *obj )
+{
+    obj->Timer.attach_us( mbed::callback( obj->Callback ), obj->value * 1000 );
+}
+
+void TimerStop( TimerEvent_t *obj )
+{
+    obj->Timer.detach( );
+}
+
+void TimerSetValue( TimerEvent_t *obj, uint32_t value )
+{
+    obj->value = value;
+}

features/lorawan/system/LoRaWANTimer.h

@@ -0,0 +1,107 @@
+/**
+ / _____)             _              | |
+( (____  _____ ____ _| |_ _____  ____| |__
+ \____ \| ___ |    (_   _) ___ |/ ___)  _ \
+ _____) ) ____| | | || |_| ____( (___| | | |
+(______/|_____)_|_|_| \__)_____)\____)_| |_|
+    (C)2013 Semtech
+
+Description: Timer objects and scheduling management
+
+License: Revised BSD License, see LICENSE.TXT file include in the project
+
+Maintainer: Miguel Luis and Gregory Cristian
+
+
+Copyright (c) 2017, Arm Limited and affiliates.
+
+SPDX-License-Identifier: BSD-3-Clause
+*/
+
+#ifndef MBED_LORAWAN_SYS_TIMER_H__
+#define MBED_LORAWAN_SYS_TIMER_H__
+#include "drivers/Timer.h"
+#include "drivers/Ticker.h"
+#include "lorawan/system/lorawan_data_structures.h"
+
+/*!
+ * \brief Timer object description
+ */
+typedef struct TimerEvent_s
+{
+    uint32_t value;
+    void ( *Callback )( void );
+    mbed::Ticker Timer;
+}TimerEvent_t;
+
+/*!
+ * \brief Initializes the timer used to get the current time.
+ *
+ * \remark The current time corresponds to the time since system startup.
+ */
+void TimerTimeCounterInit( void );
+
+/*!
+ * \brief Initializes the timer object.
+ *
+ * \remark The TimerSetValue function must be called before starting the timer.
+ *         This function initializes the timestamp and reloads the value at 0.
+ *
+ * \param [in] obj          The structure containing the timer object parameters.
+ * \param [in] callback     The function callback called at the end of the timeout.
+ */
+void TimerInit( TimerEvent_t *obj, void ( *callback )( void ) );
+
+/*!
+ * \brief Starts and adds the timer object to the list of timer events.
+ *
+ * \param [in] obj The structure containing the timer object parameters.
+ */
+void TimerStart( TimerEvent_t *obj );
+
+/*!
+ * \brief Stops and removes the timer object from the list of timer events.
+ *
+ * \param [in] obj The structure containing the timer object parameters.
+ */
+void TimerStop( TimerEvent_t *obj );
+
+/*!
+ * \brief Resets the timer object.
+ *
+ * \param [in] obj The structure containing the timer object parameters.
+ */
+void TimerReset( TimerEvent_t *obj );
+
+/*!
+ * \brief Set a new timeout value.
+ *
+ * \param [in] obj   The structure containing the timer object parameters.
+ * \param [in] value The new timeout value.
+ */
+void TimerSetValue( TimerEvent_t *obj, uint32_t value );
+
+/*!
+ * \brief Read the current time.
+ *
+ * \retval time The current time.
+ */
+TimerTime_t TimerGetCurrentTime( void );
+
+/*!
+ * \brief Return the time elapsed since a fixed moment in time.
+ *
+ * \param [in] savedTime    The fixed moment in time.
+ * \retval time             The elapsed time.
+ */
+TimerTime_t TimerGetElapsedTime( TimerTime_t savedTime );
+
+/*!
+ * \brief Return the time elapsed since a fixed moment in time.
+ *
+ * \param [in] eventInFuture    The fixed moment in the future.
+ * \retval time             The difference between now and a future event.
+ */
+TimerTime_t TimerGetFutureTime( TimerTime_t eventInFuture );
+
+#endif // MBED_LORAWAN_SYS_TIMER_H__