include/event_groups.h

/*
 * FreeRTOS Kernel V10.3.1
 * Copyright (C) 2020 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * http://www.FreeRTOS.org
 * http://aws.amazon.com/freertos
 *
 * 1 tab == 4 spaces!
 */

#ifndef EVENT_GROUPS_H
#define EVENT_GROUPS_H

#ifndef INC_FREERTOS_H
	#error "include FreeRTOS.h" must appear in source files before "include event_groups.h"
#endif

/* FreeRTOS includes. */
#include "timers.h"

#ifdef __cplusplus
extern "C" {
#endif

/**
 * An event group is a collection of bits to which an application can assign a
 * meaning.  For example, an application may create an event group to convey
 * the status of various CAN bus related events in which bit 0 might mean "A CAN
 * message has been received and is ready for processing", bit 1 might mean "The
 * application has queued a message that is ready for sending onto the CAN
 * network", and bit 2 might mean "It is time to send a SYNC message onto the
 * CAN network" etc.  A task can then test the bit values to see which events
 * are active, and optionally enter the Blocked state to wait for a specified
 * bit or a group of specified bits to be active.  To continue the CAN bus
 * example, a CAN controlling task can enter the Blocked state (and therefore
 * not consume any processing time) until either bit 0, bit 1 or bit 2 are
 * active, at which time the bit that was actually active would inform the task
 * which action it had to take (process a received message, send a message, or
 * send a SYNC).
 *
 * The event groups implementation contains intelligence to avoid race
 * conditions that would otherwise occur were an application to use a simple
 * variable for the same purpose.  This is particularly important with respect
 * to when a bit within an event group is to be cleared, and when bits have to
 * be set and then tested atomically - as is the case where event groups are
 * used to create a synchronisation point between multiple tasks (a
 * 'rendezvous').
 *
 * \defgroup EventGroup
 */



/**
 * event_groups.h
 *
 * Type by which event groups are referenced.  For example, a call to
 * xEventGroupCreate() returns an EventGroupHandle_t variable that can then
 * be used as a parameter to other event group functions.
 *
 * \defgroup EventGroupHandle_t EventGroupHandle_t
 * \ingroup EventGroup
 */
struct EventGroupDef_t;
typedef struct EventGroupDef_t * EventGroupHandle_t;

/*
 * The type that holds event bits always matches TickType_t - therefore the
 * number of bits it holds is set by configUSE_16_BIT_TICKS (16 bits if set to 1,
 * 32 bits if set to 0.
 *
 * \defgroup EventBits_t EventBits_t
 * \ingroup EventGroup
 */
typedef TickType_t EventBits_t;

/**
 * event_groups.h
 *<pre>
 EventGroupHandle_t xEventGroupCreate( void );
 </pre>
 *
 * Create a new event group.
 *
 * Internally, within the FreeRTOS implementation, event groups use a [small]
 * block of memory, in which the event group's structure is stored.  If an event
 * groups is created using xEventGropuCreate() then the required memory is
 * automatically dynamically allocated inside the xEventGroupCreate() function.
 * (see http://www.freertos.org/a00111.html).  If an event group is created
 * using xEventGropuCreateStatic() then the application writer must instead
 * provide the memory that will get used by the event group.
 * xEventGroupCreateStatic() therefore allows an event group to be created
 * without using any dynamic memory allocation.
 *
 * Although event groups are not related to ticks, for internal implementation
 * reasons the number of bits available for use in an event group is dependent
 * on the configUSE_16_BIT_TICKS setting in FreeRTOSConfig.h.  If
 * configUSE_16_BIT_TICKS is 1 then each event group contains 8 usable bits (bit
 * 0 to bit 7).  If configUSE_16_BIT_TICKS is set to 0 then each event group has
 * 24 usable bits (bit 0 to bit 23).  The EventBits_t type is used to store
 * event bits within an event group.
 *
 * @return If the event group was created then a handle to the event group is
 * returned.  If there was insufficient FreeRTOS heap available to create the
 * event group then NULL is returned.  See http://www.freertos.org/a00111.html
 *
 * Example usage:
   <pre>
	// Declare a variable to hold the created event group.
	EventGroupHandle_t xCreatedEventGroup;

	// Attempt to create the event group.
	xCreatedEventGroup = xEventGroupCreate();

	// Was the event group created successfully?
	if( xCreatedEventGroup == NULL )
	{
		// The event group was not created because there was insufficient
		// FreeRTOS heap available.
	}
	else
	{
		// The event group was created.
	}
   </pre>
 * \defgroup xEventGroupCreate xEventGroupCreate
 * \ingroup EventGroup
 */
#if( configSUPPORT_DYNAMIC_ALLOCATION == 1 )
	EventGroupHandle_t xEventGroupCreate( void ) PRIVILEGED_FUNCTION;
#endif

/**
 * event_groups.h
 *<pre>
 EventGroupHandle_t xEventGroupCreateStatic( EventGroupHandle_t * pxEventGroupBuffer );
 </pre>
 *
 * Create a new event group.
 *
 * Internally, within the FreeRTOS implementation, event groups use a [small]
 * block of memory, in which the event group's structure is stored.  If an event
 * groups is created using xEventGropuCreate() then the required memory is
 * automatically dynamically allocated inside the xEventGroupCreate() function.
 * (see http://www.freertos.org/a00111.html).  If an event group is created
 * using xEventGropuCreateStatic() then the application writer must instead
 * provide the memory that will get used by the event group.
 * xEventGroupCreateStatic() therefore allows an event group to be created
 * without using any dynamic memory allocation.
 *
 * Although event groups are not related to ticks, for internal implementation
 * reasons the number of bits available for use in an event group is dependent
 * on the configUSE_16_BIT_TICKS setting in FreeRTOSConfig.h.  If
 * configUSE_16_BIT_TICKS is 1 then each event group contains 8 usable bits (bit
 * 0 to bit 7).  If configUSE_16_BIT_TICKS is set to 0 then each event group has
 * 24 usable bits (bit 0 to bit 23).  The EventBits_t type is used to store
 * event bits within an event group.
 *
 * @param pxEventGroupBuffer pxEventGroupBuffer must point to a variable of type
 * StaticEventGroup_t, which will be then be used to hold the event group's data
 * structures, removing the need for the memory to be allocated dynamically.
 *
 * @return If the event group was created then a handle to the event group is
 * returned.  If pxEventGroupBuffer was NULL then NULL is returned.
 *
 * Example usage:
   <pre>
	// StaticEventGroup_t is a publicly accessible structure that has the same
	// size and alignment requirements as the real event group structure.  It is
	// provided as a mechanism for applications to know the size of the event
	// group (which is dependent on the architecture and configuration file
	// settings) without breaking the strict data hiding policy by exposing the
	// real event group internals.  This StaticEventGroup_t variable is passed
	// into the xSemaphoreCreateEventGroupStatic() function and is used to store
	// the event group's data structures
	StaticEventGroup_t xEventGroupBuffer;

	// Create the event group without dynamically allocating any memory.
	xEventGroup = xEventGroupCreateStatic( &xEventGroupBuffer );
   </pre>
 */
#if( configSUPPORT_STATIC_ALLOCATION == 1 )
	EventGroupHandle_t xEventGroupCreateStatic( StaticEventGroup_t *pxEventGroupBuffer ) PRIVILEGED_FUNCTION;
#endif

/**
 * event_groups.h
 *<pre>
	EventBits_t xEventGroupWaitBits( 	EventGroupHandle_t xEventGroup,
										const EventBits_t uxBitsToWaitFor,
										const BaseType_t xClearOnExit,
										const BaseType_t xWaitForAllBits,
										const TickType_t xTicksToWait );
 </pre>
 *
 * [Potentially] block to wait for one or more bits to be set within a
 * previously created event group.
 *
 * This function cannot be called from an interrupt.
 *
 * @param xEventGroup The event group in which the bits are being tested.  The
 * event group must have previously been created using a call to
 * xEventGroupCreate().
 *
 * @param uxBitsToWaitFor A bitwise value that indicates the bit or bits to test
 * inside the event group.  For example, to wait for bit 0 and/or bit 2 set
 * uxBitsToWaitFor to 0x05.  To wait for bits 0 and/or bit 1 and/or bit 2 set
 * uxBitsToWaitFor to 0x07.  Etc.
 *
 * @param xClearOnExit If xClearOnExit is set to pdTRUE then any bits within
 * uxBitsToWaitFor that are set within the event group will be cleared before
 * xEventGroupWaitBits() returns if the wait condition was met (if the function
 * returns for a reason other than a timeout).  If xClearOnExit is set to
 * pdFALSE then the bits set in the event group are not altered when the call to
 * xEventGroupWaitBits() returns.
 *
 * @param xWaitForAllBits If xWaitForAllBits is set to pdTRUE then
 * xEventGroupWaitBits() will return when either all the bits in uxBitsToWaitFor
 * are set or the specified block time expires.  If xWaitForAllBits is set to
 * pdFALSE then xEventGroupWaitBits() will return when any one of the bits set
 * in uxBitsToWaitFor is set or the specified block time expires.  The block
 * time is specified by the xTicksToWait parameter.
 *
 * @param xTicksToWait The maximum amount of time (specified in 'ticks') to wait
 * for one/all (depending on the xWaitForAllBits value) of the bits specified by
 * uxBitsToWaitFor to become set.
 *
 * @return The value of the event group at the time either the bits being waited
 * for became set, or the block time expired.  Test the return value to know
 * which bits were set.  If xEventGroupWaitBits() returned because its timeout
 * expired then not all the bits being waited for will be set.  If
 * xEventGroupWaitBits() returned because the bits it was waiting for were set
 * then the returned value is the event group value before any bits were
 * automatically cleared in the case that xClearOnExit parameter was set to
 * pdTRUE.
 *
 * Example usage:
   <pre>
   #define BIT_0	( 1 << 0 )
   #define BIT_4	( 1 << 4 )

   void aFunction( EventGroupHandle_t xEventGroup )
   {
   EventBits_t uxBits;
   const TickType_t xTicksToWait = 100 / portTICK_PERIOD_MS;

		// Wait a maximum of 100ms for either bit 0 or bit 4 to be set within
		// the event group.  Clear the bits before exiting.
		uxBits = xEventGroupWaitBits(
					xEventGroup,	// The event group being tested.
					BIT_0 | BIT_4,	// The bits within the event group to wait for.
					pdTRUE,			// BIT_0 and BIT_4 should be cleared before returning.
					pdFALSE,		// Don't wait for both bits, either bit will do.
					xTicksToWait );	// Wait a maximum of 100ms for either bit to be set.

		if( ( uxBits & ( BIT_0 | BIT_4 ) ) == ( BIT_0 | BIT_4 ) )
		{
			// xEventGroupWaitBits() returned because both bits were set.
		}
		else if( ( uxBits & BIT_0 ) != 0 )
		{
			// xEventGroupWaitBits() returned because just BIT_0 was set.
		}
		else if( ( uxBits & BIT_4 ) != 0 )
		{
			// xEventGroupWaitBits() returned because just BIT_4 was set.
		}
		else
		{
			// xEventGroupWaitBits() returned because xTicksToWait ticks passed
			// without either BIT_0 or BIT_4 becoming set.
		}
   }
   </pre>
 * \defgroup xEventGroupWaitBits xEventGroupWaitBits
 * \ingroup EventGroup
 */
EventBits_t xEventGroupWaitBits( EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToWaitFor, const BaseType_t xClearOnExit, const BaseType_t xWaitForAllBits, TickType_t xTicksToWait ) PRIVILEGED_FUNCTION;

/**
 * event_groups.h
 *<pre>
	EventBits_t xEventGroupClearBits( EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToClear );
 </pre>
 *
 * Clear bits within an event group.  This function cannot be called from an
 * interrupt.
 *
 * @param xEventGroup The event group in which the bits are to be cleared.
 *
 * @param uxBitsToClear A bitwise value that indicates the bit or bits to clear
 * in the event group.  For example, to clear bit 3 only, set uxBitsToClear to
 * 0x08.  To clear bit 3 and bit 0 set uxBitsToClear to 0x09.
 *
 * @return The value of the event group before the specified bits were cleared.
 *
 * Example usage:
   <pre>
   #define BIT_0	( 1 << 0 )
   #define BIT_4	( 1 << 4 )

   void aFunction( EventGroupHandle_t xEventGroup )
   {
   EventBits_t uxBits;

		// Clear bit 0 and bit 4 in xEventGroup.
		uxBits = xEventGroupClearBits(
								xEventGroup,	// The event group being updated.
								BIT_0 | BIT_4 );// The bits being cleared.

		if( ( uxBits & ( BIT_0 | BIT_4 ) ) == ( BIT_0 | BIT_4 ) )
		{
			// Both bit 0 and bit 4 were set before xEventGroupClearBits() was
			// called.  Both will now be clear (not set).
		}
		else if( ( uxBits & BIT_0 ) != 0 )
		{
			// Bit 0 was set before xEventGroupClearBits() was called.  It will
			// now be clear.
		}
		else if( ( uxBits & BIT_4 ) != 0 )
		{
			// Bit 4 was set before xEventGroupClearBits() was called.  It will
			// now be clear.
		}
		else
		{
			// Neither bit 0 nor bit 4 were set in the first place.
		}
   }
   </pre>
 * \defgroup xEventGroupClearBits xEventGroupClearBits
 * \ingroup EventGroup
 */
EventBits_t xEventGroupClearBits( EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToClear ) PRIVILEGED_FUNCTION;

/**
 * event_groups.h
 *<pre>
	BaseType_t xEventGroupClearBitsFromISR( EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToSet );
 </pre>
 *
 * A version of xEventGroupClearBits() that can be called from an interrupt.
 *
 * Setting bits in an event group is not a deterministic operation because there
 * are an unknown number of tasks that may be waiting for the bit or bits being
 * set.  FreeRTOS does not allow nondeterministic operations to be performed
 * while interrupts are disabled, so protects event groups that are accessed
 * from tasks by suspending the scheduler rather than disabling interrupts.  As
 * a result event groups cannot be accessed directly from an interrupt service
 * routine.  Therefore xEventGroupClearBitsFromISR() sends a message to the
 * timer task to have the clear operation performed in the context of the timer
 * task.
 *
 * @param xEventGroup The event group in which the bits are to be cleared.
 *
 * @param uxBitsToClear A bitwise value that indicates the bit or bits to clear.
 * For example, to clear bit 3 only, set uxBitsToClear to 0x08.  To clear bit 3
 * and bit 0 set uxBitsToClear to 0x09.
 *
 * @return If the request to execute the function was posted successfully then
 * pdPASS is returned, otherwise pdFALSE is returned.  pdFALSE will be returned
 * if the timer service queue was full.
 *
 * Example usage:
   <pre>
   #define BIT_0	( 1 << 0 )
   #define BIT_4	( 1 << 4 )

   // An event group which it is assumed has already been created by a call to
   // xEventGroupCreate().
   EventGroupHandle_t xEventGroup;

   void anInterruptHandler( void )
   {
		// Clear bit 0 and bit 4 in xEventGroup.
		xResult = xEventGroupClearBitsFromISR(
							xEventGroup,	 // The event group being updated.
							BIT_0 | BIT_4 ); // The bits being set.

		if( xResult == pdPASS )
		{
			// The message was posted successfully.
		}
  }
   </pre>
 * \defgroup xEventGroupClearBitsFromISR xEventGroupClearBitsFromISR
 * \ingroup EventGroup
 */
#if( configUSE_TRACE_FACILITY == 1 )
	BaseType_t xEventGroupClearBitsFromISR( EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToClear ) PRIVILEGED_FUNCTION;
#else
	#define xEventGroupClearBitsFromISR( xEventGroup, uxBitsToClear ) xTimerPendFunctionCallFromISR( vEventGroupClearBitsCallback, ( void * ) xEventGroup, ( uint32_t ) uxBitsToClear, NULL )
#endif

/**
 * event_groups.h
 *<pre>
	EventBits_t xEventGroupSetBits( EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToSet );
 </pre>
 *
 * Set bits within an event group.
 * This function cannot be called from an interrupt.  xEventGroupSetBitsFromISR()
 * is a version that can be called from an interrupt.
 *
 * Setting bits in an event group will automatically unblock tasks that are
 * blocked waiting for the bits.
 *
 * @param xEventGroup The event group in which the bits are to be set.
 *
 * @param uxBitsToSet A bitwise value that indicates the bit or bits to set.
 * For example, to set bit 3 only, set uxBitsToSet to 0x08.  To set bit 3
 * and bit 0 set uxBitsToSet to 0x09.
 *
 * @return The value of the event group at the time the call to
 * xEventGroupSetBits() returns.  There are two reasons why the returned value
 * might have the bits specified by the uxBitsToSet parameter cleared.  First,
 * if setting a bit results in a task that was waiting for the bit leaving the
 * blocked state then it is possible the bit will be cleared automatically
 * (see the xClearBitOnExit parameter of xEventGroupWaitBits()).  Second, any
 * unblocked (or otherwise Ready state) task that has a priority above that of
 * the task that called xEventGroupSetBits() will execute and may change the
 * event group value before the call to xEventGroupSetBits() returns.
 *
 * Example usage:
   <pre>
   #define BIT_0	( 1 << 0 )
   #define BIT_4	( 1 << 4 )

   void aFunction( EventGroupHandle_t xEventGroup )
   {
   EventBits_t uxBits;

		// Set bit 0 and bit 4 in xEventGroup.
		uxBits = xEventGroupSetBits(
							xEventGroup,	// The event group being updated.
							BIT_0 | BIT_4 );// The bits being set.

		if( ( uxBits & ( BIT_0 | BIT_4 ) ) == ( BIT_0 | BIT_4 ) )
		{
			// Both bit 0 and bit 4 remained set when the function returned.
		}
		else if( ( uxBits & BIT_0 ) != 0 )
		{
			// Bit 0 remained set when the function returned, but bit 4 was
			// cleared.  It might be that bit 4 was cleared automatically as a
			// task that was waiting for bit 4 was removed from the Blocked
			// state.
		}
		else if( ( uxBits & BIT_4 ) != 0 )
		{
			// Bit 4 remained set when the function returned, but bit 0 was
			// cleared.  It might be that bit 0 was cleared automatically as a
			// task that was waiting for bit 0 was removed from the Blocked
			// state.
		}
		else
		{
			// Neither bit 0 nor bit 4 remained set.  It might be that a task
			// was waiting for both of the bits to be set, and the bits were
			// cleared as the task left the Blocked state.
		}
   }
   </pre>
 * \defgroup xEventGroupSetBits xEventGroupSetBits
 * \ingroup EventGroup
 */
EventBits_t xEventGroupSetBits( EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToSet ) PRIVILEGED_FUNCTION;

/**
 * event_groups.h
 *<pre>
	BaseType_t xEventGroupSetBitsFromISR( EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToSet, BaseType_t *pxHigherPriorityTaskWoken );
 </pre>
 *
 * A version of xEventGroupSetBits() that can be called from an interrupt.
 *
 * Setting bits in an event group is not a deterministic operation because there
 * are an unknown number of tasks that may be waiting for the bit or bits being
 * set.  FreeRTOS does not allow nondeterministic operations to be performed in
 * interrupts or from critical sections.  Therefore xEventGroupSetBitsFromISR()
 * sends a message to the timer task to have the set operation performed in the
 * context of the timer task - where a scheduler lock is used in place of a
 * critical section.
 *
 * @param xEventGroup The event group in which the bits are to be set.
 *
 * @param uxBitsToSet A bitwise value that indicates the bit or bits to set.
 * For example, to set bit 3 only, set uxBitsToSet to 0x08.  To set bit 3
 * and bit 0 set uxBitsToSet to 0x09.
 *
 * @param pxHigherPriorityTaskWoken As mentioned above, calling this function
 * will result in a message being sent to the timer daemon task.  If the
 * priority of the timer daemon task is higher than the priority of the
 * currently running task (the task the interrupt interrupted) then
 * *pxHigherPriorityTaskWoken will be set to pdTRUE by
 * xEventGroupSetBitsFromISR(), indicating that a context switch should be
 * requested before the interrupt exits.  For that reason
 * *pxHigherPriorityTaskWoken must be initialised to pdFALSE.  See the
 * example code below.
 *
 * @return If the request to execute the function was posted successfully then
 * pdPASS is returned, otherwise pdFALSE is returned.  pdFALSE will be returned
 * if the timer service queue was full.
 *
 * Example usage:
   <pre>
   #define BIT_0	( 1 << 0 )
   #define BIT_4	( 1 << 4 )

   // An event group which it is assumed has already been created by a call to
   // xEventGroupCreate().
   EventGroupHandle_t xEventGroup;

   void anInterruptHandler( void )
   {
   BaseType_t xHigherPriorityTaskWoken, xResult;

		// xHigherPriorityTaskWoken must be initialised to pdFALSE.
		xHigherPriorityTaskWoken = pdFALSE;

		// Set bit 0 and bit 4 in xEventGroup.
		xResult = xEventGroupSetBitsFromISR(
							xEventGroup,	// The event group being updated.
							BIT_0 | BIT_4   // The bits being set.
							&xHigherPriorityTaskWoken );

		// Was the message posted successfully?
		if( xResult == pdPASS )
		{
			// If xHigherPriorityTaskWoken is now set to pdTRUE then a context
			// switch should be requested.  The macro used is port specific and
			// will be either portYIELD_FROM_ISR() or portEND_SWITCHING_ISR() -
			// refer to the documentation page for the port being used.
			portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
		}
  }
   </pre>
 * \defgroup xEventGroupSetBitsFromISR xEventGroupSetBitsFromISR
 * \ingroup EventGroup
 */
#if( configUSE_TRACE_FACILITY == 1 )
	BaseType_t xEventGroupSetBitsFromISR( EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToSet, BaseType_t *pxHigherPriorityTaskWoken ) PRIVILEGED_FUNCTION;
#else
	#define xEventGroupSetBitsFromISR( xEventGroup, uxBitsToSet, pxHigherPriorityTaskWoken ) xTimerPendFunctionCallFromISR( vEventGroupSetBitsCallback, ( void * ) xEventGroup, ( uint32_t ) uxBitsToSet, pxHigherPriorityTaskWoken )
#endif

/**
 * event_groups.h
 *<pre>
	EventBits_t xEventGroupSync(	EventGroupHandle_t xEventGroup,
									const EventBits_t uxBitsToSet,
									const EventBits_t uxBitsToWaitFor,
									TickType_t xTicksToWait );
 </pre>
 *
 * Atomically set bits within an event group, then wait for a combination of
 * bits to be set within the same event group.  This functionality is typically
 * used to synchronise multiple tasks, where each task has to wait for the other
 * tasks to reach a synchronisation point before proceeding.
 *
 * This function cannot be used from an interrupt.
 *
 * The function will return before its block time expires if the bits specified
 * by the uxBitsToWait parameter are set, or become set within that time.  In
 * this case all the bits specified by uxBitsToWait will be automatically
 * cleared before the function returns.
 *
 * @param xEventGroup The event group in which the bits are being tested.  The
 * event group must have previously been created using a call to
 * xEventGroupCreate().
 *
 * @param uxBitsToSet The bits to set in the event group before determining
 * if, and possibly waiting for, all the bits specified by the uxBitsToWait
 * parameter are set.
 *
 * @param uxBitsToWaitFor A bitwise value that indicates the bit or bits to test
 * inside the event group.  For example, to wait for bit 0 and bit 2 set
 * uxBitsToWaitFor to 0x05.  To wait for bits 0 and bit 1 and bit 2 set
 * uxBitsToWaitFor to 0x07.  Etc.
 *
 * @param xTicksToWait The maximum amount of time (specified in 'ticks') to wait
 * for all of the bits specified by uxBitsToWaitFor to become set.
 *
 * @return The value of the event group at the time either the bits being waited
 * for became set, or the block time expired.  Test the return value to know
 * which bits were set.  If xEventGroupSync() returned because its timeout
 * expired then not all the bits being waited for will be set.  If
 * xEventGroupSync() returned because all the bits it was waiting for were
 * set then the returned value is the event group value before any bits were
 * automatically cleared.
 *
 * Example usage:
 <pre>
 // Bits used by the three tasks.
 #define TASK_0_BIT		( 1 << 0 )
 #define TASK_1_BIT		( 1 << 1 )
 #define TASK_2_BIT		( 1 << 2 )

 #define ALL_SYNC_BITS ( TASK_0_BIT | TASK_1_BIT | TASK_2_BIT )

 // Use an event group to synchronise three tasks.  It is assumed this event
 // group has already been created elsewhere.
 EventGroupHandle_t xEventBits;

 void vTask0( void *pvParameters )
 {
 EventBits_t uxReturn;
 TickType_t xTicksToWait = 100 / portTICK_PERIOD_MS;

	 for( ;; )
	 {
		// Perform task functionality here.

		// Set bit 0 in the event flag to note this task has reached the
		// sync point.  The other two tasks will set the other two bits defined
		// by ALL_SYNC_BITS.  All three tasks have reached the synchronisation
		// point when all the ALL_SYNC_BITS are set.  Wait a maximum of 100ms
		// for this to happen.
		uxReturn = xEventGroupSync( xEventBits, TASK_0_BIT, ALL_SYNC_BITS, xTicksToWait );

		if( ( uxReturn & ALL_SYNC_BITS ) == ALL_SYNC_BITS )
		{
			// All three tasks reached the synchronisation point before the call
			// to xEventGroupSync() timed out.
		}
	}
 }

 void vTask1( void *pvParameters )
 {
	 for( ;; )
	 {
		// Perform task functionality here.

		// Set bit 1 in the event flag to note this task has reached the
		// synchronisation point.  The other two tasks will set the other two
		// bits defined by ALL_SYNC_BITS.  All three tasks have reached the
		// synchronisation point when all the ALL_SYNC_BITS are set.  Wait
		// indefinitely for this to happen.
		xEventGroupSync( xEventBits, TASK_1_BIT, ALL_SYNC_BITS, portMAX_DELAY );

		// xEventGroupSync() was called with an indefinite block time, so
		// this task will only reach here if the syncrhonisation was made by all
		// three tasks, so there is no need to test the return value.
	 }
 }

 void vTask2( void *pvParameters )
 {
	 for( ;; )
	 {
		// Perform task functionality here.

		// Set bit 2 in the event flag to note this task has reached the
		// synchronisation point.  The other two tasks will set the other two
		// bits defined by ALL_SYNC_BITS.  All three tasks have reached the
		// synchronisation point when all the ALL_SYNC_BITS are set.  Wait
		// indefinitely for this to happen.
		xEventGroupSync( xEventBits, TASK_2_BIT, ALL_SYNC_BITS, portMAX_DELAY );

		// xEventGroupSync() was called with an indefinite block time, so
		// this task will only reach here if the syncrhonisation was made by all
		// three tasks, so there is no need to test the return value.
	}
 }

 </pre>
 * \defgroup xEventGroupSync xEventGroupSync
 * \ingroup EventGroup
 */
EventBits_t xEventGroupSync( EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToSet, const EventBits_t uxBitsToWaitFor, TickType_t xTicksToWait ) PRIVILEGED_FUNCTION;


/**
 * event_groups.h
 *<pre>
	EventBits_t xEventGroupGetBits( EventGroupHandle_t xEventGroup );
 </pre>
 *
 * Returns the current value of the bits in an event group.  This function
 * cannot be used from an interrupt.
 *
 * @param xEventGroup The event group being queried.
 *
 * @return The event group bits at the time xEventGroupGetBits() was called.
 *
 * \defgroup xEventGroupGetBits xEventGroupGetBits
 * \ingroup EventGroup
 */
#define xEventGroupGetBits( xEventGroup ) xEventGroupClearBits( xEventGroup, 0 )

/**
 * event_groups.h
 *<pre>
	EventBits_t xEventGroupGetBitsFromISR( EventGroupHandle_t xEventGroup );
 </pre>
 *
 * A version of xEventGroupGetBits() that can be called from an ISR.
 *
 * @param xEventGroup The event group being queried.
 *
 * @return The event group bits at the time xEventGroupGetBitsFromISR() was called.
 *
 * \defgroup xEventGroupGetBitsFromISR xEventGroupGetBitsFromISR
 * \ingroup EventGroup
 */
EventBits_t xEventGroupGetBitsFromISR( EventGroupHandle_t xEventGroup ) PRIVILEGED_FUNCTION;

/**
 * event_groups.h
 *<pre>
	void xEventGroupDelete( EventGroupHandle_t xEventGroup );
 </pre>
 *
 * Delete an event group that was previously created by a call to
 * xEventGroupCreate().  Tasks that are blocked on the event group will be
 * unblocked and obtain 0 as the event group's value.
 *
 * @param xEventGroup The event group being deleted.
 */
void vEventGroupDelete( EventGroupHandle_t xEventGroup ) PRIVILEGED_FUNCTION;

/* For internal use only. */
void vEventGroupSetBitsCallback( void *pvEventGroup, const uint32_t ulBitsToSet ) PRIVILEGED_FUNCTION;
void vEventGroupClearBitsCallback( void *pvEventGroup, const uint32_t ulBitsToClear ) PRIVILEGED_FUNCTION;


#if (configUSE_TRACE_FACILITY == 1)
	UBaseType_t uxEventGroupGetNumber( void* xEventGroup ) PRIVILEGED_FUNCTION;
	void vEventGroupSetNumber( void* xEventGroup, UBaseType_t uxEventGroupNumber ) PRIVILEGED_FUNCTION;
#endif

#ifdef __cplusplus
}
#endif

#endif /* EVENT_GROUPS_H */