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+.. highlight:: cpp
+
+.. _usb:
+
+USB
+===
+
+The STM32 microprocessors include a dedicated USB peripheral which can
+be configured to act as a general USB slave device with transfer rates
+up to 12Mbps. (It unfortunately can't be configured as a host or
+on-the-go device).  By default, the peripheral is configured for two
+uses: first, to receive sketch/program uploads from the :ref:`IDE
+<ide>`, and second, to emulate a regular serial port for use as a
+terminal (text read/write).
+
+The emulated terminal is relatively slow and inefficient; it is best
+for transferring data at regular serial speeds (kilobaud).  Library
+support for accessing the emulated terminal is available at the
+:ref:`SerialUSB <lang-serialusb>` reference.
+
+The SerialUSB channel is used with the :ref:`Maple bootloader
+<bootloader>` to reprogram the board: a :ref:`magic sequence of
+control line toggles and transmitted data <bootloader-rev3>` causes a
+Maple to reset itself and enter bootloader mode. As an unfortunate
+consequence, the auto-reset will not work if the IDE can not access
+the serial port, either due to a conflict with another program (serial
+monitor) or because the interface has been disabled from the Maple
+side (through :ref:`SerialUSB.end() <lang-serialusb-end>`).  A
+solution to the second problem is the use of :ref:`perpetual
+bootloader mode <troubleshooting-perpetual-bootloader>`.
+
+Recommended Reading
+-------------------
+
+* `USB in a Nutshell <http://www.beyondlogic.org/usbnutshell/usb1.shtml>`_, an overview from Beyond Logic
+* `USB made simple <http://www.usbmadesimple.co.uk/>`_, an illustrated series of articles on USB
+* The `USB 2.0 Specification <http://www.usb.org/developers/docs/>`_ (`direct link <http://www.usb.org/developers/docs/usb_20_070113.zip>`_)
+* `Embedded USB - a brief tutorial <http://www.computer-solutions.co.uk/info/Embedded_tutorials/usb_tutorial.htm>`_
+* `Wikipedia article on Universal Serial Bus (USB) <http://en.wikipedia.org/wiki/Universal_Serial_Bus>`_
+* Linux Kernel documentation for `USB ACM <http://www.kernel.org/doc/Documentation/usb/acm.txt>`_ and `USB Serial <http://www.kernel.org/doc/Documentation/usb/usb-serial.txt>`_
+* `USB Glossary of Terms <http://belcarra.com/usb_glossary.html>`_
+* ST documentation:
+    * Reference Manual `RM0008
+      <http://www.st.com/web/en/resource/technical/document/reference_manual/CD00171190.pdf>`_
+      (PDF), Chapter 23, "Universal serial bus full-speed device
+      interface"
+    * Programming Manual `PM0056
+      <http://www.st.com/st-web-ui/static/active/en/resource/technical/document/programming_manual/CD00228163.pdf>`_
+      (PDF; assembly language and register reference)