/*
    ChibiOS - Copyright (C) 2006..2018 Giovanni Di Sirio

    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at

        http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
*/

/**
 * @defgroup IO HAL
 * @brief   Hardware Abstraction Layer.
 * @details Under ChibiOS the set of the various device driver interfaces
 * is called the HAL subsystem: Hardware Abstraction Layer. The HAL is the
 * abstract interface between ChibiOS applications and hardware.
 *
 * @section hal_device_driver_arch HAL Device Drivers Architecture
 * The HAL contains several kind of modules:
 * - Normal Device Drivers
 * - Complex Device Drivers
 * - Interfaces
 * - Inner Code
 * .
 * @section hal_normal_device_drivers HAL Normal Device Drivers
 * Normal device are meant to interface the application to the underlying
 * hardware through an high level API. Normal Device Drivers are split in two
 * layers:
 * - High Level Device Driver (<b>HLD</b>). This layer contains the definitions
 *   of the driver's APIs and the platform independent part of the driver.<br>
 *   An HLD is composed by two files:
 *   - @p hal_@<driver@>.c, the HLD implementation file. This file must be
 *     included in the Makefile in order to use the driver.
 *   - @p hal_@<driver@>.h, the HLD header file. This file is implicitly
 *     included by the HAL header file @p hal.h.
 *   .
 * - Low Level Device Driver (<b>LLD</b>). This layer contains the platform
 *   dependent part of the driver.<br>
 *   A LLD is composed by two files:
 *   - @p hal_@<driver@>_lld.c, the LLD implementation file. This file must be
 *     included in the Makefile in order to use the driver.
 *   - @p hal_@<driver@>_lld.h, the LLD header file. This file is implicitly
 *     included by the HLD header file.
 *   .
 * .
 * @subsection hal_device_driver_diagram Diagram
 * @dot
  digraph example {
    graph [size="5, 7", pad="1.5, 0"];
    node [shape=rectangle, fontname=Helvetica, fontsize=8,
          fixedsize="true", width="2.0", height="0.4"];
    edge [fontname=Helvetica, fontsize=8];

    app [label="Application"];
    hld [label="High Level Driver"];
    lld [label="Low Level Driver"];
    hw [label="Microcontroller Hardware"];
    hal_lld [label="HAL shared low level code"];

    app->hld;
    hld->lld;
    lld-> hw;
    lld->hal_lld;
    hal_lld->hw;
  }
 * @enddot
 *
 * @section hal_complex_device_drivers HAL Complex Device Drivers
 * It is a class of device drivers that offer an high level API but do not
 * use the hardware directly. Complex device drivers use other drivers for
 * accessing the machine resources.
 *
 * @section hal_interfaces HAL Interfaces
 * An interface is a binary structure allowing the access to a service
 * using virtual functions. This allows to create drivers that can be
 * accessed using a common interface.
 * The concept of interface is commonly found in object-oriented languages
 * like Java or C++, their meaning in ChibiOS/HAL is exactly the same.
 *
 * @section hal_inner_code HAL Inner Code
 * Some modules are shared among multiple device drivers and are not
 * necessarily meant to be used by the application layer.
 */

/**
 * @defgroup HAL_CONF Configuration
 * @brief   HAL Configuration.
 * @details The file @p halconf.h contains the high level settings for all
 * the drivers supported by the HAL. The low level, platform dependent,
 * settings are contained in the @p mcuconf.h file instead and are describe
 * in the various platforms reference manuals.
 *
 * @ingroup IO
 */

/**
 * @defgroup HAL_NORMAL_DRIVERS Normal Drivers
 * @brief   HAL Normal Drivers.
 *
 * @ingroup IO
 */

/**
 * @defgroup HAL_COMPLEX_DRIVERS Complex Drivers
 * @brief   HAL Complex Drivers.
 *
 * @ingroup IO
 */

/**
 * @defgroup HAL_INTERFACES Interfaces and Classes
 * @brief   HAL Interfaces and Classes.
 *
 * @ingroup IO
 */
 
/**
 * @defgroup HAL_INNER_CODE Inner Code
 * @brief   HAL Inner Code.
 *
 * @ingroup IO
 */

/**
 * @defgroup HAL_SUPPORT Support Code
 * @brief   HAL Support Code.
 *
 * @ingroup IO
 */

/**
 * @defgroup OSAL OSAL
 * @brief   Operating System Abstraction Layer.
 * @details <h2>The OSAL</h2>
 *          The OSAL is the link between ChibiOS/HAL and services
 *          provided by operating systems like:
 *          - Critical Zones handling.
 *          - Interrupts handling.
 *          - Runtime Errors management.
 *          - Inter-task synchronization.
 *          - Task-ISR synchronization.
 *          - Time management.
 *          - Events.
 *          .
 *          ChibiOS/HAL is designed to tightly integrate with the underlying
 *          RTOS in order to provide the best experience to developers and
 *          minimize integration issues.<br>
 *          This section describes the API that OSALs are expected to expose
 *          to the HAL.
 *
 *          <h2>RTOS Requirements</h2>
 *          The OSAL API closely resembles the ChibiOS/RT API, for obvious
 *          reasons, however an OSAL module can be implemented for any
 *          reasonably complete RTOS or even a RTOS-less bare metal
 *          machine, if required.<br>
 *          In order to be able to support an HAL an RTOS should support the
 *          following minimal set of features:
 *          - Task-level critical zones API.
 *          - ISR-level critical zones API, only required on those CPU
 *            architectures supporting preemptable ISRs like Cortex-Mx
 *            cores.
 *          - Ability to invoke API functions from inside a task critical
 *            zone. Functions that are required to support this feature are
 *            marked with an "I" or "S" letter at the end of the name.
 *          - Ability to invoke API functions from inside an ISR critical
 *            zone. Functions that are required to support this feature are
 *            marked with an "I" letter at the end of the name.
 *          - Tasks Queues or Counting Semaphores with Timeout capability.
 *          - Ability to suspend a task and wakeup it from ISR with Timeout
 *            capability.
 *          - Event flags, the mechanism can be simulated using callbacks in
 *            case the RTOS does not support it.
 *          - Mutual Exclusion mechanism like Semaphores or Mutexes.
 *          .
 *          All the above requirements can be satisfied even on naked HW with
 *          a very think SW layer. In case that the HAL is required to work
 *          without an RTOS.
 *
 *          <h2>Supported RTOSes</h2>
 *          The RTOSes supported out of the box are:
 *          - ChibiOS/RT
 *          - ChibiOS/NIL
 *          .
 *          Implementations have also been successfully created on RTOSes not
 *          belonging to the ChibiOS products family but are not supported
 *          as a core feature of ChibiOS/HAL.
 *
 * @ingroup IO
 */