/*
    ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010,
                 2011,2012 Giovanni Di Sirio.

    This file is part of ChibiOS/RT.

    ChibiOS/RT 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/RT 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/>.

                                      ---

    A special exception to the GPL can be applied should you wish to distribute
    a combined work that includes ChibiOS/RT, without being obliged to provide
    the source code for any proprietary components. See the file exception.txt
    for full details of how and when the exception can be applied.
*/

/**
 * @defgroup IO HAL
 * @brief Hardware Abstraction Layer.
 * @details Under ChibiOS/RT the set of the various device driver interfaces
 * is called the HAL subsystem: Hardware Abstraction Layer. The HAL is the
 * abstract interface between ChibiOS/RT application and hardware.
 *
 * @section hal_device_driver_arch HAL Device Drivers Architecture
 * A device driver is usually 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.
 *   .
 *   The LLD may be not present in those drivers that do not access the
 *   hardware directly but through other device drivers, as example the
 *   MMC_SPI driver uses the SPI and PAL drivers in order to implement
 *   its functionalities.
 * .
 * @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
 */

/**
 * @defgroup HAL_CONF Configuration
 * @brief @ref 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
 */