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 /* SPDX-License-Identifier: BSD-2-Clause */
 
 /**
  * @file
  *
  * @ingroup RegulatorAPI
  *
  * @brief This header file defines the Regulator API.
  *
  */
 
 /*
  * Copyright (C) 2023 On-Line Applications Research Corporation (OAR)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
 /**
  * @defgroup RegulatorAPI Regulator API
  *
  * @brief Regulator APIs
  *
  * The Regulator provides a set of APIs to manage input sources which 
  * produces bursts of message traffic.
  *
  * The regulator is designed to sit logically between two entities -- a
  * source and a destination, where it limits the traffic sent to the
  * destination to prevent it from being flooded with messages from the
  * source. This can be used to accommodate bursts of input from a source
  * and meter it out to a destination.  The maximum number of messages
  * which can be buffered in the regulator is specified by the
  * @a maximum_messages field in the @a rtems_regulator_attributes
  * structure passed as an argument to @a rtems_regulator_create().
  *
  * The regulator library accepts an input stream of messages from a
  * source and delivers them to a destination. The regulator assumes that the
  * input stream from the source contains sporadic bursts of data which can
  * exceed the acceptable rate of the destination. By limiting the message rate,
  * the regulator prevents an overflow of messages.
  *
  * The regulator can be configured for the input buffering required to manage
  * the maximum burst and for the metering rate for the output. The output rate
  * is in messages per second. If the sender produces data too fast, the
  * regulator will buffer the configured number of messages.
  *
  * A configuration capability is provided to allow for adaptation to different
  * message streams. The regulator can also support running multiple instances,
  * which could be used on independent message streams.
  *
  * The regulator provides a simple interface to the application for avoiding
  * bursts of input from a fast source overflowing a slower destination.
  *
  * It is assumed that the application has a design limit on the number of
  * messages which may be buffered. All messages accepted by the regulator,
  * assuming no overflow on input, will eventually be output by the Delivery
  * thread.
  *
  * A regulator instance is used as follows from the producer/source side:
  *
  * @code
  *   while (1)
  *     use rtems_regulator_obtain_buffer to obtain a buffer
  *     input operation to fetch data into the buffer
  *     rtems_regulator_send(buffer, size of message)
  * @endcode
  *
  * The delivery of message buffers to the Destination and subsequent
  * release is performed in the context of the delivery thread by either
  * the delivery function or delivery thread. Details are below.
  *
  * The sequence diagram below shows the interaction between a message Source,
  * a Regulator instance, and RTEMS, given the usage described in the above
  * paragraphs.
  *
  * \startuml "Regulator Application Input Source Usage"
  *   Source -> Regulator : rtems_regulator_obtain_buffer(regulator, buffer)
  *   Regulator -> RTEMS : rtems_partition_get_buffer(id, buffer)
  *   RTEMS --> Regulator : rtems_status_code
  *   Regulator --> Source : rtems_status_code
  *   Source -> Regulator : rtems_regulator_send(regulator, message, length)
  *   Regulator -> RTEMS : rtems_message_queue_send(id, message, size)
  *   RTEMS --> Regulator : rtems_status_code
  *   Regulator --> Source : rtems_status_code
  * \enduml
  *
  * As illustrated in the sequence diagram, the Source usually corresponds
  * to application software reading a system input. The Source obtains a
  * buffer from the Regulator instance and fills it with incoming data.
  * The application explicitly obtaining a buffer and filling it in allows
  * for zero copy operations on the Source side.
  *
  * The Source then sends the buffer to the Regulator instance. The Regulator
  * the sends the buffer via a message queue which to the Delivery thread.
  * The Delivery thread executes periodically at a rate specified at
  * Regulation creation. At each period, the Delivery thread attempts to
  * receive up to a configured number of buffers and invoke the Delivery
  * function to deliver them to the Destination.
  *
  * The Delivery function is provided by the application for this
  * specific Regulator instance. Depending on the Destination, it may use
  * a function which copies the buffer contents (e.g., write()) or which
  * operates directly on the buffer contents (e.g. DMA from buffer). In
  * the case of a Destination which copies the buffer contents, the buffer
  * can be released via @a rtems_regulator_release_buffer() as soon as the
  * function or copying completes. In the case where the delivery uses the
  * buffer and returns, the call to @a rtems_regulator_release_buffer()
  * will occur when the use of the buffer is complete (e.g. completion
  * of DMA transfer).  This explicit and deliberate exposure of buffering
  * provides the application with the ability to avoid copying the contents.
  *
  * After the Source has sent the message to the Regulator instance,
  * the Source is free to process another input and the Regulator
  * instance will ensure that the buffer is delivered to the Delivery
  * function and Destination.
  *
  * The Regulator implementation uses the RTEMS Classic API Partition Manager
  * to manage the buffer pool and the RTEMS Classic API Message Queue
  * Manager to send the buffer to the Delivery thread.
  */
 
 #ifndef REGULATOR_H
 #define REGULATOR_H
 
 #include <stdlib.h>
 
 #include <rtems.h>
 
 /**
  * @ingroup RegulatorAPI
  *
  * @brief Regulator Delivery Function Type
  *
  * The user provides a function which is invoked to deliver a message
  * to the output. It is invoked by the Delivery thread created as part
  * of @a rtems_regulator_create(). The priority and stack size of the
  * Delivery thread are specified in the regulator attribute set.
  *
  * It takes three parameters:
  *
  * @param[in] context is an untyped pointer to a user context
  * @param[in] message points to the message
  * @param[in] length is the message size
  *
  * The following is an example deliverer function. It assumes that the
  * application has defined the my_context_t structure and it has at least
  * the socket field. The @a message passed in originated with an
  * application source which obtained the @a message buffer using
  * @a rtems_regulator_obtain_buffer(), filled it in with source data,
  * and used @a rtems_regulator_send() to hand to the regulator instance
  * for later delivery.
  *
  * @code
  *   bool my_deliverer(
  *     void     *context,
  *     void     *message,
  *     size_t    length
  *    )
  *    {
  *       my_context_t *my_context;
  *
  *       my_context = (my_context_t *)context;
  *
  *       write(my_context->socket, message, length);
  *       rtems_regulator_release_buffer(message);
  *       // return false to indicate we released the buffer
  *       return false;
  *     }
  * @endcode
  *
  * The delivery function returns true to indicate that the delivery thread
  * should release the buffer or false to indicate that it released the
  * buffer.  If the delivery function invokes a function like @a write()
  * to deliver the message to the destination, then the buffer can be
  * released immediately after the call. If the delivery function does
  * something like setting up a DMA transfer of the buffer, it cannot be
  * released until after the DMA is complete.
  *
  * The following sequence diagram shows the behavior of the Delivery thread
  * body and its interaction with the user-supplied deliverer() function.
  *
  * \startuml "Regulator Delivery Thread Body"
  *   loop while (1)
  *     "Delivery Thread" -> RTEMS : rtems_rate_monotonic_period(id, delivery_thread_period)
  *     loop for 0 : maximum_to_dequeue_per_period
  *       "Delivery Thread" -> RTEMS : rtems_message_queue_receive(id, message, size, wait, 0)
  *       RTEMS --> "Delivery Thread" : rtems_status_code
  *       group if [rtems_status_code != RTEMS_SUCCESSFUL]
  *         RTEMS -> "Delivery Thread" : break
  *       end
  *       "Delivery Thread" -> Application : deliverer(context, buffer, length)
  *       "Delivery Thread" -> RTEMS : rtems_partition_return_buffer(id, buffer)
  *       RTEMS --> "Delivery Thread" : rtems_status_code
  *     end
  *   end
  * \enduml
  *
  * In the above sequence diagram, the key points are:
  *
  *   -# The Delivery Thread Body is periodically executed.
  *   -# During each period, up to the instance configuration parameter
  *      @a maximum_to_dequeue_per_period may be dequeued and
  *      passed the application's delivery function for processing.
  *
  * Note that the application explicitly obtains buffers from the
  * regulator instance but that the release may be done by Delivery
  * Thread, the Delivery function, or later when the buffer contents
  * are transferred.
  */
 typedef bool (*rtems_regulator_deliverer)(
   void     *context,
   void     *message,
   size_t    length
 );
 
 /**
  * @ingroup RegulatorAPI
  *
  * @brief Attributes for Regulator Instance
  *
  * An instance of this structure must be populated by the application
  * before creating an instance of the regulator. These settings tailor
  * the behavior of the regulator instance.
  */
 typedef struct {
   /** Application function to invoke to output a message to the destination*/
   rtems_regulator_deliverer deliverer;
 
   /** Context pointer to pass to deliver function */
   void  *deliverer_context;
 
   /** Maximum size message to process */
   size_t  maximum_message_size;
 
   /** Maximum number of messages to be able to buffer */
   size_t  maximum_messages;
 
   /** Priority of Delivery thread */
   rtems_task_priority delivery_thread_priority;
 
   /** Stack size of Delivery thread */
   size_t delivery_thread_stack_size;
 
   /** Period (in ticks) of Delivery thread */
   rtems_interval delivery_thread_period;
 
   /** Maximum messages to dequeue per period */
   size_t  maximum_to_dequeue_per_period;
 
 } rtems_regulator_attributes;
 
 /**
  * @ingroup RegulatorAPI
  *
  * @brief Statistics for Regulator Instance
  *
  * An instance of this structure is provided to the directive
  * @a rtems_regulator_get_statistics and is filled in by that service.
  */
 typedef struct {
   /** Number of successfully obtained buffers. */
   size_t    obtained;
   
   /** Number of successfully released buffers. */
   size_t    released;
 
   /** Number of successfully delivered buffers. */
   size_t    delivered;
 
   /** Rate Monotonic Period statistics for Delivery Thread */
   rtems_rate_monotonic_period_statistics period_statistics;
 
 } rtems_regulator_statistics;
 
 /**
  * @ingroup RegulatorAPI
  *
  * @brief Regulator Internal Structure
  */
 struct _Regulator_Control;
 
 /**
  * @ingroup RegulatorAPI
  *
  * @brief Regulator Instance
  *
  * This is used by the application as the handle to a Regulator instance.
  */
 typedef struct _Regulator_Control *rtems_regulator_instance;
 
 /**
  * @ingroup RegulatorAPI
  *
  * @brief Create a regulator
  *
  * This function creates an instance of a regulator. It uses the provided
  * @a attributes to create the instance return in @a regulator. This instance
  * will allocate the buffers associated with the regulator instance as well
  * as the Delivery thread.
  *
  * The @a attributes structure defines the priority and stack size of
  * the Delivery thread dedicated to this regulator instance. It also
  * defines the period of the Delivery thread and the maximum number of
  * messages that may be delivered per period via invocation of the
  * delivery function. 
  *
  * For each regulator instance, the following resources are allocated:
  *
  * - A memory area for the regulator control block using @a malloc().
  * - A RTEMS Classic API Message Queue is constructed with message 
  *   buffer memory allocated using @a malloc().  Each message consists
  *   of a pointer and a length.
  * - A RTEMS Classic API Partition.
  * - A RTEMS Classic API Rate Monotonic Period.
  *
  * @param[in] attributes specify the regulator instance attributes
  * @param[inout] regulator will point to the regulator instance
  *
  * @return an RTEMS status code indicating success or failure.
  *
  * @note This function allocates memory for the buffers holding messages,
  *       an Delivery thread and an RTEMS partition. When it executes, the
  *       Delivery thread will create an RTEMS rate monotonic period.
  */
 rtems_status_code rtems_regulator_create(
   rtems_regulator_attributes  *attributes,
   rtems_regulator_instance   **regulator
 );
 
 /**
  * @ingroup RegulatorAPI
  *
  * @brief Delete a regulator
  *
  * This function is used to delete the specified @a regulator instance.
  *
  * It is the responsibility of the user to ensure that any resources
  * such as sockets or open file descriptors used by the delivery
  * function are also deleted. It is likely safer to delete those 
  * delivery resources after deleting the regulator instance rather than
  * before.
  *
  * @param[in] regulator is the instance to delete
  * @param[in] ticks is the maximum number of ticks to wait for
  *            the delivery thread to shutdown.
  *
  * @return an RTEMS status code indicating success or failure.
  *
  * @note This function deallocates the resources allocated during
  *       @a rtems_regulator_create().
  */
 rtems_status_code rtems_regulator_delete(
   rtems_regulator_instance    *regulator,
   rtems_interval               ticks
 );
 
 /**
  * @ingroup RegulatorAPI
  *
  * @brief Obtain Buffer from Regulator
  *
  * This function is used to obtain a buffer from the regulator's pool. The
  * @a buffer returned is assumed to be filled in with contents and used
  * in a subsequent call to @a rtems_regulator_send(). When the @a buffer is
  * delivered, it is expected to be released. If the @a buffer is not
  * successfully accepted by this function,  then it should be returned
  * using @a rtems_regulator_release_buffer() or used to send another message.
  *
  * The @a buffer is of the maximum_message_size specified in the attributes
  * passed in to @a rtems_regulator_create().
  *
  * @param[in] regulator is the regulator instance to operate upon
  * @param[out] buffer will point to the allocated buffer
  *
  * @return an RTEMS status code indicating success or failure.
  *
  * @note This function does not perform dynamic allocation. It obtains a
  *       buffer from the pool allocated during @a rtems_regulator_create().
  *
  * @note Any attempt to write outside the buffer area is undefined.
  */
 rtems_status_code rtems_regulator_obtain_buffer(
   rtems_regulator_instance   *regulator,
   void                      **buffer
 );
 
 /**
  * @ingroup RegulatorAPI
  *
  * @brief Release Previously Obtained Regulator Buffer
  *
  * This function is used to release a buffer to the regulator's pool. It is
  * assumed that the @a buffer returned will not be used by the application
  * anymore. The @a buffer must have previously been allocated by
  * @a rtems_regulator_obtain_buffer() and NOT passed to
  * @a rtems_regulator_send().
  *
  * If a subsequent @a rtems_regulator_send() using this @a buffer is
  * successful, the @a buffer will eventually be processed by the delivery
  * thread and released.
  *
  * @param[in] regulator is the regulator instance to operate upon
  * @param[out] buffer will point to the buffer to release
  *
  * @return an RTEMS status code indicating success or failure.
  *
  * @note This function does not perform dynamic deallocation. It releases a
  *       buffer to the pool allocated during @a rtems_regulator_create().
  */
 rtems_status_code rtems_regulator_release_buffer(
   rtems_regulator_instance   *regulator,
   void                       *buffer
 );
 
 /**
  * @ingroup RegulatorAPI
  *
  * @brief Send to regulator instance
  *
  * This function is used by the producer to send a @a message to the
  * @a regulator for later delivery by the Delivery thread. The message is
  * contained in the memory pointed to by @a message and is @a length
  * bytes in length.
  *
  * It is required that the @a message buffer was obtained via
  * @a rtems_regulator_obtain_buffer().
  *
  * It is assumed that the @a message buffer has been filled in with
  * application content to deliver.
  *
  * If the @a rtems_regulator_send() is successful, the buffer is enqueued
  * inside the regulator instance for subsequent delivery. After the
  * @a message is delivered, it may be released by either delivery
  * function or the application code depending on the implementation.
  *
  * The status @a RTEMS_TOO_MANY is returned if the regulator's
  * internal queue is full. This indicates that the configured
  * maximum number of messages was insufficient. It is the
  * responsibility of the caller to decide whether to hold messages,
  * drop them, or print a message that the maximum number of messages
  * should be increased.
  *
  * If @a rtems_regulator_send() is unsuccessful, it is the application's
  * responsibility to release the buffer. If it is successfully sent,
  * then it becomes the responsibility of the delivery function to
  * release it.
  *
  * @param[in] regulator is the regulator instance to operate upon
  * @param[out] message points to the message to deliver
  * @param[out] length is the size of the message in bytes
  *
  * @return an RTEMS status code indicating success or failure.
  *
  */
 rtems_status_code rtems_regulator_send(
   rtems_regulator_instance  *regulator,
   void                      *message,
   size_t                     length
 );
 
 /**
  * @ingroup RegulatorAPI
  *
  * @brief Obtain statistics for regulator instance
  *
  * This function is used by the application to obtain statistics
  * information about the regulator instance.  
  *
  * If the @a obtained and @a released fields in the returned 
  * @a statistics structure are equal, then there are no buffers
  * outstanding from this regulator instance.
  *
  * @param[in] regulator is the regulator instance to operate upon
  * @param[inout] statistics points to the statistics structure to fill in
  *
  * @return an RTEMS status code indicating success or failure.
  *
  */
 rtems_status_code rtems_regulator_get_statistics(
   rtems_regulator_instance   *regulator,
   rtems_regulator_statistics *statistics
 );
 
 #endif /* REGULATOR_H */

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