timers.c

Go to the documentation of this file.

/*
    FreeRTOS V8.2.3 - Copyright (C) 2015 Real Time Engineers Ltd.
    All rights reserved

    VISIT http://www.FreeRTOS.org TO ENSURE YOU ARE USING THE LATEST VERSION.

    This file is part of the FreeRTOS distribution.

    FreeRTOS is free software; you can redistribute it and/or modify it under
    the terms of the GNU General Public License (version 2) as published by the
    Free Software Foundation >>>> AND MODIFIED BY <<<< the FreeRTOS exception.

    ***************************************************************************
    >>!   NOTE: The modification to the GPL is included to allow you to     !<<
    >>!   distribute a combined work that includes FreeRTOS without being   !<<
    >>!   obliged to provide the source code for proprietary components     !<<
    >>!   outside of the FreeRTOS kernel.                                   !<<
    ***************************************************************************

    FreeRTOS is distributed in the hope that it will be useful, but WITHOUT ANY
    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
    FOR A PARTICULAR PURPOSE.  Full license text is available on the following
    link: http://www.freertos.org/a00114.html

    ***************************************************************************
     *                                                                       *
     *    FreeRTOS provides completely free yet professionally developed,    *
     *    robust, strictly quality controlled, supported, and cross          *
     *    platform software that is more than just the market leader, it     *
     *    is the industry's de facto standard.                               *
     *                                                                       *
     *    Help yourself get started quickly while simultaneously helping     *
     *    to support the FreeRTOS project by purchasing a FreeRTOS           *
     *    tutorial book, reference manual, or both:                          *
     *    http://www.FreeRTOS.org/Documentation                              *
     *                                                                       *
    ***************************************************************************

    http://www.FreeRTOS.org/FAQHelp.html - Having a problem?  Start by reading
    the FAQ page "My application does not run, what could be wrong?".  Have you
    defined configASSERT()?

    http://www.FreeRTOS.org/support - In return for receiving this top quality
    embedded software for free we request you assist our global community by
    participating in the support forum.

    http://www.FreeRTOS.org/training - Investing in training allows your team to
    be as productive as possible as early as possible.  Now you can receive
    FreeRTOS training directly from Richard Barry, CEO of Real Time Engineers
    Ltd, and the world's leading authority on the world's leading RTOS.

    http://www.FreeRTOS.org/plus - A selection of FreeRTOS ecosystem products,
    including FreeRTOS+Trace - an indispensable productivity tool, a DOS
    compatible FAT file system, and our tiny thread aware UDP/IP stack.

    http://www.FreeRTOS.org/labs - Where new FreeRTOS products go to incubate.
    Come and try FreeRTOS+TCP, our new open source TCP/IP stack for FreeRTOS.

    http://www.OpenRTOS.com - Real Time Engineers ltd. license FreeRTOS to High
    Integrity Systems ltd. to sell under the OpenRTOS brand.  Low cost OpenRTOS
    licenses offer ticketed support, indemnification and commercial middleware.

    http://www.SafeRTOS.com - High Integrity Systems also provide a safety
    engineered and independently SIL3 certified version for use in safety and
    mission critical applications that require provable dependability.

    1 tab == 4 spaces!
*/

/* Standard includes. */
#include <stdlib.h>

/* Defining MPU_WRAPPERS_INCLUDED_FROM_API_FILE prevents task.h from redefining
all the API functions to use the MPU wrappers.  That should only be done when
task.h is included from an application file. */
#define MPU_WRAPPERS_INCLUDED_FROM_API_FILE

#include "FreeRTOS.h"
#include "task.h"
#include "queue.h"
#include "timers.h"

#if ( INCLUDE_xTimerPendFunctionCall == 1 ) && ( configUSE_TIMERS == 0 )
    #error configUSE_TIMERS must be set to 1 to make the xTimerPendFunctionCall() function available.
#endif

/* Lint e961 and e750 are suppressed as a MISRA exception justified because the
MPU ports require MPU_WRAPPERS_INCLUDED_FROM_API_FILE to be defined for the
header files above, but not in this file, in order to generate the correct
privileged Vs unprivileged linkage and placement. */
#undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE /*lint !e961 !e750. */


/* This entire source file will be skipped if the application is not configured
to include software timer functionality.  This #if is closed at the very bottom
of this file.  If you want to include software timer functionality then ensure
configUSE_TIMERS is set to 1 in FreeRTOSConfig.h. */
#if ( configUSE_TIMERS == 1 )

/* Misc definitions. */
#define tmrNO_DELAY     ( TickType_t ) 0U

/* The definition of the timers themselves. */
typedef struct tmrTimerControl
{
    const char              *pcTimerName;       /*<< Text name.  This is not used by the kernel, it is included simply to make debugging easier. */ /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
    ListItem_t              xTimerListItem;     /*<< Standard linked list item as used by all kernel features for event management. */
    TickType_t              xTimerPeriodInTicks;/*<< How quickly and often the timer expires. */
    UBaseType_t             uxAutoReload;       /*<< Set to pdTRUE if the timer should be automatically restarted once expired.  Set to pdFALSE if the timer is, in effect, a one-shot timer. */
    void                    *pvTimerID;         /*<< An ID to identify the timer.  This allows the timer to be identified when the same callback is used for multiple timers. */
    TimerCallbackFunction_t pxCallbackFunction; /*<< The function that will be called when the timer expires. */
    #if( configUSE_TRACE_FACILITY == 1 )
        UBaseType_t         uxTimerNumber;      /*<< An ID assigned by trace tools such as FreeRTOS+Trace */
    #endif
} xTIMER;

/* The old xTIMER name is maintained above then typedefed to the new Timer_t
name below to enable the use of older kernel aware debuggers. */
typedef xTIMER Timer_t;

/* The definition of messages that can be sent and received on the timer queue.
Two types of message can be queued - messages that manipulate a software timer,
and messages that request the execution of a non-timer related callback.  The
two message types are defined in two separate structures, xTimerParametersType
and xCallbackParametersType respectively. */
typedef struct tmrTimerParameters
{
    TickType_t          xMessageValue;      /*<< An optional value used by a subset of commands, for example, when changing the period of a timer. */
    Timer_t *           pxTimer;            /*<< The timer to which the command will be applied. */
} TimerParameter_t;


typedef struct tmrCallbackParameters
{
    PendedFunction_t    pxCallbackFunction; /* << The callback function to execute. */
    void *pvParameter1;                     /* << The value that will be used as the callback functions first parameter. */
    uint32_t ulParameter2;                  /* << The value that will be used as the callback functions second parameter. */
} CallbackParameters_t;

/* The structure that contains the two message types, along with an identifier
that is used to determine which message type is valid. */
typedef struct tmrTimerQueueMessage
{
    BaseType_t          xMessageID;         /*<< The command being sent to the timer service task. */
    union
    {
        TimerParameter_t xTimerParameters;

        /* Don't include xCallbackParameters if it is not going to be used as
        it makes the structure (and therefore the timer queue) larger. */
        #if ( INCLUDE_xTimerPendFunctionCall == 1 )
            CallbackParameters_t xCallbackParameters;
        #endif /* INCLUDE_xTimerPendFunctionCall */
    } u;
} DaemonTaskMessage_t;

/*lint -e956 A manual analysis and inspection has been used to determine which
static variables must be declared volatile. */

/* The list in which active timers are stored.  Timers are referenced in expire
time order, with the nearest expiry time at the front of the list.  Only the
timer service task is allowed to access these lists. */
PRIVILEGED_DATA static List_t xActiveTimerList1;
PRIVILEGED_DATA static List_t xActiveTimerList2;
PRIVILEGED_DATA static List_t *pxCurrentTimerList;
PRIVILEGED_DATA static List_t *pxOverflowTimerList;

/* A queue that is used to send commands to the timer service task. */
PRIVILEGED_DATA static QueueHandle_t xTimerQueue = NULL;

#if ( INCLUDE_xTimerGetTimerDaemonTaskHandle == 1 )

    PRIVILEGED_DATA static TaskHandle_t xTimerTaskHandle = NULL;

#endif

/*lint +e956 */

/*-----------------------------------------------------------*/

/*
 * Initialise the infrastructure used by the timer service task if it has not
 * been initialised already.
 */
static void prvCheckForValidListAndQueue( void ) PRIVILEGED_FUNCTION;

/*
 * The timer service task (daemon).  Timer functionality is controlled by this
 * task.  Other tasks communicate with the timer service task using the
 * xTimerQueue queue.
 */
static void prvTimerTask( void *pvParameters ) PRIVILEGED_FUNCTION;

/*
 * Called by the timer service task to interpret and process a command it
 * received on the timer queue.
 */
static void prvProcessReceivedCommands( void ) PRIVILEGED_FUNCTION;

/*
 * Insert the timer into either xActiveTimerList1, or xActiveTimerList2,
 * depending on if the expire time causes a timer counter overflow.
 */
static BaseType_t prvInsertTimerInActiveList( Timer_t * const pxTimer, const TickType_t xNextExpiryTime, const TickType_t xTimeNow, const TickType_t xCommandTime ) PRIVILEGED_FUNCTION;

/*
 * An active timer has reached its expire time.  Reload the timer if it is an
 * auto reload timer, then call its callback.
 */
static void prvProcessExpiredTimer( const TickType_t xNextExpireTime, const TickType_t xTimeNow ) PRIVILEGED_FUNCTION;

/*
 * The tick count has overflowed.  Switch the timer lists after ensuring the
 * current timer list does not still reference some timers.
 */
static void prvSwitchTimerLists( void ) PRIVILEGED_FUNCTION;

/*
 * Obtain the current tick count, setting *pxTimerListsWereSwitched to pdTRUE
 * if a tick count overflow occurred since prvSampleTimeNow() was last called.
 */
static TickType_t prvSampleTimeNow( BaseType_t * const pxTimerListsWereSwitched ) PRIVILEGED_FUNCTION;

/*
 * If the timer list contains any active timers then return the expire time of
 * the timer that will expire first and set *pxListWasEmpty to false.  If the
 * timer list does not contain any timers then return 0 and set *pxListWasEmpty
 * to pdTRUE.
 */
static TickType_t prvGetNextExpireTime( BaseType_t * const pxListWasEmpty ) PRIVILEGED_FUNCTION;

/*
 * If a timer has expired, process it.  Otherwise, block the timer service task
 * until either a timer does expire or a command is received.
 */
static void prvProcessTimerOrBlockTask( const TickType_t xNextExpireTime, BaseType_t xListWasEmpty ) PRIVILEGED_FUNCTION;

/*-----------------------------------------------------------*/

BaseType_t xTimerCreateTimerTask( void )
{
BaseType_t xReturn = pdFAIL;

    /* This function is called when the scheduler is started if
    configUSE_TIMERS is set to 1.  Check that the infrastructure used by the
    timer service task has been created/initialised.  If timers have already
    been created then the initialisation will already have been performed. */
    prvCheckForValidListAndQueue();

    if( xTimerQueue != NULL )
    {
        #if ( INCLUDE_xTimerGetTimerDaemonTaskHandle == 1 )
        {
            /* Create the timer task, storing its handle in xTimerTaskHandle so
            it can be returned by the xTimerGetTimerDaemonTaskHandle() function. */
            xReturn = xTaskCreate( prvTimerTask, "Tmr Svc", ( uint16_t ) configTIMER_TASK_STACK_DEPTH, NULL, ( ( UBaseType_t ) configTIMER_TASK_PRIORITY ) | portPRIVILEGE_BIT, &xTimerTaskHandle );
        }
        #else
        {
            /* Create the timer task without storing its handle. */
            xReturn = xTaskCreate( prvTimerTask, "Tmr Svc", ( uint16_t ) configTIMER_TASK_STACK_DEPTH, NULL, ( ( UBaseType_t ) configTIMER_TASK_PRIORITY ) | portPRIVILEGE_BIT, NULL);
        }
        #endif
    }
    else
    {
        mtCOVERAGE_TEST_MARKER();
    }

    configASSERT( xReturn );
    return xReturn;
}
/*-----------------------------------------------------------*/

TimerHandle_t xTimerCreate( const char * const pcTimerName, const TickType_t xTimerPeriodInTicks, const UBaseType_t uxAutoReload, void * const pvTimerID, TimerCallbackFunction_t pxCallbackFunction ) /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
{
Timer_t *pxNewTimer;

    /* Allocate the timer structure. */
    if( xTimerPeriodInTicks == ( TickType_t ) 0U )
    {
        pxNewTimer = NULL;
    }
    else
    {
        pxNewTimer = ( Timer_t * ) pvPortMalloc( sizeof( Timer_t ) );
        if( pxNewTimer != NULL )
        {
            /* Ensure the infrastructure used by the timer service task has been
            created/initialised. */
            prvCheckForValidListAndQueue();

            /* Initialise the timer structure members using the function parameters. */
            pxNewTimer->pcTimerName = pcTimerName;
            pxNewTimer->xTimerPeriodInTicks = xTimerPeriodInTicks;
            pxNewTimer->uxAutoReload = uxAutoReload;
            pxNewTimer->pvTimerID = pvTimerID;
            pxNewTimer->pxCallbackFunction = pxCallbackFunction;
            vListInitialiseItem( &( pxNewTimer->xTimerListItem ) );

            traceTIMER_CREATE( pxNewTimer );
        }
        else
        {
            traceTIMER_CREATE_FAILED();
        }
    }

    /* 0 is not a valid value for xTimerPeriodInTicks. */
    configASSERT( ( xTimerPeriodInTicks > 0 ) );

    return ( TimerHandle_t ) pxNewTimer;
}
/*-----------------------------------------------------------*/

BaseType_t xTimerGenericCommand( TimerHandle_t xTimer, const BaseType_t xCommandID, const TickType_t xOptionalValue, BaseType_t * const pxHigherPriorityTaskWoken, const TickType_t xTicksToWait )
{
BaseType_t xReturn = pdFAIL;
DaemonTaskMessage_t xMessage;

    configASSERT( xTimer );

    /* Send a message to the timer service task to perform a particular action
    on a particular timer definition. */
    if( xTimerQueue != NULL )
    {
        /* Send a command to the timer service task to start the xTimer timer. */
        xMessage.xMessageID = xCommandID;
        xMessage.u.xTimerParameters.xMessageValue = xOptionalValue;
        xMessage.u.xTimerParameters.pxTimer = ( Timer_t * ) xTimer;

        if( xCommandID < tmrFIRST_FROM_ISR_COMMAND )
        {
            if( xTaskGetSchedulerState() == taskSCHEDULER_RUNNING )
            {
                xReturn = xQueueSendToBack( xTimerQueue, &xMessage, xTicksToWait );
            }
            else
            {
                xReturn = xQueueSendToBack( xTimerQueue, &xMessage, tmrNO_DELAY );
            }
        }
        else
        {
            xReturn = xQueueSendToBackFromISR( xTimerQueue, &xMessage, pxHigherPriorityTaskWoken );
        }

        traceTIMER_COMMAND_SEND( xTimer, xCommandID, xOptionalValue, xReturn );
    }
    else
    {
        mtCOVERAGE_TEST_MARKER();
    }

    return xReturn;
}
/*-----------------------------------------------------------*/

#if ( INCLUDE_xTimerGetTimerDaemonTaskHandle == 1 )

    TaskHandle_t xTimerGetTimerDaemonTaskHandle( void )
    {
        /* If xTimerGetTimerDaemonTaskHandle() is called before the scheduler has been
        started, then xTimerTaskHandle will be NULL. */
        configASSERT( ( xTimerTaskHandle != NULL ) );
        return xTimerTaskHandle;
    }

#endif
/*-----------------------------------------------------------*/

const char * pcTimerGetTimerName( TimerHandle_t xTimer )
{
Timer_t *pxTimer = ( Timer_t * ) xTimer;

    configASSERT( xTimer );
    return pxTimer->pcTimerName;
}
/*-----------------------------------------------------------*/

static void prvProcessExpiredTimer( const TickType_t xNextExpireTime, const TickType_t xTimeNow )
{
BaseType_t xResult;
Timer_t * const pxTimer = ( Timer_t * ) listGET_OWNER_OF_HEAD_ENTRY( pxCurrentTimerList );

    /* Remove the timer from the list of active timers.  A check has already
    been performed to ensure the list is not empty. */
    ( void ) uxListRemove( &( pxTimer->xTimerListItem ) );
    traceTIMER_EXPIRED( pxTimer );

    /* If the timer is an auto reload timer then calculate the next
    expiry time and re-insert the timer in the list of active timers. */
    if( pxTimer->uxAutoReload == ( UBaseType_t ) pdTRUE )
    {
        /* The timer is inserted into a list using a time relative to anything
        other than the current time.  It will therefore be inserted into the
        correct list relative to the time this task thinks it is now. */
        if( prvInsertTimerInActiveList( pxTimer, ( xNextExpireTime + pxTimer->xTimerPeriodInTicks ), xTimeNow, xNextExpireTime ) == pdTRUE )
        {
            /* The timer expired before it was added to the active timer
            list.  Reload it now.  */
            xResult = xTimerGenericCommand( pxTimer, tmrCOMMAND_START_DONT_TRACE, xNextExpireTime, NULL, tmrNO_DELAY );
            configASSERT( xResult );
            ( void ) xResult;
        }
        else
        {
            mtCOVERAGE_TEST_MARKER();
        }
    }
    else
    {
        mtCOVERAGE_TEST_MARKER();
    }

    /* Call the timer callback. */
    pxTimer->pxCallbackFunction( ( TimerHandle_t ) pxTimer );
}
/*-----------------------------------------------------------*/

static void prvTimerTask( void *pvParameters )
{
TickType_t xNextExpireTime;
BaseType_t xListWasEmpty;

    /* Just to avoid compiler warnings. */
    ( void ) pvParameters;

    for( ;; )
    {
        /* Query the timers list to see if it contains any timers, and if so,
        obtain the time at which the next timer will expire. */
        xNextExpireTime = prvGetNextExpireTime( &xListWasEmpty );

        /* If a timer has expired, process it.  Otherwise, block this task
        until either a timer does expire, or a command is received. */
        prvProcessTimerOrBlockTask( xNextExpireTime, xListWasEmpty );

        /* Empty the command queue. */
        prvProcessReceivedCommands();
    }
}
/*-----------------------------------------------------------*/

static void prvProcessTimerOrBlockTask( const TickType_t xNextExpireTime, BaseType_t xListWasEmpty )
{
TickType_t xTimeNow;
BaseType_t xTimerListsWereSwitched;

    vTaskSuspendAll();
    {
        /* Obtain the time now to make an assessment as to whether the timer
        has expired or not.  If obtaining the time causes the lists to switch
        then don't process this timer as any timers that remained in the list
        when the lists were switched will have been processed within the
        prvSampleTimeNow() function. */
        xTimeNow = prvSampleTimeNow( &xTimerListsWereSwitched );
        if( xTimerListsWereSwitched == pdFALSE )
        {
            /* The tick count has not overflowed, has the timer expired? */
            if( ( xListWasEmpty == pdFALSE ) && ( xNextExpireTime <= xTimeNow ) )
            {
                ( void ) xTaskResumeAll();
                prvProcessExpiredTimer( xNextExpireTime, xTimeNow );
            }
            else
            {
                /* The tick count has not overflowed, and the next expire
                time has not been reached yet.  This task should therefore
                block to wait for the next expire time or a command to be
                received - whichever comes first.  The following line cannot
                be reached unless xNextExpireTime > xTimeNow, except in the
                case when the current timer list is empty. */
                if( xListWasEmpty != pdFALSE )
                {
                    /* The current timer list is empty - is the overflow list
                    also empty? */
                    xListWasEmpty = listLIST_IS_EMPTY( pxOverflowTimerList );
                }

                vQueueWaitForMessageRestricted( xTimerQueue, ( xNextExpireTime - xTimeNow ), xListWasEmpty );

                if( xTaskResumeAll() == pdFALSE )
                {
                    /* Yield to wait for either a command to arrive, or the
                    block time to expire.  If a command arrived between the
                    critical section being exited and this yield then the yield
                    will not cause the task to block. */
                    portYIELD_WITHIN_API();
                }
                else
                {
                    mtCOVERAGE_TEST_MARKER();
                }
            }
        }
        else
        {
            ( void ) xTaskResumeAll();
        }
    }
}
/*-----------------------------------------------------------*/

static TickType_t prvGetNextExpireTime( BaseType_t * const pxListWasEmpty )
{
TickType_t xNextExpireTime;

    /* Timers are listed in expiry time order, with the head of the list
    referencing the task that will expire first.  Obtain the time at which
    the timer with the nearest expiry time will expire.  If there are no
    active timers then just set the next expire time to 0.  That will cause
    this task to unblock when the tick count overflows, at which point the
    timer lists will be switched and the next expiry time can be
    re-assessed.  */
    *pxListWasEmpty = listLIST_IS_EMPTY( pxCurrentTimerList );
    if( *pxListWasEmpty == pdFALSE )
    {
        xNextExpireTime = listGET_ITEM_VALUE_OF_HEAD_ENTRY( pxCurrentTimerList );
    }
    else
    {
        /* Ensure the task unblocks when the tick count rolls over. */
        xNextExpireTime = ( TickType_t ) 0U;
    }

    return xNextExpireTime;
}
/*-----------------------------------------------------------*/

static TickType_t prvSampleTimeNow( BaseType_t * const pxTimerListsWereSwitched )
{
TickType_t xTimeNow;
PRIVILEGED_DATA static TickType_t xLastTime = ( TickType_t ) 0U; /*lint !e956 Variable is only accessible to one task. */

    xTimeNow = xTaskGetTickCount();

    if( xTimeNow < xLastTime )
    {
        prvSwitchTimerLists();
        *pxTimerListsWereSwitched = pdTRUE;
    }
    else
    {
        *pxTimerListsWereSwitched = pdFALSE;
    }

    xLastTime = xTimeNow;

    return xTimeNow;
}
/*-----------------------------------------------------------*/

static BaseType_t prvInsertTimerInActiveList( Timer_t * const pxTimer, const TickType_t xNextExpiryTime, const TickType_t xTimeNow, const TickType_t xCommandTime )
{
BaseType_t xProcessTimerNow = pdFALSE;

    listSET_LIST_ITEM_VALUE( &( pxTimer->xTimerListItem ), xNextExpiryTime );
    listSET_LIST_ITEM_OWNER( &( pxTimer->xTimerListItem ), pxTimer );

    if( xNextExpiryTime <= xTimeNow )
    {
        /* Has the expiry time elapsed between the command to start/reset a
        timer was issued, and the time the command was processed? */
        if( ( xTimeNow - xCommandTime ) >= pxTimer->xTimerPeriodInTicks )
        {
            /* The time between a command being issued and the command being
            processed actually exceeds the timers period.  */
            xProcessTimerNow = pdTRUE;
        }
        else
        {
            vListInsert( pxOverflowTimerList, &( pxTimer->xTimerListItem ) );
        }
    }
    else
    {
        if( ( xTimeNow < xCommandTime ) && ( xNextExpiryTime >= xCommandTime ) )
        {
            /* If, since the command was issued, the tick count has overflowed
            but the expiry time has not, then the timer must have already passed
            its expiry time and should be processed immediately. */
            xProcessTimerNow = pdTRUE;
        }
        else
        {
            vListInsert( pxCurrentTimerList, &( pxTimer->xTimerListItem ) );
        }
    }

    return xProcessTimerNow;
}
/*-----------------------------------------------------------*/

static void prvProcessReceivedCommands( void )
{
DaemonTaskMessage_t xMessage;
Timer_t *pxTimer;
BaseType_t xTimerListsWereSwitched, xResult;
TickType_t xTimeNow;

    while( xQueueReceive( xTimerQueue, &xMessage, tmrNO_DELAY ) != pdFAIL ) /*lint !e603 xMessage does not have to be initialised as it is passed out, not in, and it is not used unless xQueueReceive() returns pdTRUE. */
    {
        #if ( INCLUDE_xTimerPendFunctionCall == 1 )
        {
            /* Negative commands are pended function calls rather than timer
            commands. */
            if( xMessage.xMessageID < ( BaseType_t ) 0 )
            {
                const CallbackParameters_t * const pxCallback = &( xMessage.u.xCallbackParameters );

                /* The timer uses the xCallbackParameters member to request a
                callback be executed.  Check the callback is not NULL. */
                configASSERT( pxCallback );

                /* Call the function. */
                pxCallback->pxCallbackFunction( pxCallback->pvParameter1, pxCallback->ulParameter2 );
            }
            else
            {
                mtCOVERAGE_TEST_MARKER();
            }
        }
        #endif /* INCLUDE_xTimerPendFunctionCall */

        /* Commands that are positive are timer commands rather than pended
        function calls. */
        if( xMessage.xMessageID >= ( BaseType_t ) 0 )
        {
            /* The messages uses the xTimerParameters member to work on a
            software timer. */
            pxTimer = xMessage.u.xTimerParameters.pxTimer;

            if( listIS_CONTAINED_WITHIN( NULL, &( pxTimer->xTimerListItem ) ) == pdFALSE )
            {
                /* The timer is in a list, remove it. */
                ( void ) uxListRemove( &( pxTimer->xTimerListItem ) );
            }
            else
            {
                mtCOVERAGE_TEST_MARKER();
            }

            traceTIMER_COMMAND_RECEIVED( pxTimer, xMessage.xMessageID, xMessage.u.xTimerParameters.xMessageValue );

            /* In this case the xTimerListsWereSwitched parameter is not used, but
            it must be present in the function call.  prvSampleTimeNow() must be
            called after the message is received from xTimerQueue so there is no
            possibility of a higher priority task adding a message to the message
            queue with a time that is ahead of the timer daemon task (because it
            pre-empted the timer daemon task after the xTimeNow value was set). */
            xTimeNow = prvSampleTimeNow( &xTimerListsWereSwitched );

            switch( xMessage.xMessageID )
            {
                case tmrCOMMAND_START :
                case tmrCOMMAND_START_FROM_ISR :
                case tmrCOMMAND_RESET :
                case tmrCOMMAND_RESET_FROM_ISR :
                case tmrCOMMAND_START_DONT_TRACE :
                    /* Start or restart a timer. */
                    if( prvInsertTimerInActiveList( pxTimer,  xMessage.u.xTimerParameters.xMessageValue + pxTimer->xTimerPeriodInTicks, xTimeNow, xMessage.u.xTimerParameters.xMessageValue ) == pdTRUE )
                    {
                        /* The timer expired before it was added to the active
                        timer list.  Process it now. */
                        pxTimer->pxCallbackFunction( ( TimerHandle_t ) pxTimer );
                        traceTIMER_EXPIRED( pxTimer );

                        if( pxTimer->uxAutoReload == ( UBaseType_t ) pdTRUE )
                        {
                            xResult = xTimerGenericCommand( pxTimer, tmrCOMMAND_START_DONT_TRACE, xMessage.u.xTimerParameters.xMessageValue + pxTimer->xTimerPeriodInTicks, NULL, tmrNO_DELAY );
                            configASSERT( xResult );
                            ( void ) xResult;
                        }
                        else
                        {
                            mtCOVERAGE_TEST_MARKER();
                        }
                    }
                    else
                    {
                        mtCOVERAGE_TEST_MARKER();
                    }
                    break;

                case tmrCOMMAND_STOP :
                case tmrCOMMAND_STOP_FROM_ISR :
                    /* The timer has already been removed from the active list.
                    There is nothing to do here. */
                    break;

                case tmrCOMMAND_CHANGE_PERIOD :
                case tmrCOMMAND_CHANGE_PERIOD_FROM_ISR :
                    pxTimer->xTimerPeriodInTicks = xMessage.u.xTimerParameters.xMessageValue;
                    configASSERT( ( pxTimer->xTimerPeriodInTicks > 0 ) );

                    /* The new period does not really have a reference, and can be
                    longer or shorter than the old one.  The command time is
                    therefore set to the current time, and as the period cannot be
                    zero the next expiry time can only be in the future, meaning
                    (unlike for the xTimerStart() case above) there is no fail case
                    that needs to be handled here. */
                    ( void ) prvInsertTimerInActiveList( pxTimer, ( xTimeNow + pxTimer->xTimerPeriodInTicks ), xTimeNow, xTimeNow );
                    break;

                case tmrCOMMAND_DELETE :
                    /* The timer has already been removed from the active list,
                    just free up the memory. */
                    vPortFree( pxTimer );
                    break;

                default :
                    /* Don't expect to get here. */
                    break;
            }
        }
    }
}
/*-----------------------------------------------------------*/

static void prvSwitchTimerLists( void )
{
TickType_t xNextExpireTime, xReloadTime;
List_t *pxTemp;
Timer_t *pxTimer;
BaseType_t xResult;

    /* The tick count has overflowed.  The timer lists must be switched.
    If there are any timers still referenced from the current timer list
    then they must have expired and should be processed before the lists
    are switched. */
    while( listLIST_IS_EMPTY( pxCurrentTimerList ) == pdFALSE )
    {
        xNextExpireTime = listGET_ITEM_VALUE_OF_HEAD_ENTRY( pxCurrentTimerList );

        /* Remove the timer from the list. */
        pxTimer = ( Timer_t * ) listGET_OWNER_OF_HEAD_ENTRY( pxCurrentTimerList );
        ( void ) uxListRemove( &( pxTimer->xTimerListItem ) );
        traceTIMER_EXPIRED( pxTimer );

        /* Execute its callback, then send a command to restart the timer if
        it is an auto-reload timer.  It cannot be restarted here as the lists
        have not yet been switched. */
        pxTimer->pxCallbackFunction( ( TimerHandle_t ) pxTimer );

        if( pxTimer->uxAutoReload == ( UBaseType_t ) pdTRUE )
        {
            /* Calculate the reload value, and if the reload value results in
            the timer going into the same timer list then it has already expired
            and the timer should be re-inserted into the current list so it is
            processed again within this loop.  Otherwise a command should be sent
            to restart the timer to ensure it is only inserted into a list after
            the lists have been swapped. */
            xReloadTime = ( xNextExpireTime + pxTimer->xTimerPeriodInTicks );
            if( xReloadTime > xNextExpireTime )
            {
                listSET_LIST_ITEM_VALUE( &( pxTimer->xTimerListItem ), xReloadTime );
                listSET_LIST_ITEM_OWNER( &( pxTimer->xTimerListItem ), pxTimer );
                vListInsert( pxCurrentTimerList, &( pxTimer->xTimerListItem ) );
            }
            else
            {
                xResult = xTimerGenericCommand( pxTimer, tmrCOMMAND_START_DONT_TRACE, xNextExpireTime, NULL, tmrNO_DELAY );
                configASSERT( xResult );
                ( void ) xResult;
            }
        }
        else
        {
            mtCOVERAGE_TEST_MARKER();
        }
    }

    pxTemp = pxCurrentTimerList;
    pxCurrentTimerList = pxOverflowTimerList;
    pxOverflowTimerList = pxTemp;
}
/*-----------------------------------------------------------*/

static void prvCheckForValidListAndQueue( void )
{
    /* Check that the list from which active timers are referenced, and the
    queue used to communicate with the timer service, have been
    initialised. */
    taskENTER_CRITICAL();
    {
        if( xTimerQueue == NULL )
        {
            vListInitialise( &xActiveTimerList1 );
            vListInitialise( &xActiveTimerList2 );
            pxCurrentTimerList = &xActiveTimerList1;
            pxOverflowTimerList = &xActiveTimerList2;
            xTimerQueue = xQueueCreate( ( UBaseType_t ) configTIMER_QUEUE_LENGTH, sizeof( DaemonTaskMessage_t ) );
            configASSERT( xTimerQueue );

            #if ( configQUEUE_REGISTRY_SIZE > 0 )
            {
                if( xTimerQueue != NULL )
                {
                    vQueueAddToRegistry( xTimerQueue, "TmrQ" );
                }
                else
                {
                    mtCOVERAGE_TEST_MARKER();
                }
            }
            #endif /* configQUEUE_REGISTRY_SIZE */
        }
        else
        {
            mtCOVERAGE_TEST_MARKER();
        }
    }
    taskEXIT_CRITICAL();
}
/*-----------------------------------------------------------*/

BaseType_t xTimerIsTimerActive( TimerHandle_t xTimer )
{
BaseType_t xTimerIsInActiveList;
Timer_t *pxTimer = ( Timer_t * ) xTimer;

    configASSERT( xTimer );

    /* Is the timer in the list of active timers? */
    taskENTER_CRITICAL();
    {
        /* Checking to see if it is in the NULL list in effect checks to see if
        it is referenced from either the current or the overflow timer lists in
        one go, but the logic has to be reversed, hence the '!'. */
        xTimerIsInActiveList = ( BaseType_t ) !( listIS_CONTAINED_WITHIN( NULL, &( pxTimer->xTimerListItem ) ) );
    }
    taskEXIT_CRITICAL();

    return xTimerIsInActiveList;
} /*lint !e818 Can't be pointer to const due to the typedef. */
/*-----------------------------------------------------------*/

void *pvTimerGetTimerID( const TimerHandle_t xTimer )
{
Timer_t * const pxTimer = ( Timer_t * ) xTimer;
void *pvReturn;

    configASSERT( xTimer );

    taskENTER_CRITICAL();
    {
        pvReturn = pxTimer->pvTimerID;
    }
    taskEXIT_CRITICAL();

    return pvReturn;
}
/*-----------------------------------------------------------*/

void vTimerSetTimerID( TimerHandle_t xTimer, void *pvNewID )
{
Timer_t * const pxTimer = ( Timer_t * ) xTimer;

    configASSERT( xTimer );

    taskENTER_CRITICAL();
    {
        pxTimer->pvTimerID = pvNewID;
    }
    taskEXIT_CRITICAL();
}
/*-----------------------------------------------------------*/

#if( INCLUDE_xTimerPendFunctionCall == 1 )

    BaseType_t xTimerPendFunctionCallFromISR( PendedFunction_t xFunctionToPend, void *pvParameter1, uint32_t ulParameter2, BaseType_t *pxHigherPriorityTaskWoken )
    {
    DaemonTaskMessage_t xMessage;
    BaseType_t xReturn;

        /* Complete the message with the function parameters and post it to the
        daemon task. */
        xMessage.xMessageID = tmrCOMMAND_EXECUTE_CALLBACK_FROM_ISR;
        xMessage.u.xCallbackParameters.pxCallbackFunction = xFunctionToPend;
        xMessage.u.xCallbackParameters.pvParameter1 = pvParameter1;
        xMessage.u.xCallbackParameters.ulParameter2 = ulParameter2;

        xReturn = xQueueSendFromISR( xTimerQueue, &xMessage, pxHigherPriorityTaskWoken );

        tracePEND_FUNC_CALL_FROM_ISR( xFunctionToPend, pvParameter1, ulParameter2, xReturn );

        return xReturn;
    }

#endif /* INCLUDE_xTimerPendFunctionCall */
/*-----------------------------------------------------------*/

#if( INCLUDE_xTimerPendFunctionCall == 1 )

    BaseType_t xTimerPendFunctionCall( PendedFunction_t xFunctionToPend, void *pvParameter1, uint32_t ulParameter2, TickType_t xTicksToWait )
    {
    DaemonTaskMessage_t xMessage;
    BaseType_t xReturn;

        /* This function can only be called after a timer has been created or
        after the scheduler has been started because, until then, the timer
        queue does not exist. */
        configASSERT( xTimerQueue );

        /* Complete the message with the function parameters and post it to the
        daemon task. */
        xMessage.xMessageID = tmrCOMMAND_EXECUTE_CALLBACK;
        xMessage.u.xCallbackParameters.pxCallbackFunction = xFunctionToPend;
        xMessage.u.xCallbackParameters.pvParameter1 = pvParameter1;
        xMessage.u.xCallbackParameters.ulParameter2 = ulParameter2;

        xReturn = xQueueSendToBack( xTimerQueue, &xMessage, xTicksToWait );

        tracePEND_FUNC_CALL( xFunctionToPend, pvParameter1, ulParameter2, xReturn );

        return xReturn;
    }

#endif /* INCLUDE_xTimerPendFunctionCall */
/*-----------------------------------------------------------*/

/* This entire source file will be skipped if the application is not configured
to include software timer functionality.  If you want to include software timer
functionality then ensure configUSE_TIMERS is set to 1 in FreeRTOSConfig.h. */
#endif /* configUSE_TIMERS == 1 */