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, 80 insertions, 0 deletions

diff --git a/docs/source/libmaple/api/iwdg.rst b/docs/source/libmaple/api/iwdg.rst
new file mode 100644
index 0000000..65f9f7b
--- /dev/null
+++ b/docs/source/libmaple/api/iwdg.rst
@@ -0,0 +1,80 @@
+.. highlight:: c
+.. _libmaple-iwdg:
+
+``<libmaple/iwdg.h>``
+=====================
+
+Independent Watchdog (IWDG) support. The IWDG peripheral is common
+across supported targets, so everything documented here is portable.
+
+.. contents:: Contents
+   :local:
+
+Usage Note
+----------
+
+To use the independent watchdog, first call :ref:`iwdg_init()
+<libmaple-iwdg-iwdg_init>` with the appropriate prescaler and IWDG
+counter reload values for your application.  Afterwards, you must
+periodically call :ref:`iwdg_feed() <libmaple-iwdg-iwdg_feed>` before
+the IWDG counter reaches zero to reset the counter to its reload
+value.  If you do not, the chip will reset.
+
+Once started, the independent watchdog cannot be turned off.
+
+Devices
+-------
+
+None at this time.
+
+Functions
+---------
+
+.. _libmaple-iwdg-iwdg_init:
+.. doxygenfunction:: iwdg_init
+.. _libmaple-iwdg-iwdg_feed:
+.. doxygenfunction:: iwdg_feed
+
+Types
+-----
+
+.. doxygenenum:: iwdg_prescaler
+
+
+Register Maps
+-------------
+
+.. doxygendefine:: IWDG_BASE
+
+.. doxygenstruct:: iwdg_reg_map
+
+Register Bit Definitions
+------------------------
+
+These are given as source code.
+
+::
+
+    /* Key register */
+
+    #define IWDG_KR_UNLOCK                  0x5555
+    #define IWDG_KR_FEED                    0xAAAA
+    #define IWDG_KR_START                   0xCCCC
+
+    /* Prescaler register */
+
+    #define IWDG_PR_DIV_4                   0x0
+    #define IWDG_PR_DIV_8                   0x1
+    #define IWDG_PR_DIV_16                  0x2
+    #define IWDG_PR_DIV_32                  0x3
+    #define IWDG_PR_DIV_64                  0x4
+    #define IWDG_PR_DIV_128                 0x5
+    #define IWDG_PR_DIV_256                 0x6
+
+    /* Status register */
+
+    #define IWDG_SR_RVU_BIT                 1
+    #define IWDG_SR_PVU_BIT                 0
+
+    #define IWDG_SR_RVU                     (1U << IWDG_SR_RVU_BIT)
+    #define IWDG_SR_PVU                     (1U << IWDG_SR_PVU_BIT)