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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 PWM PWM Driver
+ * @brief   Generic PWM Driver.
+ * @details This module implements a generic PWM (Pulse Width Modulation)
+ *          driver.
+ * @pre     In order to use the PWM driver the @p HAL_USE_PWM option
+ *          must be enabled in @p halconf.h.
+ *
+ * @section pwm_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="PWM_UNINIT", style="bold"];
+    stop  [label="PWM_STOP\nLow Power"];
+    ready [label="PWM_READY\nClock Enabled"];
+    uninit -> stop [label="pwmInit()"];
+    stop -> stop [label="pwmStop()"];
+    stop -> ready [label="pwmStart()"];
+    ready -> stop [label="pwmStop()"];
+    ready -> ready [label="pwmEnableChannel()\npwmDisableChannel()"];
+  }
+ * @enddot
+ *
+ * @section pwm_2 PWM Operations.
+ * This driver abstracts a generic PWM 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. An optional callback can be generated when this happens.
+ * - An array of @p PWM_CHANNELS PWM channels, each channel has an output,
+ *   a comparator and is able to invoke an optional callback when a comparator
+ *   match with the main counter happens.
+ * .
+ * A PWM channel output can be in two different states:
+ * - <b>IDLE</b>, when the channel is disabled or after a match occurred.
+ * - <b>ACTIVE</b>, when the channel is enabled and a match didn't occur yet
+ *   in the current PWM cycle.
+ * .
+ * Note that the two states can be associated to both logical zero or one in
+ * the @p PWMChannelConfig structure.
+ *
+ * @ingroup HAL_NORMAL_DRIVERS
+ */