/*
    ChibiOS - Copyright (C) 2006..2016 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 GPT GPT Driver
 * @brief   Generic GPT Driver.
 * @details This module implements a generic GPT (General Purpose Timer)
 *          driver. The timer can be programmed in order to trigger callbacks
 *          after a specified time period or continuously with a specified
 *          interval.
 * @pre     In order to use the GPT driver the @p HAL_USE_GPT option
 *          must be enabled in @p halconf.h.
 *
 * @section gpt_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];

    stop  [label="GPT_STOP\nLow Power"];
    uninit [label="GPT_UNINIT", style="bold"];
    ready [label="GPT_READY\nClock Enabled"];
    continuous [label="GPT_CONT..S\nContinuous\nMode"];
    oneshot [label="GPT_ONESHOT\nOne Shot\nMode"];

    uninit -> stop [label=" gptInit()", constraint=false];
    stop -> stop [label="\ngptStop()"];
    stop -> ready [label="\ngptStart()"];
    ready -> stop [label="\ngptStop()"];
    ready -> ready [label="\ngptStart()"];
    ready -> continuous [label="\ngptStartContinuous()"];
    continuous -> ready [label="\ngptStopTimer()"];
    continuous -> continuous [label=">callback<"];
    ready -> oneshot [label="\ngptStartOneShot()\ngptPolledDelay()"];
    oneshot -> ready [label="\n>callback<\nor\nDelay Over"];
  }
 * @enddot
 *
 * @section gpt_2 GPT Operations.
 * This driver abstracts a generic timer composed of:
 * - A clock prescaler.
 * - A main up counter.
 * - A comparator register that resets the main counter to zero when the limit
 *   is reached. A callback is invoked when this happens.
 * .
 * The timer can operate in three different modes:
 * - <b>Continuous Mode</b>, a periodic callback is invoked until the driver
 *   is explicitly stopped.
 * - <b>One Shot Mode</b>, a callback is invoked after the programmed period
 *   and then the timer automatically stops.
 * - <b>Delay Mode</b>, the timer is used for inserting a brief delay into
 *   the execution flow, no callback is invoked in this mode.
 * .
 * @ingroup HAL_NORMAL_DRIVERS
 */