/*
    ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010 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/>.
*/

/**
 * @defgroup USB USB Driver
 * @brief Generic USB Driver.
 * @details This module implements a generic USB driver.
 * @pre     In order to use the USB driver the @p HAL_USE_USB option
 *          must be enabled in @p halconf.h.
 *
 * @section usb_1 Driver State Machine
 * The driver implements a state machine internally, not all the driver
 * functionalities can be used in any moment, any transition not explicitly
 * shown in the following diagram has to be considered an error and shall
 * be captured by an assertion (if enabled).
 * @if LATEX_PDF
 * @else
 * @endif
 *
 * @section usb_2 USB Operations
 * The USB driver is quite complex and USB is complex in itself, it is
 * recommended to study the USB specification before trying to use the
 * driver.
 *
 * @subsection usb_2_1 USB Implementation
 * The USB driver abstracts the inner details of the underlying USB hardware.
 * The driver works asynchronously and communicates with the application
 * using callbacks. The application is responsible of the descriptors and
 * strings required by the USB device class to be implemented and of the
 * handling of the specific messages sent over the endpoint zero. Standard
 * messages are handled internally to the driver. The application can use
 * hooks in order to handle custom messages or override the handling of the
 * default handling of standard messages.
 *
 * @subsection usb_2_2 USB Endpoints
 * USB endpoints are the objects that the application uses to exchange
 * data with the host. There are two kind of endpoints:
 * - <b>IN</b> endpoints are used by the application to transmit data to
 *   the host.
 * - <b>OUT</b> endpoints are used by the application to receive data from
 *   the host.
 * .
 * In ChibiOS/RT the endpoints can be configured in two distinct ways:
 * - <b>Packet Mode</b>. In this mode the driver invokes a callback each
 *   time a packet has been received or transmitted. This mode is especially
 *   suited for those applications handling continuous streams of data.
 * - <b>Transaction Mode</b>. In this mode the driver invokes a callback
 *   only after a large, potentially multi-packet, transfer has been
 *   completed, a callback is invoked only at the end of the transfer.
 *   .
 * .
 * @subsection usb_2_3 USB Callbacks
 * The USB driver uses callbacks in order to interact with the application.
 * There are several kind of callbacks to be handled:
 * - Driver-wide events callback. As example errors, suspend event, reset
 *   event etc.
 * - Messages hook callback. This hook allows the application to implement
 *   handling of custom messages or to override the default handling of
 *   standard messages.
 * - Descriptor requested callback. When the driver endpoint zero handler
 *   needs to serve a descriptor to the host it queries the application
 *   using this callback.
 * - Start of Frame callback. This callback is invoked each time a SOF
 *   packet is received.
 * - Endpoint callbacks. Each endpoint informs the application about I/O
 *   conditions using those callbacks.
 * .
 *
 * @ingroup IO
 */