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+/*
+    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 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
+ */