/*
    ChibiOS - Copyright (C) 2006,2007,2008,2009,2010,
              2011,2012,2013,2014 Giovanni Di Sirio.

    This file is part of ChibiOS/HAL 

    ChibiOS/HAL 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 UART UART Driver
 * @brief   Generic UART Driver.
 * @details This driver abstracts a generic UART (Universal Asynchronous
 *          Receiver Transmitter) peripheral, the API is designed to be:
 *          - Unbuffered and copy-less, transfers are always directly performed
 *            from/to the application-level buffers without extra copy
 *            operations.
 *          - Asynchronous, the API is always non blocking.
 *          - Callbacks capable, operations completion and other events are
 *            notified using callbacks.
 *          .
 *          Special hardware features like deep hardware buffers, DMA transfers
 *          are hidden to the user but fully supportable by the low level
 *          implementations.<br>
 *          This driver model is best used where communication events are
 *          meant to drive an higher level state machine, as example:
 *          - RS485 drivers.
 *          - Multipoint network drivers.
 *          - Serial protocol decoders.
 *          .
 *          If your application requires a synchronous buffered driver then
 *          the @ref SERIAL should be used instead.
 * @pre     In order to use the UART driver the @p HAL_USE_UART option
 *          must be enabled in @p halconf.h.
 *
 * @section uart_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).
 * @dot
  digraph example {
    rankdir="LR";
    node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.9", height="0.9"];
    edge [fontname=Helvetica, fontsize=8];

    uninit [label="UART_UNINIT", style="bold"];
    stop  [label="UART_STOP\nLow Power"];
    ready [label="UART_READY\nClock Enabled"];

    uninit -> stop [label="\nuartInit()"];
    stop -> ready [label="\nuartStart()"];
    ready -> ready [label="\nuartStart()"];
    ready -> stop [label="\nuartStop()"];
    stop -> stop [label="\nuartStop()"];
  }
 * @enddot
 *
 * @subsection uart_1_1 Transmitter sub State Machine
 * The follow diagram describes the transmitter state machine, this diagram
 * is valid while the driver is in the @p UART_READY state. This state
 * machine is automatically reset to the @p TX_IDLE state each time the
 * driver enters the @p UART_READY state.
 * @dot
  digraph example {
    rankdir="LR";
    node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.9", height="0.9"];
    edge [fontname=Helvetica, fontsize=8];

    tx_idle [label="TX_IDLE", style="bold"];
    tx_active [label="TX_ACTIVE"];
    tx_complete [label="TX_COMPLETE"];
    tx_fatal [label="Fatal Error", style="bold"];

    tx_idle -> tx_active [label="\nuartStartSend()"];
    tx_idle -> tx_idle [label="\nuartStopSend()\n>uc_txend2<"];
    tx_active -> tx_complete [label="\nbuffer transmitted\n>uc_txend1<"];
    tx_active -> tx_idle [label="\nuartStopSend()"];
    tx_active -> tx_fatal [label="\nuartStartSend()"];
    tx_complete -> tx_active [label="\nuartStartSendI()\nthen\ncallback return"];
    tx_complete -> tx_idle [label="\ncallback return"];
  }
 * @enddot
 *
 * @subsection uart_1_2 Receiver sub State Machine
 * The follow diagram describes the receiver state machine, this diagram
 * is valid while the driver is in the @p UART_READY state. This state
 * machine is automatically reset to the @p RX_IDLE state each time the
 * driver enters the @p UART_READY state.
 * @dot
  digraph example {
    rankdir="LR";
    node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.9", height="0.9"];
    edge [fontname=Helvetica, fontsize=8];

    rx_idle [label="RX_IDLE", style="bold"];
    rx_active [label="RX_ACTIVE"];
    rx_complete [label="RX_COMPLETE"];
    rx_fatal [label="Fatal Error", style="bold"];

    rx_idle -> rx_idle [label="\nuartStopReceive()\n>uc_rxchar<\n>uc_rxerr<"];
    rx_idle -> rx_active [label="\nuartStartReceive()"];

    rx_active -> rx_complete [label="\nbuffer filled\n>uc_rxend<"];
    rx_active -> rx_idle [label="\nuartStopReceive()"];
    rx_active -> rx_active [label="\nreceive error\n>uc_rxerr<"];
    rx_active -> rx_fatal [label="\nuartStartReceive()"];
    rx_complete -> rx_active [label="\nuartStartReceiveI()\nthen\ncallback return"];
    rx_complete -> rx_idle [label="\ncallback return"];
  }
 * @enddot
 *
 * @ingroup IO
 */