/*
    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 ICU ICU Driver
 * @brief   Generic ICU Driver.
 * @details This module implements a generic ICU (Input Capture Unit) driver.
 *          The purpose of the driver is to measure period and duty cycle of
 *          an input digital signal (PWM input).
 * @pre     In order to use the ICU driver the @p HAL_USE_ICU option
 *          must be enabled in @p halconf.h.
 *
 * @section icu_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
 * @dot
  digraph example {
    size="5, 7";
    rankdir="LR";

    node [shape=circle, fontname=Sans, fontsize=8, fixedsize="true", width="0.9", height="0.9"];
    edge [fontname=Sans, fontsize=8];

    stop  [label="ICU_STOP\nLow Power"];
    uninit [label="ICU_UNINIT", style="bold"];
    ready [label="ICU_READY\nClock Enabled"];
    waiting [label="ICU_WAITING"];
    active [label="ICU_ACTIVE"];

    uninit -> stop [label=" icuInit()", constraint=false];
    stop -> stop [label="\nicuStop()"];
    stop -> ready [label="\nicuStart()"];
    ready -> stop [label="\nicuStop()"];
    ready -> ready [label="\nicuStart()\nicuStopCapture()"];
    ready -> waiting [label="\nicuStartCapture()"];
    waiting -> active [label="\nFirst Activation Edge\nicuWaitCapture()"];
    waiting -> ready [label="\nicuStopCapture()"];
    active -> ready [label="\nicuStopCapture()"];
    active -> active [label="\nActivation Edge\n>period_cb<"];
    active -> active [label="\nDe-activation Edge\n>width_cb<"];
  }
 * @enddot
 * @else
 * @dot
  digraph example {
    rankdir="LR";

    node [shape=circle, fontname=Sans, fontsize=8, fixedsize="true", width="0.9", height="0.9"];
    edge [fontname=Sans, fontsize=8];

    stop  [label="ICU_STOP\nLow Power"];
    uninit [label="ICU_UNINIT", style="bold"];
    ready [label="ICU_READY\nClock Enabled"];
    waiting [label="ICU_WAITING"];
    active [label="ICU_ACTIVE"];

    uninit -> stop [label=" icuInit()", constraint=false];
    stop -> stop [label="\nicuStop()"];
    stop -> ready [label="\nicuStart()"];
    ready -> stop [label="\nicuStop()"];
    ready -> ready [label="\nicuStart()\nicuStopCapture()"];
    ready -> waiting [label="\nicuStartCapture()"];
    waiting -> active [label="\nFirst Activation Edge\nicuWaitCapture()"];
    waiting -> ready [label="\nicuStopCapture()"];
    active -> ready [label="\nicuStopCapture()"];
    active -> active [label="\nActivation Edge\n>period_cb<"];
    active -> active [label="\nDe-activation Edge\n>width_cb<"];
  }
 * @enddot
 * @endif
 *
 * @section icu_2 ICU Operations.
 * This driver abstracts a generic Input Capture Unit composed of:
 * - A clock prescaler.
 * - A main up counter.
 * - Two capture registers triggered by the rising and falling edges on
 *   the sampled input.
 * .
 * The ICU unit can be programmed to synchronize on the rising or falling
 * edge of the sample input:
 * - <b>ICU_INPUT_ACTIVE_HIGH</b>, a rising edge is the start signal.
 * - <b>ICU_INPUT_ACTIVE_LOW</b>, a falling edge is the start signal.
 * .
 * Callbacks are optionally invoked when:
 * - On the PWM de-activation edge.
 * - On the PWM activation edge, measurements for the previous cycle are
 *   available from this callback and can be retrieved using
 *   @p icuGetPeriodX() and @p icuGetWidthX().
 * .
 * @ingroup HAL_NORMAL_DRIVERS
 */