/*
    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 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_idle -> tx_active [label="\nuartStartSend()"];
    tx_idle -> tx_idle [label="\nuartStopSend()\n>txend2_cb<"];
    tx_active -> tx_complete [label="\nbuffer transmitted\n>txend1_cb<"];
    tx_active -> tx_idle [label="\nuartStopSend()"];
    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_idle -> rx_idle [label="\nuartStopReceive()\n>rxchar_cb<\n>rxerr_cb<"];
    rx_idle -> rx_active [label="\nuartStartReceive()"];

    rx_active -> rx_complete [label="\nbuffer filled\n>rxend_cb<"];
    rx_active -> rx_idle [label="\nuartStopReceive()"];
    rx_active -> rx_active [label="\nreceive error\n>rxerr_cb<"];
    rx_complete -> rx_active [label="\nuartStartReceiveI()"];
    rx_complete -> rx_idle [label="\ncallback return"];
  }
 * @enddot
 *
 * @ingroup HAL_NORMAL_DRIVERS
 */