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diff --git a/os/hal/dox/hal_spi.dox b/os/hal/dox/hal_spi.dox
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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 SPI SPI Driver
+ * @brief   Generic SPI Driver.
+ * @details This module implements a generic SPI (Serial Peripheral Interface)
+ *          driver allowing bidirectional and monodirectional transfers,
+ *          complex atomic transactions are supported as well.
+ * @pre     In order to use the SPI driver the @p HAL_USE_SPI option
+ *          must be enabled in @p halconf.h.
+ *
+ * @section spi_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=Helvetica, fontsize=8, fixedsize="true",
+          width="0.9", height="0.9"];
+    edge [fontname=Helvetica, fontsize=8];
+
+    stop  [label="SPI_STOP\nLow Power"];
+    uninit [label="SPI_UNINIT", style="bold"];
+    ready [label="SPI_READY\nClock Enabled"];
+    active [label="SPI_ACTIVE\nBus Active"];
+    complete [label="SPI_COMPLETE\nComplete"];
+
+    uninit -> stop [label="\n spiInit()", constraint=false];
+    stop -> ready [label="\nspiStart()"];
+    ready -> ready [label="\nspiSelect()\nspiUnselect()\nspiStart()"];
+    ready -> stop [label="\nspiStop()"];
+    stop -> stop [label="\nspiStop()"];
+    ready -> active [label="\nspiStartXXXI() (async)\nspiXXX() (sync)"];
+    active -> ready [label="\nsync return"];
+    active -> complete [label="\nasync callback\n>spc_endcb<"];
+    complete -> active [label="\nspiStartXXXI() (async)\nthen\ncallback return"];
+    complete -> ready [label="\ncallback return"];
+  }
+ * @enddot
+ * @else
+ * @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="SPI_STOP\nLow Power"];
+    uninit [label="SPI_UNINIT", style="bold"];
+    ready [label="SPI_READY\nClock Enabled"];
+    active [label="SPI_ACTIVE\nBus Active"];
+    complete [label="SPI_COMPLETE\nComplete"];
+
+    uninit -> stop [label="\n spiInit()", constraint=false];
+    stop -> ready [label="\nspiStart()"];
+    ready -> ready [label="\nspiSelect()\nspiUnselect()\nspiStart()"];
+    ready -> stop [label="\nspiStop()"];
+    stop -> stop [label="\nspiStop()"];
+    ready -> active [label="\nspiStartXXX() (async)\nspiXXX() (sync)"];
+    active -> ready [label="\nsync return"];
+    active -> complete [label="\nasync callback\n>spc_endcb<"];
+    complete -> active [label="\nspiStartXXXI() (async)\nthen\ncallback return"];
+    complete -> ready [label="\ncallback return"];
+  }
+ * @enddot
+ * @endif
+ *
+ * The driver is not thread safe for performance reasons, if you need to access
+ * the SPI bus from multiple threads then use the @p spiAcquireBus() and
+ * @p spiReleaseBus() APIs in order to gain exclusive access.
+ *
+ * @ingroup HAL_NORMAL_DRIVERS
+ */