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+/*

+    ChibiOS/HAL - 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 IO

+ */