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ulStatsAsPercentage = pxTaskStatusArray[ x ].ulRunTimeCounter / ulTotalRunTime; if( ulStatsAsPercentage > 0UL ) { sprintf( pcWriteBuffer, "%s\t\t%lu\t\t%lu%%\r\n", pxTaskStatusArray[ x ].pcTaskName, pxTaskStatusArray[ x ].ulRunTimeCounter, ulStatsAsPercentage ); } else { // If the percentage is zero here then the task has // consumed less than 1% of the total run time. sprintf( pcWriteBuffer, "%s\t\t%lu\t\t<1%%\r\n", pxTaskStatusArray[ x ].pcTaskName, pxTaskStatusArray[ x ].ulRunTimeCounter ); } pcWriteBuffer += strlen( ( char * ) pcWriteBuffer ); } } //

If configGENERATE_RUN_TIME_STATS is set to 1 in FreeRTOSConfig.h then *pulTotalRunTime is set by uxTaskGetSystemState() to the total run time (as defined by the run time stats clock, see https://www.FreeRTOS.org/rtos-run-time-stats.html) since the target booted. pulTotalRunTime can be set to NULL to omit the total run time information. - - Returns The number of TaskStatus_t structures that were populated by uxTaskGetSystemState(). This should equal the number returned by the uxTaskGetNumberOfTasks() API function, but will be zero if the value passed in the uxArraySize parameter was too small. - void vTaskList(char *pcWriteBuffer) configUSE_TRACE_FACILITY and configUSE_STATS_FORMATTING_FUNCTIONS must both be defined as 1 for this function to be available. See the configuration section of the FreeRTOS.org website for more information. NOTE 1: This function will disable interrupts for its duration. It is not intended for normal application runtime use but as a debug aid. Lists all the current tasks, along with their current state and stack usage high water mark.

Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. Events can be sent to a task using an intermediary object. Examples of such objects are queues, semaphores, mutexes and event groups. Task notifications are a method of sending an event directly to a task without the need for such an intermediary object. A notification sent to a task can optionally perform an action, such as update, overwrite or increment one of the task's notification values. In that way task notifications can be used to send data to a task, or be used as light weight and fast binary or counting semaphores. A notification sent to a task will remain pending until it is cleared by the task calling xTaskNotifyWaitIndexed() or ulTaskNotifyTakeIndexed() (or their un-indexed equivalents). If the task was already in the Blocked state to wait for a notification when the notification arrives then the task will automatically be removed from the Blocked state (unblocked) and the notification cleared. A task can use xTaskNotifyWaitIndexed() to [optionally] block to wait for a notification to be pending, or ulTaskNotifyTakeIndexed() to [optionally] block to wait for a notification value to have a non-zero value. The task does not consume any CPU time while it is in the Blocked state. NOTE Each notification within the array operates independently - a task can only block on one notification within the array at a time and will not be unblocked by a notification sent to any other array index.

Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. xTaskNotifyWait() is the original API function, and remains backward compatible by always operating on the notification value at index 0 in the array. Calling xTaskNotifyWait() is equivalent to calling xTaskNotifyWaitIndexed() with the uxIndexToWaitOn parameter set to 0. - Parameters uxIndexToWaitOn -- The index within the calling task's array of notification values on which the calling task will wait for a notification to be received.

xTaskNotifyWait() does not have this parameter and always waits for notifications on index 0. ulBitsToClearOnEntry -- Bits that are set in ulBitsToClearOnEntry value will be cleared in the calling task's notification value before the task checks to see if any notifications are pending, and optionally blocks if no notifications are pending. Setting ulBitsToClearOnEntry to ULONG_MAX (if limits.h is included) or 0xffffffffUL (if limits.h is not included) will have the effect of resetting the task's notification value to 0. Setting ulBitsToClearOnEntry to 0 will leave the task's notification value unchanged. ulBitsToClearOnExit -- If a notification is pending or received before the calling task exits the xTaskNotifyWait() function then the task's notification value (see the xTaskNotify() API function) is passed out using the pulNotificationValue parameter. Then any bits that are set in ulBitsToClearOnExit will be cleared in the task's notification value (note *pulNotificationValue is set before any bits are cleared). Setting ulBitsToClearOnExit to ULONG_MAX (if limits.h is included) or 0xffffffffUL (if limits.h is not included) will have the effect of resetting the task's notification value to 0 before the function exits. Setting ulBitsToClearOnExit to 0 will leave the task's notification value unchanged when the function exits (in which case the value passed out in pulNotificationValue will match the task's notification value). pulNotificationValue -- Used to pass the task's notification value out of the function. Note the value passed out will not be effected by the clearing of any bits caused by ulBitsToClearOnExit being non-zero.

The maximum amount of time that the task should wait in the Blocked state for a notification to be received, should a notification not already be pending when xTaskNotifyWait() was called. The task will not consume any processing time while it is in the Blocked state. This is specified in kernel ticks, the macro pdMS_TO_TICKS( value_in_ms ) can be used to convert a time specified in milliseconds to a time specified in ticks. - - Returns If a notification was received (including notifications that were already pending when xTaskNotifyWait was called) then pdPASS is returned. Otherwise pdFAIL is returned. - void vTaskGenericNotifyGiveFromISR(TaskHandle_t xTaskToNotify, UBaseType_t uxIndexToNotify, BaseType_t *pxHigherPriorityTaskWoken) A version of xTaskNotifyGiveIndexed() that can be called from an interrupt service routine (ISR).

Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. Events can be sent to a task using an intermediary object. Examples of such objects are queues, semaphores, mutexes and event groups. Task notifications are a method of sending an event directly to a task without the need for such an intermediary object. A notification sent to a task can optionally perform an action, such as update, overwrite or increment one of the task's notification values. In that way task notifications can be used to send data to a task, or be used as light weight and fast binary or counting semaphores. vTaskNotifyGiveIndexedFromISR() is intended for use when task notifications are used as light weight and faster binary or counting semaphore equivalents. Actual FreeRTOS semaphores are given from an ISR using the xSemaphoreGiveFromISR() API function, the equivalent action that instead uses a task notification is vTaskNotifyGiveIndexedFromISR(). When task notifications are being used as a binary or counting semaphore equivalent then the task being notified should wait for the notification using the ulTaskNotifyTakeIndexed() API function rather than the xTaskNotifyWaitIndexed() API function. NOTE Each notification within the array operates independently - a task can only block on one notification within the array at a time and will not be unblocked by a notification sent to any other array index. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. xTaskNotifyFromISR() is the original API function, and remains backward compatible by always operating on the notification value at index 0 within the array. Calling xTaskNotifyGiveFromISR() is equivalent to calling xTaskNotifyGiveIndexedFromISR() with the uxIndexToNotify parameter set to 0. - Parameters xTaskToNotify --

The index within the target task's array of notification values to act upon. For example, setting uxIndexToClear to 1 will clear the state of the notification at index 1 within the array. uxIndexToClear must be less than configTASK_NOTIFICATION_ARRAY_ENTRIES. ulTaskNotifyStateClear() does not have this parameter and always acts on the notification at index 0. - - Returns pdTRUE if the task's notification state was set to eNotWaitingNotification, otherwise pdFALSE. - uint32_t ulTaskGenericNotifyValueClear(TaskHandle_t xTask, UBaseType_t uxIndexToClear, uint32_t ulBitsToClear) See https://www.FreeRTOS.org/RTOS-task-notifications.html for details. configUSE_TASK_NOTIFICATIONS must be undefined or defined as 1 for these functions to be available. Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. ulTaskNotifyValueClearIndexed() clears the bits specified by the ulBitsToClear bit mask in the notification value at array index uxIndexToClear of the task referenced by xTask. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. ulTaskNotifyValueClear() is the original API function, and remains backward compatible by always operating on the notification value at index 0 within the array. Calling ulTaskNotifyValueClear() is equivalent to calling ulTaskNotifyValueClearIndexed() with the uxIndexToClear parameter set to 0. - Parameters xTask -- The handle of the RTOS task that will have bits in one of its notification values cleared. Set xTask to NULL to clear bits in a notification value of the calling task. To obtain a task's handle create the task using xTaskCreate() and make use of the pxCreatedTask parameter, or create the task using xTaskCreateStatic() and store the returned value, or use the task's name in a call to xTaskGetHandle().

The index within the target task's array of notification values in which to clear the bits. uxIndexToClear must be less than configTASK_NOTIFICATION_ARRAY_ENTRIES. ulTaskNotifyValueClear() does not have this parameter and always clears bits in the notification value at index 0. ulBitsToClear -- Bit mask of the bits to clear in the notification value of xTask. Set a bit to 1 to clear the corresponding bits in the task's notification value. Set ulBitsToClear to 0xffffffff (UINT_MAX on 32-bit architectures) to clear the notification value to 0. Set ulBitsToClear to 0 to query the task's notification value without clearing any bits. - - Returns The value of the target task's notification value before the bits specified by ulBitsToClear were cleared. - void vTaskSetTimeOutState(TimeOut_t *const pxTimeOut) Capture the current time for future use with xTaskCheckForTimeOut(). - Parameters pxTimeOut -- Pointer to a timeout object into which the current time is to be captured. The captured time includes the tick count and the number of times the tick count has overflowed since the system first booted. - BaseType_t xTaskCheckForTimeOut(TimeOut_t

Driver library function used to receive uxWantedBytes from an Rx buffer // that is filled by a UART interrupt. If there are not enough bytes in the // Rx buffer then the task enters the Blocked state until it is notified that // more data has been placed into the buffer. If there is still not enough // data then the task re-enters the Blocked state, and xTaskCheckForTimeOut() // is used to re-calculate the Block time to ensure the total amount of time // spent in the Blocked state does not exceed MAX_TIME_TO_WAIT. This // continues until either the buffer contains at least uxWantedBytes bytes, // or the total amount of time spent in the Blocked state reaches // MAX_TIME_TO_WAIT - at which point the task reads however many bytes are // available up to a maximum of uxWantedBytes.

size_t xUART_Receive( uint8_t *pucBuffer, size_t uxWantedBytes ) { size_t uxReceived = 0; TickType_t xTicksToWait = MAX_TIME_TO_WAIT; TimeOut_t xTimeOut; // Initialize xTimeOut. This records the time at which this function // was entered. vTaskSetTimeOutState( &xTimeOut ); // Loop until the buffer contains the wanted number of bytes, or a // timeout occurs. while( UART_bytes_in_rx_buffer( pxUARTInstance ) < uxWantedBytes ) { // The buffer didn't contain enough data so this task is going to // enter the Blocked state. Adjusting xTicksToWait to account for // any time that has been spent in the Blocked state within this // function so far to ensure the total amount of time spent in the // Blocked state does not exceed MAX_TIME_TO_WAIT. if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) != pdFALSE ) { //Timed out before the wanted number of bytes were available, // exit the loop. break; } // Wait for a maximum of xTicksToWait ticks to be notified that the // receive interrupt has placed more data into the buffer. ulTaskNotifyTake( pdTRUE, xTicksToWait ); } // Attempt to read uxWantedBytes from the receive buffer into pucBuffer. // The actual number of bytes read (which might be less than // uxWantedBytes) is returned.

The number of ticks to check for timeout i.e. if pxTicksToWait ticks have passed since pxTimeOut was last updated (either by vTaskSetTimeOutState() or xTaskCheckForTimeOut()), the timeout has occurred. If the timeout has not occurred, pxTicksToWait is updated to reflect the number of remaining ticks. - - Returns If timeout has occurred, pdTRUE is returned. Otherwise pdFALSE is returned and pxTicksToWait is updated to reflect the number of remaining ticks. - BaseType_t xTaskCatchUpTicks(TickType_t xTicksToCatchUp) This function corrects the tick count value after the application code has held interrupts disabled for an extended period resulting in tick interrupts having been missed. This function is similar to vTaskStepTick(), however, unlike vTaskStepTick(), xTaskCatchUpTicks() may move the tick count forward past a time at which a task should be removed from the blocked state. That means tasks may have to be removed from the blocked state as the tick count is moved. - Parameters xTicksToCatchUp -- The number of tick interrupts that have been missed due to interrupts being disabled. Its value is not computed automatically, so must be computed by the application writer. - Returns pdTRUE if moving the tick count forward resulted in a task leaving the blocked state and a context switch being performed. Otherwise pdFALSE.

Structures - struct xTASK_STATUS Used with the uxTaskGetSystemState() function to return the state of each task in the system. Public Members - TaskHandle_t xHandle The handle of the task to which the rest of the information in the structure relates. - const char *pcTaskName A pointer to the task's name. This value will be invalid if the task was deleted since the structure was populated! - UBaseType_t xTaskNumber A number unique to the task. - eTaskState eCurrentState The state in which the task existed when the structure was populated. - UBaseType_t uxCurrentPriority The priority at which the task was running (may be inherited) when the structure was populated. - UBaseType_t uxBasePriority The priority to which the task will return if the task's current priority has been inherited to avoid unbounded priority inversion when obtaining a mutex. Only valid if configUSE_MUTEXES is defined as 1 in FreeRTOSConfig.h. - configRUN_TIME_COUNTER_TYPE ulRunTimeCounter The total run time allocated to the task so far, as defined by the run time stats clock.

- BaseType_t xCoreID Core this task is pinned to (0, 1, or tskNO_AFFINITY). If configNUMBER_OF_CORES == 1, this will always be 0. - TaskHandle_t xHandle Macros - tskIDLE_PRIORITY Defines the priority used by the idle task. This must not be modified. - tskNO_AFFINITY Macro representing and unpinned (i.e., "no affinity") task in xCoreID parameters - taskVALID_CORE_ID(xCoreID) Macro to check if an xCoreID value is valid - Returns pdTRUE if valid, pdFALSE otherwise. - taskYIELD() Macro for forcing a context switch. - taskENTER_CRITICAL(x) Macro to mark the start of a critical code region. Preemptive context switches cannot occur when in a critical region.

This may alter the stack (depending on the portable implementation) so must be used with care! - taskEXIT_CRITICAL_FROM_ISR(x) - taskEXIT_CRITICAL_ISR(x) - taskDISABLE_INTERRUPTS() Macro to disable all maskable interrupts. - taskENABLE_INTERRUPTS() Macro to enable microcontroller interrupts. - taskSCHEDULER_SUSPENDED Definitions returned by xTaskGetSchedulerState(). taskSCHEDULER_SUSPENDED is 0 to generate more optimal code when configASSERT() is defined as the constant is used in assert() statements. - taskSCHEDULER_NOT_STARTED - taskSCHEDULER_RUNNING - xTaskNotifyIndexed(xTaskToNotify, uxIndexToNotify, ulValue, eAction)

configUSE_TASK_NOTIFICATIONS must be undefined or defined as 1 for these functions to be available. Sends a direct to task notification to a task, with an optional value and action. Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. Events can be sent to a task using an intermediary object. Examples of such objects are queues, semaphores, mutexes and event groups. Task notifications are a method of sending an event directly to a task without the need for such an intermediary object. A notification sent to a task can optionally perform an action, such as update, overwrite or increment one of the task's notification values. In that way task notifications can be used to send data to a task, or be used as light weight and fast binary or counting semaphores. A task can use xTaskNotifyWaitIndexed() or ulTaskNotifyTakeIndexed() to [optionally] block to wait for a notification to be pending.

A notification sent to a task will remain pending until it is cleared by the task calling xTaskNotifyWaitIndexed() or ulTaskNotifyTakeIndexed() (or their un-indexed equivalents). If the task was already in the Blocked state to wait for a notification when the notification arrives then the task will automatically be removed from the Blocked state (unblocked) and the notification cleared. NOTE Each notification within the array operates independently - a task can only block on one notification within the array at a time and will not be unblocked by a notification sent to any other array index. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. xTaskNotify() is the original API function, and remains backward compatible by always operating on the notification value at index 0 in the array. Calling xTaskNotify() is equivalent to calling xTaskNotifyIndexed() with the uxIndexToNotify parameter set to 0. eSetBits - The target notification value is bitwise ORed with ulValue. xTaskNotifyIndexed() always returns pdPASS in this case.

If the task being notified did not already have a notification pending at the same array index then the target notification value is set to ulValue and xTaskNotifyIndexed() will return pdPASS. If the task being notified already had a notification pending at the same array index then no action is performed and pdFAIL is returned. eNoAction - The task receives a notification at the specified array index without the notification value at that index being updated. ulValue is not used and xTaskNotifyIndexed() always returns pdPASS in this case. pulPreviousNotificationValue - Can be used to pass out the subject task's notification value before any bits are modified by the notify function. - Parameters xTaskToNotify -- The handle of the task being notified. The handle to a task can be returned from the xTaskCreate() API function used to create the task, and the handle of the currently running task can be obtained by calling xTaskGetCurrentTaskHandle(). uxIndexToNotify -- The index within the target task's array of notification values to which the notification is to be sent. uxIndexToNotify must be less than configTASK_NOTIFICATION_ARRAY_ENTRIES. xTaskNotify() does not have this parameter and always sends notifications to index 0. ulValue -- Data that can be sent with the notification. How the data is used depends on the value of the eAction parameter. eAction -- Specifies how the notification updates the task's notification value, if at all. Valid values for eAction are as follows: - - Returns Dependent on the value of eAction. See the description of the eAction parameter. - xTaskNotifyAndQueryIndexed(xTaskToNotify, uxIndexToNotify, ulValue, eAction, pulPreviousNotifyValue)

xTaskNotifyAndQueryIndexed() performs the same operation as xTaskNotifyIndexed() with the addition that it also returns the subject task's prior notification value (the notification value at the time the function is called rather than when the function returns) in the additional pulPreviousNotifyValue parameter. xTaskNotifyAndQuery() performs the same operation as xTaskNotify() with the addition that it also returns the subject task's prior notification value (the notification value as it was at the time the function is called, rather than when the function returns) in the additional pulPreviousNotifyValue parameter. - xTaskNotifyIndexedFromISR(xTaskToNotify, uxIndexToNotify, ulValue, eAction, pxHigherPriorityTaskWoken)

A version of xTaskNotifyIndexed() that can be used from an interrupt service routine (ISR). Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. Events can be sent to a task using an intermediary object. Examples of such objects are queues, semaphores, mutexes and event groups. Task notifications are a method of sending an event directly to a task without the need for such an intermediary object. A notification sent to a task can optionally perform an action, such as update, overwrite or increment one of the task's notification values. In that way task notifications can be used to send data to a task, or be used as light weight and fast binary or counting semaphores. A task can use xTaskNotifyWaitIndexed() to [optionally] block to wait for a notification to be pending, or ulTaskNotifyTakeIndexed() to [optionally] block to wait for a notification value to have a non-zero value. The task does not consume any CPU time while it is in the Blocked state.

A notification sent to a task will remain pending until it is cleared by the task calling xTaskNotifyWaitIndexed() or ulTaskNotifyTakeIndexed() (or their un-indexed equivalents). If the task was already in the Blocked state to wait for a notification when the notification arrives then the task will automatically be removed from the Blocked state (unblocked) and the notification cleared. NOTE Each notification within the array operates independently - a task can only block on one notification within the array at a time and will not be unblocked by a notification sent to any other array index. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. xTaskNotifyFromISR() is the original API function, and remains backward compatible by always operating on the notification value at index 0 within the array. Calling xTaskNotifyFromISR() is equivalent to calling xTaskNotifyIndexedFromISR() with the uxIndexToNotify parameter set to 0. eSetBits - The task's notification value is bitwise ORed with ulValue. xTaskNotify() always returns pdPASS in this case. eIncrement - The task's notification value is incremented. ulValue is not used and xTaskNotify() always returns pdPASS in this case.

If the task being notified did not already have a notification pending then the task's notification value is set to ulValue and xTaskNotify() will return pdPASS. If the task being notified already had a notification pending then no action is performed and pdFAIL is returned. eNoAction - The task receives a notification without its notification value being updated. ulValue is not used and xTaskNotify() always returns pdPASS in this case. - Parameters uxIndexToNotify -- The index within the target task's array of notification values to which the notification is to be sent. uxIndexToNotify must be less than configTASK_NOTIFICATION_ARRAY_ENTRIES. xTaskNotifyFromISR() does not have this parameter and always sends notifications to index 0.

The handle of the task being notified. The handle to a task can be returned from the xTaskCreate() API function used to create the task, and the handle of the currently running task can be obtained by calling xTaskGetCurrentTaskHandle(). ulValue -- Data that can be sent with the notification. How the data is used depends on the value of the eAction parameter. eAction -- Specifies how the notification updates the task's notification value, if at all. Valid values for eAction are as follows: pxHigherPriorityTaskWoken -- xTaskNotifyFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if sending the notification caused the task to which the notification was sent to leave the Blocked state, and the unblocked task has a priority higher than the currently running task. If xTaskNotifyFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited. How a context switch is requested from an ISR is dependent on the port - see the documentation page for the port in use. - - Returns Dependent on the value of eAction. See the description of the eAction parameter. - xTaskNotifyAndQueryIndexedFromISR(xTaskToNotify, uxIndexToNotify, ulValue, eAction, pulPreviousNotificationValue, pxHigherPriorityTaskWoken)

xTaskNotifyAndQueryIndexedFromISR() performs the same operation as xTaskNotifyIndexedFromISR() with the addition that it also returns the subject task's prior notification value (the notification value at the time the function is called rather than at the time the function returns) in the additional pulPreviousNotifyValue parameter. xTaskNotifyAndQueryFromISR() performs the same operation as xTaskNotifyFromISR() with the addition that it also returns the subject task's prior notification value (the notification value at the time the function is called rather than at the time the function returns) in the additional pulPreviousNotifyValue parameter. - xTaskNotifyWait(ulBitsToClearOnEntry, ulBitsToClearOnExit, pulNotificationValue, xTicksToWait) - xTaskNotifyWaitIndexed(uxIndexToWaitOn, ulBitsToClearOnEntry, ulBitsToClearOnExit, pulNotificationValue, xTicksToWait) - xTaskNotifyGiveIndexed(xTaskToNotify, uxIndexToNotify) Sends a direct to task notification to a particular index in the target task's notification array in a manner similar to giving a counting semaphore.

Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. Events can be sent to a task using an intermediary object. Examples of such objects are queues, semaphores, mutexes and event groups. Task notifications are a method of sending an event directly to a task without the need for such an intermediary object. A notification sent to a task can optionally perform an action, such as update, overwrite or increment one of the task's notification values. In that way task notifications can be used to send data to a task, or be used as light weight and fast binary or counting semaphores. xTaskNotifyGiveIndexed() is a helper macro intended for use when task notifications are used as light weight and faster binary or counting semaphore equivalents. Actual FreeRTOS semaphores are given using the xSemaphoreGive() API function, the equivalent action that instead uses a task notification is xTaskNotifyGiveIndexed(). When task notifications are being used as a binary or counting semaphore equivalent then the task being notified should wait for the notification using the ulTaskNotifyTakeIndexed() API function rather than the xTaskNotifyWaitIndexed() API function. NOTE Each notification within the array operates independently - a task can only block on one notification within the array at a time and will not be unblocked by a notification sent to any other array index. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. xTaskNotifyGive() is the original API function, and remains backward compatible by always operating on the notification value at index 0 in the array. Calling xTaskNotifyGive() is equivalent to calling xTaskNotifyGiveIndexed() with the uxIndexToNotify parameter set to 0. - Parameters xTaskToNotify --

The maximum amount of time the task should block waiting for space to become available on the queue, should it already be full. The call will return immediately if this is set to 0 and the queue is full. The time is defined in tick periods so the constant portTICK_PERIOD_MS should be used to convert to real time if this is required. xCopyPosition -- Can take the value queueSEND_TO_BACK to place the item at the back of the queue, or queueSEND_TO_FRONT to place the item at the front of the queue (for high priority messages). - - Returns pdTRUE if the item was successfully posted, otherwise errQUEUE_FULL. - BaseType_t xQueuePeek(QueueHandle_t xQueue, void *const pvBuffer, TickType_t xTicksToWait) Receive an item from a queue without removing the item from the queue. The item is received by copy so a buffer of adequate size must be provided. The number of bytes copied into the buffer was defined when the queue was created. Successfully received items remain on the queue so will be returned again by the next call, or a call to xQueueReceive(). This macro must not be used in an interrupt service routine. See xQueuePeekFromISR() for an alternative that can be called from an interrupt service routine. Example usage: struct AMessage { char ucMessageID; char ucData[ 20 ]; } xMessage; QueueHandle_t xQueue; // Task to create a queue and post a value.

The maximum amount of time the task should block waiting for an item to receive should the queue be empty at the time of the call. The time is defined in tick periods so the constant portTICK_PERIOD_MS should be used to convert to real time if this is required. xQueuePeek() will return immediately if xTicksToWait is 0 and the queue is empty. - - Returns pdTRUE if an item was successfully received from the queue, otherwise pdFALSE. - BaseType_t xQueuePeekFromISR(QueueHandle_t xQueue, void *const pvBuffer) A version of xQueuePeek() that can be called from an interrupt service routine (ISR). Receive an item from a queue without removing the item from the queue. The item is received by copy so a buffer of adequate size must be provided. The number of bytes copied into the buffer was defined when the queue was created. Successfully received items remain on the queue so will be returned again by the next call, or a call to xQueueReceive(). - Parameters xQueue -- The handle to the queue from which the item is to be received. pvBuffer -- Pointer to the buffer into which the received item will be copied. - - Returns pdTRUE if an item was successfully received from the queue, otherwise pdFALSE. - BaseType_t xQueueReceive(QueueHandle_t xQueue, void *const pvBuffer, TickType_t xTicksToWait) Receive an item from a queue. The item is received by copy so a buffer of adequate size must be provided. The number of bytes copied into the buffer was defined when the queue was created. Successfully received items are removed from the queue. This function must not be used in an interrupt service routine. See xQueueReceiveFromISR for an alternative that can. Example usage: struct AMessage { char ucMessageID; char ucData[ 20 ]; } xMessage; QueueHandle_t xQueue; // Task to create a queue and post a value.

The maximum amount of time the task should block waiting for an item to receive should the queue be empty at the time of the call. xQueueReceive() will return immediately if xTicksToWait is zero and the queue is empty. The time is defined in tick periods so the constant portTICK_PERIOD_MS should be used to convert to real time if this is required. - - Returns pdTRUE if an item was successfully received from the queue, otherwise pdFALSE. - UBaseType_t uxQueueMessagesWaiting(const QueueHandle_t xQueue) Return the number of messages stored in a queue. - Parameters xQueue -- A handle to the queue being queried. - Returns The number of messages available in the queue. - UBaseType_t uxQueueSpacesAvailable(const QueueHandle_t xQueue) Return the number of free spaces available in a queue. This is equal to the number of items that can be sent to the queue before the queue becomes full if no items are removed. - Parameters xQueue -- A handle to the queue being queried. - Returns The number of spaces available in the queue. - void vQueueDelete(QueueHandle_t xQueue) Delete a queue - freeing all the memory allocated for storing of items placed on the queue. - Parameters xQueue -- A handle to the queue to be deleted. - BaseType_t xQueueGenericSendFromISR(QueueHandle_t xQueue, const void *const pvItemToQueue, BaseType_t *const pxHigherPriorityTaskWoken, const BaseType_t xCopyPosition) It is preferred that the macros xQueueSendFromISR(), xQueueSendToFrontFromISR() and xQueueSendToBackFromISR() be used in place of calling this function directly. xQueueGiveFromISR() is an equivalent for use by semaphores that don't actually copy any data. Post an item on a queue. It is safe to use this function from within an interrupt service routine. Items are queued by copy not reference so it is preferable to only queue small items, especially when called from an ISR. In most cases it would be preferable to store a pointer to the item being queued. Example usage for buffered IO (where the ISR can obtain more than one value per call): void vBufferISR( void ) { char cIn; BaseType_t xHigherPriorityTaskWokenByPost; // We have not woken a task at the start of the ISR. xHigherPriorityTaskWokenByPost = pdFALSE; // Loop until the buffer is empty. do { // Obtain a byte from the buffer. cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS ); // Post each byte. xQueueGenericSendFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWokenByPost, queueSEND_TO_BACK ); } while( portINPUT_BYTE( BUFFER_COUNT ) ); // Now the buffer is empty we can switch context if necessary. Note that the // name of the yield function required is port specific. if( xHigherPriorityTaskWokenByPost ) { portYIELD_FROM_ISR(); } } - Parameters xQueue -- The handle to the queue on which the item is to be posted.

A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area. pxHigherPriorityTaskWoken -- xQueueGenericSendFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if sending to the queue caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If xQueueGenericSendFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited. xCopyPosition -- Can take the value queueSEND_TO_BACK to place the item at the back of the queue, or queueSEND_TO_FRONT to place the item at the front of the queue (for high priority messages). - - Returns pdTRUE if the data was successfully sent to the queue, otherwise errQUEUE_FULL. - BaseType_t xQueueGiveFromISR(QueueHandle_t xQueue, BaseType_t *const pxHigherPriorityTaskWoken) - BaseType_t xQueueReceiveFromISR(QueueHandle_t xQueue, void *const pvBuffer, BaseType_t *const pxHigherPriorityTaskWoken) Receive an item from a queue. It is safe to use this function from within an interrupt service routine. Example usage: QueueHandle_t xQueue; // Function to create a queue and post some values.

{ // A character was received. Output the character now. vOutputCharacter( cRxedChar ); // If removing the character from the queue woke the task that was // posting onto the queue xTaskWokenByReceive will have been set to // pdTRUE. No matter how many times this loop iterates only one // task will be woken. } if( xTaskWokenByReceive != ( char ) pdFALSE; { taskYIELD (); } } - Parameters xQueue -- The handle to the queue from which the item is to be received. pvBuffer -- Pointer to the buffer into which the received item will be copied.

A task may be blocked waiting for space to become available on the queue. If xQueueReceiveFromISR causes such a task to unblock *pxTaskWoken will get set to pdTRUE, otherwise *pxTaskWoken will remain unchanged. - - Returns pdTRUE if an item was successfully received from the queue, otherwise pdFALSE. - BaseType_t xQueueIsQueueEmptyFromISR(const QueueHandle_t xQueue) Queries a queue to determine if the queue is empty. This function should only be used in an ISR. - Parameters xQueue -- The handle of the queue being queried - Returns pdFALSE if the queue is not empty, or pdTRUE if the queue is empty. - BaseType_t xQueueIsQueueFullFromISR(const QueueHandle_t xQueue) Queries a queue to determine if the queue is full. This function should only be used in an ISR. - Parameters xQueue -- The handle of the queue being queried - Returns pdFALSE if the queue is not full, or pdTRUE if the queue is full. - UBaseType_t uxQueueMessagesWaitingFromISR(const QueueHandle_t xQueue) A version of uxQueueMessagesWaiting() that can be called from an ISR. Return the number of messages stored in a queue. - Parameters xQueue -- A handle to the queue being queried. - Returns The number of messages available in the queue. - void vQueueAddToRegistry(QueueHandle_t xQueue, const char *pcQueueName) The registry is provided as a means for kernel aware debuggers to locate queues, semaphores and mutexes. Call vQueueAddToRegistry() add a queue, semaphore or mutex handle to the registry if you want the handle to be available to a kernel aware debugger. If you are not using a kernel aware debugger then this function can be ignored. configQUEUE_REGISTRY_SIZE defines the maximum number of handles the registry can hold. configQUEUE_REGISTRY_SIZE must be greater than 0 within FreeRTOSConfig.h for the registry to be available. Its value does not affect the number of queues, semaphores and mutexes that can be created - just the number that the registry can hold. If vQueueAddToRegistry is called more than once with the same xQueue parameter, the registry will store the pcQueueName parameter from the most recent call to vQueueAddToRegistry. - Parameters xQueue -- The handle of the queue being added to the registry. This is the handle returned by a call to xQueueCreate(). Semaphore and mutex handles can also be passed in here.

The name to be associated with the handle. This is the name that the kernel aware debugger will display. The queue registry only stores a pointer to the string - so the string must be persistent (global or preferably in ROM/Flash), not on the stack. - - void vQueueUnregisterQueue(QueueHandle_t xQueue) The registry is provided as a means for kernel aware debuggers to locate queues, semaphores and mutexes. Call vQueueAddToRegistry() add a queue, semaphore or mutex handle to the registry if you want the handle to be available to a kernel aware debugger, and vQueueUnregisterQueue() to remove the queue, semaphore or mutex from the register. If you are not using a kernel aware debugger then this function can be ignored. - Parameters xQueue -- The handle of the queue being removed from the registry. - const char *pcQueueGetName(QueueHandle_t xQueue) The queue registry is provided as a means for kernel aware debuggers to locate queues, semaphores and mutexes. Call pcQueueGetName() to look up and return the name of a queue in the queue registry from the queue's handle. - Parameters xQueue -- The handle of the queue the name of which will be returned. - Returns If the queue is in the registry then a pointer to the name of the queue is returned. If the queue is not in the registry then NULL is returned. - QueueSetHandle_t xQueueCreateSet(const UBaseType_t uxEventQueueLength) Queue sets provide a mechanism to allow a task to block (pend) on a read operation from multiple queues or semaphores simultaneously.

A queue set must be explicitly created using a call to xQueueCreateSet() before it can be used. Once created, standard FreeRTOS queues and semaphores can be added to the set using calls to xQueueAddToSet(). xQueueSelectFromSet() is then used to determine which, if any, of the queues or semaphores contained in the set is in a state where a queue read or semaphore take operation would be successful. Note 1: See the documentation on https://www.FreeRTOS.org/RTOS-queue-sets.html for reasons why queue sets are very rarely needed in practice as there are simpler methods of blocking on multiple objects. Note 2: Blocking on a queue set that contains a mutex will not cause the mutex holder to inherit the priority of the blocked task. Note 3: An additional 4 bytes of RAM is required for each space in a every queue added to a queue set. Therefore counting semaphores that have a high maximum count value should not be added to a queue set. Note 4: A receive (in the case of a queue) or take (in the case of a semaphore) operation must not be performed on a member of a queue set unless a call to xQueueSelectFromSet() has first returned a handle to that set member. - Parameters uxEventQueueLength -- Queue sets store events that occur on the queues and semaphores contained in the set. uxEventQueueLength specifies the maximum number of events that can be queued at once. To be absolutely certain that events are not lost uxEventQueueLength should be set to the total sum of the length of the queues added to the set, where binary semaphores and mutexes have a length of 1, and counting semaphores have a length set by their maximum count value. Examples: If a queue set is to hold a queue of length 5, another queue of length 12, and a binary semaphore, then uxEventQueueLength should be set to (5 + 12 + 1), or 18. If a queue set is to hold three binary semaphores then uxEventQueueLength should be set to (1 + 1 + 1 ), or 3. If a queue set is to hold a counting semaphore that has a maximum count of 5, and a counting semaphore that has a maximum count of 3, then uxEventQueueLength should be set to (5 + 3), or 8. - - Returns If the queue set is created successfully then a handle to the created queue set is returned. Otherwise NULL is returned. - BaseType_t xQueueAddToSet(QueueSetMemberHandle_t xQueueOrSemaphore, QueueSetHandle_t xQueueSet) Adds a queue or semaphore to a queue set that was previously created by a call to xQueueCreateSet(). See FreeRTOS/Source/Demo/Common/Minimal/QueueSet.c for an example using this function. Note 1: A receive (in the case of a queue) or take (in the case of a semaphore) operation must not be performed on a member of a queue set unless a call to xQueueSelectFromSet() has first returned a handle to that set member. - Parameters xQueueOrSemaphore -- The handle of the queue or semaphore being added to the queue set (cast to an QueueSetMemberHandle_t type).

The handle of the queue set to which the queue or semaphore is being added. - - Returns If the queue or semaphore was successfully added to the queue set then pdPASS is returned. If the queue could not be successfully added to the queue set because it is already a member of a different queue set then pdFAIL is returned . - BaseType_t xQueueRemoveFromSet(QueueSetMemberHandle_t xQueueOrSemaphore, QueueSetHandle_t xQueueSet) Removes a queue or semaphore from a queue set. A queue or semaphore can only be removed from a set if the queue or semaphore is empty. See FreeRTOS/Source/Demo/Common/Minimal/QueueSet.c for an example using this function. - Parameters xQueueOrSemaphore -- The handle of the queue or semaphore being removed from the queue set (cast to an QueueSetMemberHandle_t type).

The handle of the queue set in which the queue or semaphore is included. - - Returns If the queue or semaphore was successfully removed from the queue set then pdPASS is returned. If the queue was not in the queue set, or the queue (or semaphore) was not empty, then pdFAIL is returned. - QueueSetMemberHandle_t xQueueSelectFromSet(QueueSetHandle_t xQueueSet, const TickType_t xTicksToWait) xQueueSelectFromSet() selects from the members of a queue set a queue or semaphore that either contains data (in the case of a queue) or is available to take (in the case of a semaphore). xQueueSelectFromSet() effectively allows a task to block (pend) on a read operation on all the queues and semaphores in a queue set simultaneously. See FreeRTOS/Source/Demo/Common/Minimal/QueueSet.c for an example using this function. Note 1: See the documentation on https://www.FreeRTOS.org/RTOS-queue-sets.html for reasons why queue sets are very rarely needed in practice as there are simpler methods of blocking on multiple objects. Note 2: Blocking on a queue set that contains a mutex will not cause the mutex holder to inherit the priority of the blocked task. Note 3: A receive (in the case of a queue) or take (in the case of a semaphore) operation must not be performed on a member of a queue set unless a call to xQueueSelectFromSet() has first returned a handle to that set member. - Parameters xQueueSet -- The queue set on which the task will (potentially) block.

The maximum time, in ticks, that the calling task will remain in the Blocked state (with other tasks executing) to wait for a member of the queue set to be ready for a successful queue read or semaphore take operation. - - Returns xQueueSelectFromSet() will return the handle of a queue (cast to a QueueSetMemberHandle_t type) contained in the queue set that contains data, or the handle of a semaphore (cast to a QueueSetMemberHandle_t type) contained in the queue set that is available, or NULL if no such queue or semaphore exists before before the specified block time expires. - QueueSetMemberHandle_t xQueueSelectFromSetFromISR(QueueSetHandle_t xQueueSet) A version of xQueueSelectFromSet() that can be used from an ISR. Macros - xQueueCreate(uxQueueLength, uxItemSize) Creates a new queue instance, and returns a handle by which the new queue can be referenced. Internally, within the FreeRTOS implementation, queues use two blocks of memory. The first block is used to hold the queue's data structures. The second block is used to hold items placed into the queue. If a queue is created using xQueueCreate() then both blocks of memory are automatically dynamically allocated inside the xQueueCreate() function. (see https://www.FreeRTOS.org/a00111.html).

If a queue is created using xQueueCreateStatic() then the application writer must provide the memory that will get used by the queue. xQueueCreateStatic() therefore allows a queue to be created without using any dynamic memory allocation. https://www.FreeRTOS.org/Embedded-RTOS-Queues.html Example usage: struct AMessage { char ucMessageID; char ucData[ 20 ]; }; void vATask( void *pvParameters ) { QueueHandle_t xQueue1, xQueue2; // Create a queue capable of containing 10 uint32_t values. xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) ); if( xQueue1 == 0 ) { // Queue was not created and must not be used. } // Create a queue capable of containing 10 pointers to AMessage structures.

The number of bytes each item in the queue will require. Items are queued by copy, not by reference, so this is the number of bytes that will be copied for each posted item. Each item on the queue must be the same size. - - Returns If the queue is successfully create then a handle to the newly created queue is returned. If the queue cannot be created then 0 is returned. - xQueueCreateStatic(uxQueueLength, uxItemSize, pucQueueStorage, pxQueueBuffer) Creates a new queue instance, and returns a handle by which the new queue can be referenced. Internally, within the FreeRTOS implementation, queues use two blocks of memory. The first block is used to hold the queue's data structures. The second block is used to hold items placed into the queue. If a queue is created using xQueueCreate() then both blocks of memory are automatically dynamically allocated inside the xQueueCreate() function. (see https://www.FreeRTOS.org/a00111.html).

If a queue is created using xQueueCreateStatic() then the application writer must provide the memory that will get used by the queue. xQueueCreateStatic() therefore allows a queue to be created without using any dynamic memory allocation. https://www.FreeRTOS.org/Embedded-RTOS-Queues.html Example usage: struct AMessage { char ucMessageID; char ucData[ 20 ]; }; #define QUEUE_LENGTH 10 #define ITEM_SIZE sizeof( uint32_t ) // xQueueBuffer will hold the queue structure. StaticQueue_t xQueueBuffer; // ucQueueStorage will hold the items posted to the queue. Must be at least //

The number of bytes each item in the queue will require. Items are queued by copy, not by reference, so this is the number of bytes that will be copied for each posted item. Each item on the queue must be the same size. pucQueueStorage -- If uxItemSize is not zero then pucQueueStorage must point to a uint8_t array that is at least large enough to hold the maximum number of items that can be in the queue at any one time - which is ( uxQueueLength * uxItemsSize ) bytes. If uxItemSize is zero then pucQueueStorage can be NULL. pxQueueBuffer -- Must point to a variable of type StaticQueue_t, which will be used to hold the queue's data structure. - - Returns If the queue is created then a handle to the created queue is returned. If pxQueueBuffer is NULL then NULL is returned. - xQueueGetStaticBuffers(xQueue, ppucQueueStorage, ppxStaticQueue) Retrieve pointers to a statically created queue's data structure buffer and storage area buffer. These are the same buffers that are supplied at the time of creation. - Parameters xQueue -- The queue for which to retrieve the buffers. ppucQueueStorage -- Used to return a pointer to the queue's storage area buffer. ppxStaticQueue -- Used to return a pointer to the queue's data structure buffer. - - Returns pdTRUE if buffers were retrieved, pdFALSE otherwise. - xQueueSendToFront(xQueue, pvItemToQueue, xTicksToWait) Post an item to the front of a queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueSendFromISR () for an alternative which may be used in an ISR. Example usage: struct AMessage { char ucMessageID; char ucData[ 20 ]; } xMessage; uint32_t ulVar = 10UL; void vATask( void *pvParameters ) { QueueHandle_t xQueue1, xQueue2; struct AMessage *pxMessage; // Create a queue capable of containing 10 uint32_t values. xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) ); // Create a queue capable of containing 10 pointers to AMessage structures. // These should be passed by pointer as they contain a lot of data. xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) ); // ... if( xQueue1 != 0 ) { // Send an uint32_t.

The maximum amount of time the task should block waiting for space to become available on the queue, should it already be full. The call will return immediately if this is set to 0 and the queue is full. The time is defined in tick periods so the constant portTICK_PERIOD_MS should be used to convert to real time if this is required. - - Returns pdTRUE if the item was successfully posted, otherwise errQUEUE_FULL. - xQueueSendToBack(xQueue, pvItemToQueue, xTicksToWait) This is a macro that calls xQueueGenericSend(). Post an item to the back of a queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueSendFromISR () for an alternative which may be used in an ISR. Example usage: struct AMessage { char ucMessageID; char ucData[ 20 ]; } xMessage; uint32_t ulVar = 10UL; void vATask( void *pvParameters ) { QueueHandle_t xQueue1, xQueue2; struct AMessage *pxMessage; // Create a queue capable of containing 10 uint32_t values. xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) ); // Create a queue capable of containing 10 pointers to AMessage structures. // These should be passed by pointer as they contain a lot of data. xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) ); // ... if( xQueue1 != 0 ) { // Send an uint32_t.

The maximum amount of time the task should block waiting for space to become available on the queue, should it already be full. The call will return immediately if this is set to 0 and the queue is full. The time is defined in tick periods so the constant portTICK_PERIOD_MS should be used to convert to real time if this is required. - - Returns pdTRUE if the item was successfully posted, otherwise errQUEUE_FULL. - xQueueSend(xQueue, pvItemToQueue, xTicksToWait) This is a macro that calls xQueueGenericSend(). It is included for backward compatibility with versions of FreeRTOS.org that did not include the xQueueSendToFront() and xQueueSendToBack() macros. It is equivalent to xQueueSendToBack(). Post an item on a queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueSendFromISR () for an alternative which may be used in an ISR. Example usage: struct AMessage { char ucMessageID; char ucData[ 20 ]; } xMessage; uint32_t ulVar = 10UL; void vATask( void *pvParameters ) { QueueHandle_t xQueue1, xQueue2; struct AMessage *pxMessage; // Create a queue capable of containing 10 uint32_t values. xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) ); // Create a queue capable of containing 10 pointers to AMessage structures. // These should be passed by pointer as they contain a lot of data. xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) ); // ... if( xQueue1 != 0 ) { // Send an uint32_t.

The maximum amount of time the task should block waiting for space to become available on the queue, should it already be full. The call will return immediately if this is set to 0 and the queue is full. The time is defined in tick periods so the constant portTICK_PERIOD_MS should be used to convert to real time if this is required. - - Returns pdTRUE if the item was successfully posted, otherwise errQUEUE_FULL. - xQueueOverwrite(xQueue, pvItemToQueue) Only for use with queues that have a length of one - so the queue is either empty or full. Post an item on a queue. If the queue is already full then overwrite the value held in the queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueOverwriteFromISR () for an alternative which may be used in an ISR. Example usage: void vFunction( void *pvParameters ) { QueueHandle_t xQueue; uint32_t ulVarToSend, ulValReceived; // Create a queue to hold one uint32_t value. It is strongly // recommended *not* to use xQueueOverwrite() on queues that can // contain more than one value, and doing so will trigger an assertion // if configASSERT() is defined. xQueue = xQueueCreate( 1, sizeof( uint32_t ) ); // Write the value 10 to the queue using xQueueOverwrite(). ulVarToSend = 10; xQueueOverwrite( xQueue, &ulVarToSend ); // Peeking the queue should now return 10, but leave the value 10 in // the queue. A block time of zero is used as it is known that the // queue holds a value. ulValReceived = 0; xQueuePeek( xQueue, &ulValReceived, 0 ); if( ulValReceived != 10 ) { // Error unless the item was removed by a different task. } //

A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area. - - Returns xQueueOverwrite() is a macro that calls xQueueGenericSend(), and therefore has the same return values as xQueueSendToFront(). However, pdPASS is the only value that can be returned because xQueueOverwrite() will write to the queue even when the queue is already full. - xQueueSendToFrontFromISR(xQueue, pvItemToQueue, pxHigherPriorityTaskWoken) This is a macro that calls xQueueGenericSendFromISR(). Post an item to the front of a queue. It is safe to use this macro from within an interrupt service routine. Items are queued by copy not reference so it is preferable to only queue small items, especially when called from an ISR. In most cases it would be preferable to store a pointer to the item being queued. Example usage for buffered IO (where the ISR can obtain more than one value per call): void vBufferISR( void ) { char cIn; BaseType_t xHigherPriorityTaskWoken; // We have not woken a task at the start of the ISR. xHigherPriorityTaskWoken = pdFALSE; // Loop until the buffer is empty. do { // Obtain a byte from the buffer. cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS ); // Post the byte. xQueueSendToFrontFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken ); } while( portINPUT_BYTE( BUFFER_COUNT ) ); // Now the buffer is empty we can switch context if necessary. if( xHigherPriorityTaskWoken ) { taskYIELD (); } } - Parameters xQueue -- The handle to the queue on which the item is to be posted.

A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area. pxHigherPriorityTaskWoken -- xQueueSendToFrontFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if sending to the queue caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If xQueueSendToFromFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited. - - Returns pdTRUE if the data was successfully sent to the queue, otherwise errQUEUE_FULL. - xQueueSendToBackFromISR(xQueue, pvItemToQueue, pxHigherPriorityTaskWoken) This is a macro that calls xQueueGenericSendFromISR(). Post an item to the back of a queue. It is safe to use this macro from within an interrupt service routine. Items are queued by copy not reference so it is preferable to only queue small items, especially when called from an ISR. In most cases it would be preferable to store a pointer to the item being queued. Example usage for buffered IO (where the ISR can obtain more than one value per call): void vBufferISR( void ) { char cIn; BaseType_t xHigherPriorityTaskWoken; // We have not woken a task at the start of the ISR. xHigherPriorityTaskWoken = pdFALSE; // Loop until the buffer is empty. do { // Obtain a byte from the buffer. cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS ); // Post the byte. xQueueSendToBackFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken ); } while( portINPUT_BYTE( BUFFER_COUNT ) ); // Now the buffer is empty we can switch context if necessary. if( xHigherPriorityTaskWoken ) { taskYIELD (); } } - Parameters xQueue -- The handle to the queue on which the item is to be posted.

A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area. pxHigherPriorityTaskWoken -- xQueueSendToBackFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if sending to the queue caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If xQueueSendToBackFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited. - - Returns pdTRUE if the data was successfully sent to the queue, otherwise errQUEUE_FULL. - xQueueOverwriteFromISR(xQueue, pvItemToQueue, pxHigherPriorityTaskWoken) A version of xQueueOverwrite() that can be used in an interrupt service routine (ISR). Only for use with queues that can hold a single item - so the queue is either empty or full. Post an item on a queue. If the queue is already full then overwrite the value held in the queue. The item is queued by copy, not by reference. Example usage: QueueHandle_t xQueue; void vFunction( void *pvParameters ) { // Create a queue to hold one uint32_t value. It is strongly // recommended *not* to use xQueueOverwriteFromISR() on queues that can // contain more than one value, and doing so will trigger an assertion // if configASSERT() is defined. xQueue = xQueueCreate( 1, sizeof( uint32_t ) ); } void vAnInterruptHandler( void ) { // xHigherPriorityTaskWoken must be set to pdFALSE before it is used. BaseType_t xHigherPriorityTaskWoken = pdFALSE; uint32_t ulVarToSend, ulValReceived; // Write the value 10 to the queue using xQueueOverwriteFromISR(). ulVarToSend = 10; xQueueOverwriteFromISR( xQueue, &ulVarToSend, &xHigherPriorityTaskWoken ); // The queue is full, but calling xQueueOverwriteFromISR() again will still // pass because the value held in the queue will be overwritten with the // new value. ulVarToSend = 100; xQueueOverwriteFromISR( xQueue, &ulVarToSend, &xHigherPriorityTaskWoken ); // Reading from the queue will now return 100. // ... if( xHigherPrioritytaskWoken == pdTRUE ) { // Writing to the queue caused a task to unblock and the unblocked task // has a priority higher than or equal to the priority of the currently // executing task (the task this interrupt interrupted). Perform a context // switch so this interrupt returns directly to the unblocked task.

A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area. pxHigherPriorityTaskWoken -- xQueueOverwriteFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if sending to the queue caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If xQueueOverwriteFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited. - - Returns xQueueOverwriteFromISR() is a macro that calls xQueueGenericSendFromISR(), and therefore has the same return values as xQueueSendToFrontFromISR(). However, pdPASS is the only value that can be returned because xQueueOverwriteFromISR() will write to the queue even when the queue is already full. - xQueueSendFromISR(xQueue, pvItemToQueue, pxHigherPriorityTaskWoken) This is a macro that calls xQueueGenericSendFromISR(). It is included for backward compatibility with versions of FreeRTOS.org that did not include the xQueueSendToBackFromISR() and xQueueSendToFrontFromISR() macros. Post an item to the back of a queue. It is safe to use this function from within an interrupt service routine. Items are queued by copy not reference so it is preferable to only queue small items, especially when called from an ISR. In most cases it would be preferable to store a pointer to the item being queued. Example usage for buffered IO (where the ISR can obtain more than one value per call): void vBufferISR( void ) { char cIn; BaseType_t xHigherPriorityTaskWoken; // We have not woken a task at the start of the ISR. xHigherPriorityTaskWoken = pdFALSE; // Loop until the buffer is empty. do { // Obtain a byte from the buffer. cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS ); // Post the byte. xQueueSendFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken ); } while( portINPUT_BYTE( BUFFER_COUNT ) ); // Now the buffer is empty we can switch context if necessary. if( xHigherPriorityTaskWoken ) { // Actual macro used here is port specific. portYIELD_FROM_ISR (); } } - Parameters xQueue -- The handle to the queue on which the item is to be posted.

A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area. pxHigherPriorityTaskWoken -- xQueueSendFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if sending to the queue caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If xQueueSendFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited. - - Returns pdTRUE if the data was successfully sent to the queue, otherwise errQUEUE_FULL. - xQueueReset(xQueue) Reset a queue back to its original empty state. The return value is now obsolete and is always set to pdPASS. Type Definitions - typedef struct QueueDefinition *QueueHandle_t - typedef struct QueueDefinition *QueueSetHandle_t Type by which queue sets are referenced. For example, a call to xQueueCreateSet() returns an xQueueSet variable that can then be used as a parameter to xQueueSelectFromSet(), xQueueAddToSet(), etc. - typedef struct QueueDefinition *QueueSetMemberHandle_t Queue sets can contain both queues and semaphores, so the QueueSetMemberHandle_t is defined as a type to be used where a parameter or return value can be either an QueueHandle_t or an SemaphoreHandle_t. Semaphore API Header File components/freertos/FreeRTOS-Kernel/include/freertos/semphr.h This header file can be included with: #include "freertos/semphr.h" Macros - semBINARY_SEMAPHORE_QUEUE_LENGTH - semSEMAPHORE_QUEUE_ITEM_LENGTH - semGIVE_BLOCK_TIME - vSemaphoreCreateBinary(xSemaphore)

In many usage scenarios it is faster and more memory efficient to use a direct to task notification in place of a binary semaphore! https://www.FreeRTOS.org/RTOS-task-notifications.html This old vSemaphoreCreateBinary() macro is now deprecated in favour of the xSemaphoreCreateBinary() function. Note that binary semaphores created using the vSemaphoreCreateBinary() macro are created in a state such that the first call to 'take' the semaphore would pass, whereas binary semaphores created using xSemaphoreCreateBinary() are created in a state such that the the semaphore must first be 'given' before it can be 'taken'. Macro that implements a semaphore by using the existing queue mechanism. The queue length is 1 as this is a binary semaphore. The data size is 0 as we don't want to actually store any data - we just want to know if the queue is empty or full. This type of semaphore can be used for pure synchronisation between tasks or between an interrupt and a task. The semaphore need not be given back once obtained, so one task/interrupt can continuously 'give' the semaphore while another continuously 'takes' the semaphore. For this reason this type of semaphore does not use a priority inheritance mechanism. For an alternative that does use priority inheritance see xSemaphoreCreateMutex(). Example usage: SemaphoreHandle_t xSemaphore = NULL; void vATask( void * pvParameters ) { // Semaphore cannot be used before a call to vSemaphoreCreateBinary (). // This is a macro so pass the variable in directly.

vSemaphoreCreateBinary( xSemaphore ) ; if( xSemaphore != NULL ) { // The semaphore was created successfully. // The semaphore can now be used. } } - Parameters xSemaphore -- Handle to the created semaphore. Should be of type SemaphoreHandle_t. - - xSemaphoreCreateBinary() Creates a new binary semaphore instance, and returns a handle by which the new semaphore can be referenced. In many usage scenarios it is faster and more memory efficient to use a direct to task notification in place of a binary semaphore! https://www.FreeRTOS.org/RTOS-task-notifications.html Internally, within the FreeRTOS implementation, binary semaphores use a block of memory, in which the semaphore structure is stored. If a binary semaphore is created using xSemaphoreCreateBinary() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateBinary() function. (see https://www.FreeRTOS.org/a00111.html). If a binary semaphore is created using xSemaphoreCreateBinaryStatic() then the application writer must provide the memory. xSemaphoreCreateBinaryStatic() therefore allows a binary semaphore to be created without using any dynamic memory allocation. The old vSemaphoreCreateBinary() macro is now deprecated in favour of this xSemaphoreCreateBinary() function. Note that binary semaphores created using the vSemaphoreCreateBinary() macro are created in a state such that the first call to 'take' the semaphore would pass, whereas binary semaphores created using xSemaphoreCreateBinary() are created in a state such that the the semaphore must first be 'given' before it can be 'taken'. This type of semaphore can be used for pure synchronisation between tasks or between an interrupt and a task. The semaphore need not be given back once obtained, so one task/interrupt can continuously 'give' the semaphore while another continuously 'takes' the semaphore. For this reason this type of semaphore does not use a priority inheritance mechanism. For an alternative that does use priority inheritance see xSemaphoreCreateMutex(). Example usage: SemaphoreHandle_t xSemaphore = NULL; void vATask( void * pvParameters ) { // Semaphore cannot be used before a call to xSemaphoreCreateBinary(). // This is a macro so pass the variable in directly.

In many usage scenarios it is faster and more memory efficient to use a direct to task notification in place of a binary semaphore! https://www.FreeRTOS.org/RTOS-task-notifications.html Internally, within the FreeRTOS implementation, binary semaphores use a block of memory, in which the semaphore structure is stored. If a binary semaphore is created using xSemaphoreCreateBinary() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateBinary() function. (see https://www.FreeRTOS.org/a00111.html). If a binary semaphore is created using xSemaphoreCreateBinaryStatic() then the application writer must provide the memory. xSemaphoreCreateBinaryStatic() therefore allows a binary semaphore to be created without using any dynamic memory allocation. This type of semaphore can be used for pure synchronisation between tasks or between an interrupt and a task. The semaphore need not be given back once obtained, so one task/interrupt can continuously 'give' the semaphore while another continuously 'takes' the semaphore. For this reason this type of semaphore does not use a priority inheritance mechanism. For an alternative that does use priority inheritance see xSemaphoreCreateMutex(). Example usage: SemaphoreHandle_t xSemaphore = NULL; StaticSemaphore_t xSemaphoreBuffer; void vATask( void * pvParameters ) { // Semaphore cannot be used before a call to xSemaphoreCreateBinary(). // The semaphore's data structures will be placed in the xSemaphoreBuffer // variable, the address of which is passed into the function. The // function's parameter is not NULL, so the function will not attempt any // dynamic memory allocation, and therefore the function will not return // return NULL.

Rest of task code goes here. } - Parameters pxStaticSemaphore -- Must point to a variable of type StaticSemaphore_t, which will then be used to hold the semaphore's data structure, removing the need for the memory to be allocated dynamically. - - Returns If the semaphore is created then a handle to the created semaphore is returned. If pxSemaphoreBuffer is NULL then NULL is returned. - xSemaphoreTake(xSemaphore, xBlockTime) Macro to obtain a semaphore. The semaphore must have previously been created with a call to xSemaphoreCreateBinary(), xSemaphoreCreateMutex() or xSemaphoreCreateCounting(). Example usage: SemaphoreHandle_t xSemaphore = NULL; // A task that creates a semaphore.

The time in ticks to wait for the semaphore to become available. The macro portTICK_PERIOD_MS can be used to convert this to a real time. A block time of zero can be used to poll the semaphore. A block time of portMAX_DELAY can be used to block indefinitely (provided INCLUDE_vTaskSuspend is set to 1 in FreeRTOSConfig.h). - - Returns pdTRUE if the semaphore was obtained. pdFALSE if xBlockTime expired without the semaphore becoming available. - xSemaphoreTakeRecursive(xMutex, xBlockTime) Macro to recursively obtain, or 'take', a mutex type semaphore. The mutex must have previously been created using a call to xSemaphoreCreateRecursiveMutex(); configUSE_RECURSIVE_MUTEXES must be set to 1 in FreeRTOSConfig.h for this macro to be available. This macro must not be used on mutexes created using xSemaphoreCreateMutex(). A mutex used recursively can be 'taken' repeatedly by the owner. The mutex doesn't become available again until the owner has called xSemaphoreGiveRecursive() for each successful 'take' request. For example, if a task successfully 'takes' the same mutex 5 times then the mutex will not be available to any other task until it has also 'given' the mutex back exactly five times.

For some reason due to the nature of the code further calls to // xSemaphoreTakeRecursive() are made on the same mutex. In real // code these would not be just sequential calls as this would make // no sense. Instead the calls are likely to be buried inside // a more complex call structure. xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 ); xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 ); // The mutex has now been 'taken' three times, so will not be // available to another task until it has also been given back // three times. Again it is unlikely that real code would have // these calls sequentially, but instead buried in a more complex // call structure. This is just for illustrative purposes. xSemaphoreGiveRecursive( xMutex ); xSemaphoreGiveRecursive( xMutex ); xSemaphoreGiveRecursive( xMutex ); // Now the mutex can be taken by other tasks. } else { // We could not obtain the mutex and can therefore not access // the shared resource safely. } } } - Parameters xMutex -- A handle to the mutex being obtained. This is the handle returned by xSemaphoreCreateRecursiveMutex(); xBlockTime -- The time in ticks to wait for the semaphore to become available. The macro portTICK_PERIOD_MS can be used to convert this to a real time. A block time of zero can be used to poll the semaphore. If the task already owns the semaphore then xSemaphoreTakeRecursive() will return immediately no matter what the value of xBlockTime. - - Returns pdTRUE if the semaphore was obtained. pdFALSE if xBlockTime expired without the semaphore becoming available. - xSemaphoreGive(xSemaphore) Macro to release a semaphore. The semaphore must have previously been created with a call to xSemaphoreCreateBinary(), xSemaphoreCreateMutex() or xSemaphoreCreateCounting(). and obtained using sSemaphoreTake(). This macro must not be used from an ISR. See xSemaphoreGiveFromISR () for an alternative which can be used from an ISR. This macro must also not be used on semaphores created using xSemaphoreCreateRecursiveMutex(). Example usage: SemaphoreHandle_t xSemaphore = NULL; void vATask( void * pvParameters ) { // Create the semaphore to guard a shared resource. xSemaphore = vSemaphoreCreateBinary(); if( xSemaphore != NULL ) { if( xSemaphoreGive( xSemaphore ) != pdTRUE )

{ // We would not expect this call to fail because we must have // obtained the semaphore to get here. } } } } - Parameters xSemaphore -- A handle to the semaphore being released. This is the handle returned when the semaphore was created. - - Returns pdTRUE if the semaphore was released. pdFALSE if an error occurred. Semaphores are implemented using queues. An error can occur if there is no space on the queue to post a message - indicating that the semaphore was not first obtained correctly. - xSemaphoreGiveRecursive(xMutex) Macro to recursively release, or 'give', a mutex type semaphore. The mutex must have previously been created using a call to xSemaphoreCreateRecursiveMutex(); configUSE_RECURSIVE_MUTEXES must be set to 1 in FreeRTOSConfig.h for this macro to be available. This macro must not be used on mutexes created using xSemaphoreCreateMutex(). A mutex used recursively can be 'taken' repeatedly by the owner. The mutex doesn't become available again until the owner has called xSemaphoreGiveRecursive() for each successful 'take' request. For example, if a task successfully 'takes' the same mutex 5 times then the mutex will not be available to any other task until it has also 'given' the mutex back exactly five times.

For some reason due to the nature of the code further calls to // xSemaphoreTakeRecursive() are made on the same mutex. In real // code these would not be just sequential calls as this would make // no sense. Instead the calls are likely to be buried inside // a more complex call structure. xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 ); xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 ); // The mutex has now been 'taken' three times, so will not be // available to another task until it has also been given back // three times. Again it is unlikely that real code would have // these calls sequentially, it would be more likely that the calls // to xSemaphoreGiveRecursive() would be called as a call stack // unwound. This is just for demonstrative purposes. xSemaphoreGiveRecursive( xMutex ); xSemaphoreGiveRecursive( xMutex ); xSemaphoreGiveRecursive( xMutex ); // Now the mutex can be taken by other tasks. } else { // We could not obtain the mutex and can therefore not access // the shared resource safely. } } } - Parameters xMutex -- A handle to the mutex being released, or 'given'. This is the handle returned by xSemaphoreCreateMutex(); - - Returns pdTRUE if the semaphore was given. - xSemaphoreGiveFromISR(xSemaphore, pxHigherPriorityTaskWoken) Macro to release a semaphore. The semaphore must have previously been created with a call to xSemaphoreCreateBinary() or xSemaphoreCreateCounting(). Mutex type semaphores (those created using a call to xSemaphoreCreateMutex()) must not be used with this macro. This macro can be used from an ISR.

A handle to the semaphore being released. This is the handle returned when the semaphore was created. pxHigherPriorityTaskWoken -- xSemaphoreGiveFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if giving the semaphore caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If xSemaphoreGiveFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited. - - Returns pdTRUE if the semaphore was successfully given, otherwise errQUEUE_FULL. - xSemaphoreTakeFromISR(xSemaphore, pxHigherPriorityTaskWoken) Macro to take a semaphore from an ISR. The semaphore must have previously been created with a call to xSemaphoreCreateBinary() or xSemaphoreCreateCounting(). Mutex type semaphores (those created using a call to xSemaphoreCreateMutex()) must not be used with this macro. This macro can be used from an ISR, however taking a semaphore from an ISR is not a common operation. It is likely to only be useful when taking a counting semaphore when an interrupt is obtaining an object from a resource pool (when the semaphore count indicates the number of resources available). - Parameters xSemaphore -- A handle to the semaphore being taken. This is the handle returned when the semaphore was created. pxHigherPriorityTaskWoken -- xSemaphoreTakeFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if taking the semaphore caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If xSemaphoreTakeFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited. - - Returns pdTRUE if the semaphore was successfully taken, otherwise pdFALSE - xSemaphoreCreateMutex() Creates a new mutex type semaphore instance, and returns a handle by which the new mutex can be referenced. Internally, within the FreeRTOS implementation, mutex semaphores use a block of memory, in which the mutex structure is stored. If a mutex is created using xSemaphoreCreateMutex() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateMutex() function. (see https://www.FreeRTOS.org/a00111.html). If a mutex is created using xSemaphoreCreateMutexStatic() then the application writer must provided the memory. xSemaphoreCreateMutexStatic() therefore allows a mutex to be created without using any dynamic memory allocation. Mutexes created using this function can be accessed using the xSemaphoreTake() and xSemaphoreGive() macros. The xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros must not be used.

This type of semaphore uses a priority inheritance mechanism so a task 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the semaphore it is no longer required. Mutex type semaphores cannot be used from within interrupt service routines. See xSemaphoreCreateBinary() for an alternative implementation that can be used for pure synchronisation (where one task or interrupt always 'gives' the semaphore and another always 'takes' the semaphore) and from within interrupt service routines. Example usage: SemaphoreHandle_t xSemaphore; void vATask( void * pvParameters ) { // Semaphore cannot be used before a call to xSemaphoreCreateMutex(). // This is a macro so pass the variable in directly.

The semaphore can now be used. } } - Returns If the mutex was successfully created then a handle to the created semaphore is returned. If there was not enough heap to allocate the mutex data structures then NULL is returned. - xSemaphoreCreateMutexStatic(pxMutexBuffer) Creates a new mutex type semaphore instance, and returns a handle by which the new mutex can be referenced. Internally, within the FreeRTOS implementation, mutex semaphores use a block of memory, in which the mutex structure is stored. If a mutex is created using xSemaphoreCreateMutex() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateMutex() function. (see https://www.FreeRTOS.org/a00111.html). If a mutex is created using xSemaphoreCreateMutexStatic() then the application writer must provided the memory. xSemaphoreCreateMutexStatic() therefore allows a mutex to be created without using any dynamic memory allocation. Mutexes created using this function can be accessed using the xSemaphoreTake() and xSemaphoreGive() macros. The xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros must not be used.

This type of semaphore uses a priority inheritance mechanism so a task 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the semaphore it is no longer required. Mutex type semaphores cannot be used from within interrupt service routines. See xSemaphoreCreateBinary() for an alternative implementation that can be used for pure synchronisation (where one task or interrupt always 'gives' the semaphore and another always 'takes' the semaphore) and from within interrupt service routines. Example usage: SemaphoreHandle_t xSemaphore; StaticSemaphore_t xMutexBuffer; void vATask( void * pvParameters ) { // A mutex cannot be used before it has been created. xMutexBuffer is // into xSemaphoreCreateMutexStatic() so no dynamic memory allocation is // attempted.

As no dynamic memory allocation was performed, xSemaphore cannot be NULL, // so there is no need to check it. } - Parameters pxMutexBuffer -- Must point to a variable of type StaticSemaphore_t, which will be used to hold the mutex's data structure, removing the need for the memory to be allocated dynamically. - - Returns If the mutex was successfully created then a handle to the created mutex is returned. If pxMutexBuffer was NULL then NULL is returned. - xSemaphoreCreateRecursiveMutex() Creates a new recursive mutex type semaphore instance, and returns a handle by which the new recursive mutex can be referenced. Internally, within the FreeRTOS implementation, recursive mutexes use a block of memory, in which the mutex structure is stored. If a recursive mutex is created using xSemaphoreCreateRecursiveMutex() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateRecursiveMutex() function. (see https://www.FreeRTOS.org/a00111.html).

If a recursive mutex is created using xSemaphoreCreateRecursiveMutexStatic() then the application writer must provide the memory that will get used by the mutex. xSemaphoreCreateRecursiveMutexStatic () therefore allows a recursive mutex to be created without using any dynamic memory allocation. Mutexes created using this macro can be accessed using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros. The xSemaphoreTake() and xSemaphoreGive() macros must not be used. A mutex used recursively can be 'taken' repeatedly by the owner. The mutex doesn't become available again until the owner has called xSemaphoreGiveRecursive() for each successful 'take' request. For example, if a task successfully 'takes' the same mutex 5 times then the mutex will not be available to any other task until it has also 'given' the mutex back exactly five times. This type of semaphore uses a priority inheritance mechanism so a task 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the semaphore it is no longer required. Mutex type semaphores cannot be used from within interrupt service routines. See xSemaphoreCreateBinary() for an alternative implementation that can be used for pure synchronisation (where one task or interrupt always 'gives' the semaphore and another always 'takes' the semaphore) and from within interrupt service routines. Example usage: SemaphoreHandle_t xSemaphore; void vATask( void * pvParameters ) { // Semaphore cannot be used before a call to xSemaphoreCreateMutex(). // This is a macro so pass the variable in directly.

{ // The semaphore was created successfully. // The semaphore can now be used. } } - Returns xSemaphore Handle to the created mutex semaphore. Should be of type SemaphoreHandle_t. - xSemaphoreCreateRecursiveMutexStatic(pxStaticSemaphore) Creates a new recursive mutex type semaphore instance, and returns a handle by which the new recursive mutex can be referenced. Internally, within the FreeRTOS implementation, recursive mutexes use a block of memory, in which the mutex structure is stored. If a recursive mutex is created using xSemaphoreCreateRecursiveMutex() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateRecursiveMutex() function. (see https://www.FreeRTOS.org/a00111.html).

If a recursive mutex is created using xSemaphoreCreateRecursiveMutexStatic() then the application writer must provide the memory that will get used by the mutex. xSemaphoreCreateRecursiveMutexStatic () therefore allows a recursive mutex to be created without using any dynamic memory allocation. Mutexes created using this macro can be accessed using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros. The xSemaphoreTake() and xSemaphoreGive() macros must not be used. A mutex used recursively can be 'taken' repeatedly by the owner. The mutex doesn't become available again until the owner has called xSemaphoreGiveRecursive() for each successful 'take' request. For example, if a task successfully 'takes' the same mutex 5 times then the mutex will not be available to any other task until it has also 'given' the mutex back exactly five times. This type of semaphore uses a priority inheritance mechanism so a task 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the semaphore it is no longer required. Mutex type semaphores cannot be used from within interrupt service routines. See xSemaphoreCreateBinary() for an alternative implementation that can be used for pure synchronisation (where one task or interrupt always 'gives' the semaphore and another always 'takes' the semaphore) and from within interrupt service routines. Example usage: SemaphoreHandle_t xSemaphore; StaticSemaphore_t xMutexBuffer; void vATask( void * pvParameters ) { // A recursive semaphore cannot be used before it is created. Here a // recursive mutex is created using xSemaphoreCreateRecursiveMutexStatic(). // The address of xMutexBuffer is passed into the function, and will hold // the mutexes data structures - so no dynamic memory allocation will be // attempted.

As no dynamic memory allocation was performed, xSemaphore cannot be NULL, // so there is no need to check it. } - Parameters pxStaticSemaphore -- Must point to a variable of type StaticSemaphore_t, which will then be used to hold the recursive mutex's data structure, removing the need for the memory to be allocated dynamically. - - Returns If the recursive mutex was successfully created then a handle to the created recursive mutex is returned. If pxStaticSemaphore was NULL then NULL is returned. - xSemaphoreCreateCounting(uxMaxCount, uxInitialCount) Creates a new counting semaphore instance, and returns a handle by which the new counting semaphore can be referenced. In many usage scenarios it is faster and more memory efficient to use a direct to task notification in place of a counting semaphore! https://www.FreeRTOS.org/RTOS-task-notifications.html Internally, within the FreeRTOS implementation, counting semaphores use a block of memory, in which the counting semaphore structure is stored. If a counting semaphore is created using xSemaphoreCreateCounting() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateCounting() function. (see https://www.FreeRTOS.org/a00111.html).

If a counting semaphore is created using xSemaphoreCreateCountingStatic() then the application writer can instead optionally provide the memory that will get used by the counting semaphore. xSemaphoreCreateCountingStatic() therefore allows a counting semaphore to be created without using any dynamic memory allocation. Counting semaphores are typically used for two things: 1) Counting events. In this usage scenario an event handler will 'give' a semaphore each time an event occurs (incrementing the semaphore count value), and a handler task will 'take' a semaphore each time it processes an event (decrementing the semaphore count value). The count value is therefore the difference between the number of events that have occurred and the number that have been processed. In this case it is desirable for the initial count value to be zero.

2) Resource management. In this usage scenario the count value indicates the number of resources available. To obtain control of a resource a task must first obtain a semaphore - decrementing the semaphore count value. When the count value reaches zero there are no free resources. When a task finishes with the resource it 'gives' the semaphore back - incrementing the semaphore count value. In this case it is desirable for the initial count value to be equal to the maximum count value, indicating that all resources are free. Example usage: SemaphoreHandle_t xSemaphore; void vATask( void * pvParameters ) { SemaphoreHandle_t xSemaphore = NULL; // Semaphore cannot be used before a call to xSemaphoreCreateCounting(). // The max value to which the semaphore can count should be 10, and the // initial value assigned to the count should be 0.

{ // The semaphore was created successfully. // The semaphore can now be used. } } - Parameters uxMaxCount -- The maximum count value that can be reached. When the semaphore reaches this value it can no longer be 'given'. uxInitialCount -- The count value assigned to the semaphore when it is created. - - Returns Handle to the created semaphore. Null if the semaphore could not be created. - xSemaphoreCreateCountingStatic(uxMaxCount, uxInitialCount, pxSemaphoreBuffer) Creates a new counting semaphore instance, and returns a handle by which the new counting semaphore can be referenced. In many usage scenarios it is faster and more memory efficient to use a direct to task notification in place of a counting semaphore! https://www.FreeRTOS.org/RTOS-task-notifications.html Internally, within the FreeRTOS implementation, counting semaphores use a block of memory, in which the counting semaphore structure is stored. If a counting semaphore is created using xSemaphoreCreateCounting() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateCounting() function. (see https://www.FreeRTOS.org/a00111.html). If a counting semaphore is created using xSemaphoreCreateCountingStatic() then the application writer must provide the memory. xSemaphoreCreateCountingStatic() therefore allows a counting semaphore to be created without using any dynamic memory allocation. Counting semaphores are typically used for two things: 1) Counting events. In this usage scenario an event handler will 'give' a semaphore each time an event occurs (incrementing the semaphore count value), and a handler task will 'take' a semaphore each time it processes an event (decrementing the semaphore count value). The count value is therefore the difference between the number of events that have occurred and the number that have been processed. In this case it is desirable for the initial count value to be zero.

The max // value to which the semaphore can count is 10, and the initial value // assigned to the count will be 0. The address of xSemaphoreBuffer is // passed in and will be used to hold the semaphore structure, so no dynamic // memory allocation will be used. xSemaphore = xSemaphoreCreateCounting( 10, 0, &xSemaphoreBuffer ); // No memory allocation was attempted so xSemaphore cannot be NULL, so there // is no need to check its value. } - Parameters uxMaxCount -- The maximum count value that can be reached. When the semaphore reaches this value it can no longer be 'given'. uxInitialCount -- The count value assigned to the semaphore when it is created. pxSemaphoreBuffer -- Must point to a variable of type StaticSemaphore_t, which will then be used to hold the semaphore's data structure, removing the need for the memory to be allocated dynamically. - - Returns If the counting semaphore was successfully created then a handle to the created counting semaphore is returned. If pxSemaphoreBuffer was NULL then NULL is returned. - vSemaphoreDelete(xSemaphore)

This function must be used with care. For example, do not delete a mutex type semaphore if the mutex is held by a task. - Parameters xSemaphore -- A handle to the semaphore to be deleted. - - xSemaphoreGetMutexHolder(xSemaphore) If xMutex is indeed a mutex type semaphore, return the current mutex holder. If xMutex is not a mutex type semaphore, or the mutex is available (not held by a task), return NULL. Note: This is a good way of determining if the calling task is the mutex holder, but not a good way of determining the identity of the mutex holder as the holder may change between the function exiting and the returned value being tested. - xSemaphoreGetMutexHolderFromISR(xSemaphore) If xMutex is indeed a mutex type semaphore, return the current mutex holder. If xMutex is not a mutex type semaphore, or the mutex is available (not held by a task), return NULL. - uxSemaphoreGetCount(xSemaphore) If the semaphore is a counting semaphore then uxSemaphoreGetCount() returns its current count value. If the semaphore is a binary semaphore then uxSemaphoreGetCount() returns 1 if the semaphore is available, and 0 if the semaphore is not available. - uxSemaphoreGetCountFromISR(xSemaphore) semphr.h UBaseType_t uxSemaphoreGetCountFromISR( SemaphoreHandle_t xSemaphore ); If the semaphore is a counting semaphore then uxSemaphoreGetCountFromISR() returns its current count value. If the semaphore is a binary semaphore then uxSemaphoreGetCountFromISR() returns 1 if the semaphore is available, and 0 if the semaphore is not available. - xSemaphoreGetStaticBuffer(xSemaphore, ppxSemaphoreBuffer) Retrieve pointer to a statically created binary semaphore, counting semaphore, or mutex semaphore's data structure buffer. This is the same buffer that is supplied at the time of creation. - Parameters xSemaphore -- The semaphore for which to retrieve the buffer. ppxSemaphoreBuffer -- Used to return a pointer to the semaphore's data structure buffer. - - Returns pdTRUE if buffer was retrieved, pdFALSE otherwise.

Type Definitions - typedef QueueHandle_t SemaphoreHandle_t Timer API Header File components/freertos/FreeRTOS-Kernel/include/freertos/timers.h This header file can be included with: #include "freertos/timers.h" Functions - TimerHandle_t xTimerCreate(const char *const pcTimerName, const TickType_t xTimerPeriodInTicks, const BaseType_t xAutoReload, void *const pvTimerID, TimerCallbackFunction_t pxCallbackFunction) Creates a new software timer instance, and returns a handle by which the created software timer can be referenced. Internally, within the FreeRTOS implementation, software timers use a block of memory, in which the timer data structure is stored. If a software timer is created using xTimerCreate() then the required memory is automatically dynamically allocated inside the xTimerCreate() function. (see https://www.FreeRTOS.org/a00111.html).

If a software timer is created using xTimerCreateStatic() then the application writer must provide the memory that will get used by the software timer. xTimerCreateStatic() therefore allows a software timer to be created without using any dynamic memory allocation. Timers are created in the dormant state. The xTimerStart(), xTimerReset(), xTimerStartFromISR(), xTimerResetFromISR(), xTimerChangePeriod() and xTimerChangePeriodFromISR() API functions can all be used to transition a timer into the active state.

A text name that is assigned to the timer. This is done purely to assist debugging. The kernel itself only ever references a timer by its handle, and never by its name. xTimerPeriodInTicks -- The timer period. The time is defined in tick periods so the constant portTICK_PERIOD_MS can be used to convert a time that has been specified in milliseconds. For example, if the timer must expire after 100 ticks, then xTimerPeriodInTicks should be set to 100. Alternatively, if the timer must expire after 500ms, then xPeriod can be set to ( 500 / portTICK_PERIOD_MS ) provided configTICK_RATE_HZ is less than or equal to 1000. Time timer period must be greater than 0. xAutoReload -- If xAutoReload is set to pdTRUE then the timer will expire repeatedly with a frequency set by the xTimerPeriodInTicks parameter. If xAutoReload is set to pdFALSE then the timer will be a one-shot timer and enter the dormant state after it expires.

An identifier that is assigned to the timer being created. Typically this would be used in the timer callback function to identify which timer expired when the same callback function is assigned to more than one timer. pxCallbackFunction -- The function to call when the timer expires. Callback functions must have the prototype defined by TimerCallbackFunction_t, which is "void vCallbackFunction( TimerHandle_t xTimer );". - - Returns If the timer is successfully created then a handle to the newly created timer is returned. If the timer cannot be created because there is insufficient FreeRTOS heap remaining to allocate the timer structures then NULL is returned. - TimerHandle_t xTimerCreateStatic(const char *const pcTimerName, const TickType_t xTimerPeriodInTicks, const BaseType_t xAutoReload, void *const pvTimerID, TimerCallbackFunction_t pxCallbackFunction, StaticTimer_t *pxTimerBuffer) Creates a new software timer instance, and returns a handle by which the created software timer can be referenced. Internally, within the FreeRTOS implementation, software timers use a block of memory, in which the timer data structure is stored. If a software timer is created using xTimerCreate() then the required memory is automatically dynamically allocated inside the xTimerCreate() function. (see https://www.FreeRTOS.org/a00111.html).

If a software timer is created using xTimerCreateStatic() then the application writer must provide the memory that will get used by the software timer. xTimerCreateStatic() therefore allows a software timer to be created without using any dynamic memory allocation. Timers are created in the dormant state. The xTimerStart(), xTimerReset(), xTimerStartFromISR(), xTimerResetFromISR(), xTimerChangePeriod() and xTimerChangePeriodFromISR() API functions can all be used to transition a timer into the active state.

A text name that is assigned to the timer. This is done purely to assist debugging. The kernel itself only ever references a timer by its handle, and never by its name. xTimerPeriodInTicks -- The timer period. The time is defined in tick periods so the constant portTICK_PERIOD_MS can be used to convert a time that has been specified in milliseconds. For example, if the timer must expire after 100 ticks, then xTimerPeriodInTicks should be set to 100. Alternatively, if the timer must expire after 500ms, then xPeriod can be set to ( 500 / portTICK_PERIOD_MS ) provided configTICK_RATE_HZ is less than or equal to 1000. The timer period must be greater than 0. xAutoReload -- If xAutoReload is set to pdTRUE then the timer will expire repeatedly with a frequency set by the xTimerPeriodInTicks parameter. If xAutoReload is set to pdFALSE then the timer will be a one-shot timer and enter the dormant state after it expires.

An identifier that is assigned to the timer being created. Typically this would be used in the timer callback function to identify which timer expired when the same callback function is assigned to more than one timer. pxCallbackFunction -- The function to call when the timer expires. Callback functions must have the prototype defined by TimerCallbackFunction_t, which is "void vCallbackFunction( TimerHandle_t xTimer );". pxTimerBuffer -- Must point to a variable of type StaticTimer_t, which will be then be used to hold the software timer's data structures, removing the need for the memory to be allocated dynamically. - - Returns If the timer is created then a handle to the created timer is returned. If pxTimerBuffer was NULL then NULL is returned. - void *pvTimerGetTimerID(const TimerHandle_t xTimer) Returns the ID assigned to the timer. IDs are assigned to timers using the pvTimerID parameter of the call to xTimerCreated() that was used to create the timer, and by calling the vTimerSetTimerID() API function. If the same callback function is assigned to multiple timers then the timer ID can be used as time specific (timer local) storage. Example usage: See the xTimerCreate() API function example usage scenario. - Parameters xTimer -- The timer being queried. - Returns The ID assigned to the timer being queried. - void vTimerSetTimerID(TimerHandle_t

Sets the ID assigned to the timer. IDs are assigned to timers using the pvTimerID parameter of the call to xTimerCreated() that was used to create the timer. If the same callback function is assigned to multiple timers then the timer ID can be used as time specific (timer local) storage. Example usage: See the xTimerCreate() API function example usage scenario. - Parameters xTimer -- The timer being updated. pvNewID -- The ID to assign to the timer. - - BaseType_t xTimerIsTimerActive(TimerHandle_t xTimer) Queries a timer to see if it is active or dormant. A timer will be dormant if: 1) It has been created but not started, or 2) It is an expired one-shot timer that has not been restarted. Timers are created in the dormant state. The xTimerStart(), xTimerReset(), xTimerStartFromISR(), xTimerResetFromISR(), xTimerChangePeriod() and xTimerChangePeriodFromISR() API functions can all be used to transition a timer into the active state.

The timer being queried. - Returns pdFALSE will be returned if the timer is dormant. A value other than pdFALSE will be returned if the timer is active. - TaskHandle_t xTimerGetTimerDaemonTaskHandle(void) Simply returns the handle of the timer service/daemon task. It it not valid to call xTimerGetTimerDaemonTaskHandle() before the scheduler has been started. - BaseType_t xTimerPendFunctionCallFromISR(PendedFunction_t xFunctionToPend, void *pvParameter1, uint32_t ulParameter2, BaseType_t *pxHigherPriorityTaskWoken) Used from application interrupt service routines to defer the execution of a function to the RTOS daemon task (the timer service task, hence this function is implemented in timers.c and is prefixed with 'Timer'). Ideally an interrupt service routine (ISR) is kept as short as possible, but sometimes an ISR either has a lot of processing to do, or needs to perform processing that is not deterministic. In these cases xTimerPendFunctionCallFromISR() can be used to defer processing of a function to the RTOS daemon task. A mechanism is provided that allows the interrupt to return directly to the task that will subsequently execute the pended callback function. This allows the callback function to execute contiguously in time with the interrupt - just as if the callback had executed in the interrupt itself.

The value of the callback function's second parameter. 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 (which is set using configTIMER_TASK_PRIORITY in FreeRTOSConfig.h) is higher than the priority of the currently running task (the task the interrupt interrupted) then *pxHigherPriorityTaskWoken will be set to pdTRUE within xTimerPendFunctionCallFromISR(), 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. - - Returns pdPASS is returned if the message was successfully sent to the timer daemon task, otherwise pdFALSE is returned. - BaseType_t xTimerPendFunctionCall(PendedFunction_t xFunctionToPend, void *pvParameter1, uint32_t ulParameter2, TickType_t xTicksToWait) Used to defer the execution of a function to the RTOS daemon task (the timer service task, hence this function is implemented in timers.c and is prefixed with 'Timer'). - Parameters xFunctionToPend --

Calling this function will result in a message being sent to the timer daemon task on a queue. xTicksToWait is the amount of time the calling task should remain in the Blocked state (so not using any processing time) for space to become available on the timer queue if the queue is found to be full. - - Returns pdPASS is returned if the message was successfully sent to the timer daemon task, otherwise pdFALSE is returned. - const char *pcTimerGetName(TimerHandle_t xTimer) Returns the name that was assigned to a timer when the timer was created. - Parameters xTimer -- The handle of the timer being queried. - Returns The name assigned to the timer specified by the xTimer parameter. - void vTimerSetReloadMode(TimerHandle_t xTimer, const BaseType_t xAutoReload) Updates a timer to be either an auto-reload timer, in which case the timer automatically resets itself each time it expires, or a one-shot timer, in which case the timer will only expire once unless it is manually restarted. - Parameters xTimer -- The handle of the timer being updated.

Specifies the time, in ticks, that the calling task should be held in the Blocked state to wait for the start command to be successfully sent to the timer command queue, should the queue already be full when xTimerStart() was called. xTicksToWait is ignored if xTimerStart() is called before the scheduler is started. - - Returns pdFAIL will be returned if the start command could not be sent to the timer command queue even after xTicksToWait ticks had passed. pdPASS will be returned if the command was successfully sent to the timer command queue. When the command is actually processed will depend on the priority of the timer service/daemon task relative to other tasks in the system, although the timers expiry time is relative to when xTimerStart() is actually called. The timer service/daemon task priority is set by the configTIMER_TASK_PRIORITY configuration constant. - xTimerStop(xTimer, xTicksToWait) Timer functionality is provided by a timer service/daemon task. Many of the public FreeRTOS timer API functions send commands to the timer service task through a queue called the timer command queue. The timer command queue is private to the kernel itself and is not directly accessible to application code. The length of the timer command queue is set by the configTIMER_QUEUE_LENGTH configuration constant. xTimerStop() stops a timer that was previously started using either of the The xTimerStart(), xTimerReset(), xTimerStartFromISR(), xTimerResetFromISR(), xTimerChangePeriod() or xTimerChangePeriodFromISR() API functions. Stopping a timer ensures the timer is not in the active state. The configUSE_TIMERS configuration constant must be set to 1 for xTimerStop() to be available. Example usage: See the xTimerCreate() API function example usage scenario. - Parameters xTimer -- The handle of the timer being stopped. xTicksToWait --

Specifies the time, in ticks, that the calling task should be held in the Blocked state to wait for the stop command to be successfully sent to the timer command queue, should the queue already be full when xTimerStop() was called. xTicksToWait is ignored if xTimerStop() is called before the scheduler is started. - - Returns pdFAIL will be returned if the stop command could not be sent to the timer command queue even after xTicksToWait ticks had passed. pdPASS will be returned if the command was successfully sent to the timer command queue. When the command is actually processed will depend on the priority of the timer service/daemon task relative to other tasks in the system. The timer service/daemon task priority is set by the configTIMER_TASK_PRIORITY configuration constant. - xTimerChangePeriod(xTimer, xNewPeriod, xTicksToWait) Timer functionality is provided by a timer service/daemon task. Many of the public FreeRTOS timer API functions send commands to the timer service task through a queue called the timer command queue. The timer command queue is private to the kernel itself and is not directly accessible to application code. The length of the timer command queue is set by the configTIMER_QUEUE_LENGTH configuration constant. xTimerChangePeriod() changes the period of a timer that was previously created using the xTimerCreate() API function. xTimerChangePeriod() can be called to change the period of an active or dormant state timer. The configUSE_TIMERS configuration constant must be set to 1 for xTimerChangePeriod() to be available.

Specifies the time, in ticks, that the calling task should be held in the Blocked state to wait for the change period command to be successfully sent to the timer command queue, should the queue already be full when xTimerChangePeriod() was called. xTicksToWait is ignored if xTimerChangePeriod() is called before the scheduler is started. - - Returns pdFAIL will be returned if the change period command could not be sent to the timer command queue even after xTicksToWait ticks had passed. pdPASS will be returned if the command was successfully sent to the timer command queue. When the command is actually processed will depend on the priority of the timer service/daemon task relative to other tasks in the system. The timer service/daemon task priority is set by the configTIMER_TASK_PRIORITY configuration constant. - xTimerDelete(xTimer, xTicksToWait) Timer functionality is provided by a timer service/daemon task. Many of the public FreeRTOS timer API functions send commands to the timer service task through a queue called the timer command queue. The timer command queue is private to the kernel itself and is not directly accessible to application code. The length of the timer command queue is set by the configTIMER_QUEUE_LENGTH configuration constant. xTimerDelete() deletes a timer that was previously created using the xTimerCreate() API function. The configUSE_TIMERS configuration constant must be set to 1 for xTimerDelete() to be available. Example usage: See the xTimerChangePeriod() API function example usage scenario. - Parameters xTimer -- The handle of the timer being deleted. xTicksToWait --

Specifies the time, in ticks, that the calling task should be held in the Blocked state to wait for the delete command to be successfully sent to the timer command queue, should the queue already be full when xTimerDelete() was called. xTicksToWait is ignored if xTimerDelete() is called before the scheduler is started. - - Returns pdFAIL will be returned if the delete command could not be sent to the timer command queue even after xTicksToWait ticks had passed. pdPASS will be returned if the command was successfully sent to the timer command queue. When the command is actually processed will depend on the priority of the timer service/daemon task relative to other tasks in the system. The timer service/daemon task priority is set by the configTIMER_TASK_PRIORITY configuration constant. - xTimerReset(xTimer, xTicksToWait) Timer functionality is provided by a timer service/daemon task. Many of the public FreeRTOS timer API functions send commands to the timer service task through a queue called the timer command queue. The timer command queue is private to the kernel itself and is not directly accessible to application code. The length of the timer command queue is set by the configTIMER_QUEUE_LENGTH configuration constant. xTimerReset() re-starts a timer that was previously created using the xTimerCreate() API function. If the timer had already been started and was already in the active state, then xTimerReset() will cause the timer to re-evaluate its expiry time so that it is relative to when xTimerReset() was called. If the timer was in the dormant state then xTimerReset() has equivalent functionality to the xTimerStart() API function. Resetting a timer ensures the timer is in the active state. If the timer is not stopped, deleted, or reset in the mean time, the callback function associated with the timer will get called 'n' ticks after xTimerReset() was called, where 'n' is the timers defined period. It is valid to call xTimerReset() before the scheduler has been started, but when this is done the timer will not actually start until the scheduler is started, and the timers expiry time will be relative to when the scheduler is started, not relative to when xTimerReset() was called. The configUSE_TIMERS configuration constant must be set to 1 for xTimerReset() to be available.

Specifies the time, in ticks, that the calling task should be held in the Blocked state to wait for the reset command to be successfully sent to the timer command queue, should the queue already be full when xTimerReset() was called. xTicksToWait is ignored if xTimerReset() is called before the scheduler is started. - - Returns pdFAIL will be returned if the reset command could not be sent to the timer command queue even after xTicksToWait ticks had passed. pdPASS will be returned if the command was successfully sent to the timer command queue. When the command is actually processed will depend on the priority of the timer service/daemon task relative to other tasks in the system, although the timers expiry time is relative to when xTimerStart() is actually called. The timer service/daemon task priority is set by the configTIMER_TASK_PRIORITY configuration constant. - xTimerStartFromISR(xTimer, pxHigherPriorityTaskWoken) A version of xTimerStart() that can be called from an interrupt service routine.

The timer service/daemon task spends most of its time in the Blocked state, waiting for messages to arrive on the timer command queue. Calling xTimerStartFromISR() writes a message to the timer command queue, so has the potential to transition the timer service/daemon task out of the Blocked state. If calling xTimerStartFromISR() causes the timer service/daemon task to leave the Blocked state, and the timer service/ daemon task has a priority equal to or greater than the currently executing task (the task that was interrupted), then *pxHigherPriorityTaskWoken will get set to pdTRUE internally within the xTimerStartFromISR() function. If xTimerStartFromISR() sets this value to pdTRUE then a context switch should be performed before the interrupt exits. - - Returns pdFAIL will be returned if the start command could not be sent to the timer command queue. pdPASS will be returned if the command was successfully sent to the timer command queue. When the command is actually processed will depend on the priority of the timer service/daemon task relative to other tasks in the system, although the timers expiry time is relative to when xTimerStartFromISR() is actually called. The timer service/daemon task priority is set by the configTIMER_TASK_PRIORITY configuration constant. - xTimerStopFromISR(xTimer, pxHigherPriorityTaskWoken) A version of xTimerStop() that can be called from an interrupt service routine.

The timer service/daemon task spends most of its time in the Blocked state, waiting for messages to arrive on the timer command queue. Calling xTimerStopFromISR() writes a message to the timer command queue, so has the potential to transition the timer service/daemon task out of the Blocked state. If calling xTimerStopFromISR() causes the timer service/daemon task to leave the Blocked state, and the timer service/ daemon task has a priority equal to or greater than the currently executing task (the task that was interrupted), then *pxHigherPriorityTaskWoken will get set to pdTRUE internally within the xTimerStopFromISR() function. If xTimerStopFromISR() sets this value to pdTRUE then a context switch should be performed before the interrupt exits. - - Returns pdFAIL will be returned if the stop command could not be sent to the timer command queue. pdPASS will be returned if the command was successfully sent to the timer command queue. When the command is actually processed will depend on the priority of the timer service/daemon task relative to other tasks in the system. The timer service/daemon task priority is set by the configTIMER_TASK_PRIORITY configuration constant. - xTimerChangePeriodFromISR(xTimer, xNewPeriod, pxHigherPriorityTaskWoken) A version of xTimerChangePeriod() that can be called from an interrupt service routine.

The timer service/daemon task spends most of its time in the Blocked state, waiting for messages to arrive on the timer command queue. Calling xTimerChangePeriodFromISR() writes a message to the timer command queue, so has the potential to transition the timer service/ daemon task out of the Blocked state. If calling xTimerChangePeriodFromISR() causes the timer service/daemon task to leave the Blocked state, and the timer service/daemon task has a priority equal to or greater than the currently executing task (the task that was interrupted), then *pxHigherPriorityTaskWoken will get set to pdTRUE internally within the xTimerChangePeriodFromISR() function. If xTimerChangePeriodFromISR() sets this value to pdTRUE then a context switch should be performed before the interrupt exits. - - Returns pdFAIL will be returned if the command to change the timers period could not be sent to the timer command queue. pdPASS will be returned if the command was successfully sent to the timer command queue. When the command is actually processed will depend on the priority of the timer service/daemon task relative to other tasks in the system. The timer service/daemon task priority is set by the configTIMER_TASK_PRIORITY configuration constant. - xTimerResetFromISR(xTimer, pxHigherPriorityTaskWoken) A version of xTimerReset() that can be called from an interrupt service routine.

The timer service/daemon task spends most of its time in the Blocked state, waiting for messages to arrive on the timer command queue. Calling xTimerResetFromISR() writes a message to the timer command queue, so has the potential to transition the timer service/daemon task out of the Blocked state. If calling xTimerResetFromISR() causes the timer service/daemon task to leave the Blocked state, and the timer service/ daemon task has a priority equal to or greater than the currently executing task (the task that was interrupted), then *pxHigherPriorityTaskWoken will get set to pdTRUE internally within the xTimerResetFromISR() function. If xTimerResetFromISR() sets this value to pdTRUE then a context switch should be performed before the interrupt exits. - - Returns pdFAIL will be returned if the reset command could not be sent to the timer command queue. pdPASS will be returned if the command was successfully sent to the timer command queue. When the command is actually processed will depend on the priority of the timer service/daemon task relative to other tasks in the system, although the timers expiry time is relative to when xTimerResetFromISR() is actually called. The timer service/daemon task priority is set by the configTIMER_TASK_PRIORITY configuration constant. Type Definitions - typedef struct tmrTimerControl *TimerHandle_t - typedef void (*TimerCallbackFunction_t)(TimerHandle_t xTimer) Defines the prototype to which timer callback functions must conform. - typedef void (*PendedFunction_t)(void*, uint32_t) Defines the prototype to which functions used with the xTimerPendFunctionCallFromISR() function must conform. Event Group API Header File components/freertos/FreeRTOS-Kernel/include/freertos/event_groups.h This header file can be included with: #include "freertos/event_groups.h" Functions - EventGroupHandle_t xEventGroupCreate(void)

If an event group is created using xEventGroupCreateStatic() 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. Example usage: // 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. } - Returns 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 https://www.FreeRTOS.org/a00111.html - EventGroupHandle_t xEventGroupCreateStatic(StaticEventGroup_t *pxEventGroupBuffer) 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 xEventGroupCreate() then the required memory is automatically dynamically allocated inside the xEventGroupCreate() function. (see https://www.FreeRTOS.org/a00111.html).

If an event group is created using xEventGroupCreateStatic() 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. Example usage: // 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.

xEventGroupCreateStatic( &xEventGroupBuffer ); - Parameters 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. - Returns If the event group was created then a handle to the event group is returned. If pxEventGroupBuffer was NULL then NULL is returned. - EventBits_t xEventGroupWaitBits(EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToWaitFor, const BaseType_t xClearOnExit, const BaseType_t xWaitForAllBits, TickType_t xTicksToWait) [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.

Example usage: #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.

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. A value of portMAX_DELAY can be used to block indefinitely (provided INCLUDE_vTaskSuspend is set to 1 in FreeRTOSConfig.h). - - Returns 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. - EventBits_t xEventGroupClearBits(EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToClear) Clear bits within an event group. This function cannot be called from an interrupt.

The event group in which the bits are to be cleared. 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. - - Returns The value of the event group before the specified bits were cleared. - EventBits_t xEventGroupSetBits(EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToSet) 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.

{ // 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. }

The event group in which the bits are to be set. 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. - - Returns 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. - EventBits_t xEventGroupSync(EventGroupHandle_t xEventGroup, const EventBits_t uxBitsToSet, const EventBits_t uxBitsToWaitFor, TickType_t xTicksToWait) 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.

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 synchronisation 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. //