/*
    ChibiOS - Copyright (C) 2006..2015 Giovanni Di Sirio.

    This file is part of ChibiOS.

    ChibiOS is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.

    ChibiOS is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

/**
 * @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 @<driver@>.c, the HLD implementation file. This file must be
 *     included in the Makefile in order to use the driver.
 *   - @p @<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 @<driver@>_lld.c, the LLD implementation file. This file must be
 *     included in the Makefile in order to use the driver.
 *   - @p @<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
 * @brief   HAL Interfaces.
 *
 * @ingroup IO
 */

/**
 * @defgroup HAL_INNER_CODE Inner Code
 * @brief   HAL Inner 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
 */