merge libmaple docs ("leaflabs-docs") into ./docs

In the past, libample documentation was forked out of this repository
because the documentation had increased in scope. For the librambutan,
and the rambutan project in general, we will try to keep documentation
closer to the source code, so the librambutan-specific documentation
should live here. Other sections of leaflabs-docs will be culled in a
following commit.

This merge attempts to maintain history by using a subtree strategy.
Followed directions at:

    http://nuclearsquid.com/writings/subtree-merging-and-you/

Full history for files should be accessible using the "--follow" flag to
git log, eg:

    git log --follow docs/source/adc.rst

It should be possible to pull patches from leaflabs-docs with:

    git pull -s subtree leaflabs-docs master

... at least until the docs in this repository diverge significantly.

1 files changed, 81 insertions, 0 deletions

diff --git a/docs/source/jtag.rst b/docs/source/jtag.rst
new file mode 100644
index 0000000..caba223
--- /dev/null
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@@ -0,0 +1,81 @@
+.. highlight:: cpp
+
+.. _jtag:
+
+JTAG
+====
+
+.. FIXME [0.1.0] Updated adapter schematic, better information
+
+JTAG is an interface for low-level debugging of digital devices. It
+gives instruction by instruction control over the microprocessor and
+allows data to be read and written to arbitrary memory and register
+locations. It is typically used with a debugging tool like `gdb
+<http://www.gnu.org/software/gdb/>`_ when hacking low level routines
+and hardware peripherals (we use it when working on :ref:`libmaple
+<libmaple>`) or to flash a new bootloader.
+
+Note that the STM32 on the Maple has a built-in low level serial
+debugger which could also be used to flash bootloaders, and
+:ref:`lang-assert` allows basic debugging over a USART serial channel.
+We expect only fairly advanced users to use this feature.
+
+.. contents:: Contents
+   :local:
+
+Wiring Diagram
+--------------
+
+.. figure:: /_static/img/jtag-wiring.png
+   :align: center
+   :alt: JTAG wiring diagram
+   :width: 7.4in
+   :target: _images/jtag-wiring.png
+
+   JTAG wiring diagram (`large version <_images/jtag-wiring.png>`_)
+   to connect a standard 20-pin ARM JTAG device to the 8-pin JTAG port
+   on the Maple.
+
+The Maple has holes for a 8-pin JTAG header, but that header is not
+soldered on.  To use JTAG, simply solder on standard 0.1" pitch male
+header pins (either the exact 4 by 2 block, or two 4-pin pieces of
+straight breakaway header).
+
+Compatible Devices
+------------------
+
+We have had good experience with the `Olimex ARM-USB-OCD
+<http://www.olimex.com/dev/arm-usb-ocd.html>`_ device, which costs
+about €55 plus shipping (as of April 2011).
+
+Function Reference
+------------------
+
+You can disable or enable the JTAG and Serial Wire debugging ports in
+software using the ``disableDebugPorts()`` and ``enableDebugPorts()``
+functions.
+
+* :ref:`lang-disabledebugports`
+* :ref:`lang-enabledebugports`
+
+Recommended Reading
+-------------------
+
+* `Wikipedia Article on Joint Test Action Group (JTAG)
+  <http://en.wikipedia.org/wiki/Joint_Test_Action_Group>`_
+
+* `STM32, GDB, OpenOCD How To
+  <http://fun-tech.se/stm32/OpenOCD/gdb.php>`_
+
+* `LeafLabs Wiki JTAG How To
+  <http://wiki.leaflabs.com/index.php?title=Maple_JTAG_How_To>`_
+
+* `LeafLabs forum thread on JTAG
+  <http://forums.leaflabs.com/topic.php?id=536>`_
+
+* ST documentation:
+
+  * Reference Manual `RM0008
+    <http://www.st.com/stonline/products/literature/rm/13902.pdf>`_
+    (PDF), Chapter 31, "Debug support", and Chapter 9,
+    "General-purpose and alternate function I/Os".