Documentation: migrate "Auto-Mounter" from wiki

link: https://cwiki.apache.org/confluence/display/NUTTX/Auto-Mounter

Documentation/guides/automounter.rst

@@ -0,0 +1,69 @@
+============
+Auto-Mounter
+============
+
+General Description
+===================
+NuttX implements an auto-mounter than can make working with SD cards or other
+removable media easier. With the auto-mounter, the file system will be
+automatically mounted when media is inserted and automatically unmounted when
+the media is removed.
+
+The auto is enable by selecting in the NuttX configuration::
+
+  CONFIG_FS_AUTOMOUNTER=y
+
+
+WARNING: SD cards should never be removed without first unmounting them. This
+is to avoid data and possible corruption of the file system. Certainly this is
+the case if you are writing to the SD card at the time of the removal. If you
+use the SD card for read-only access, however, then I cannot think of any
+reason why removing the card without mounting would be harmful.
+
+For applications that write to the removable media, the automatic unmount is
+still beneficial (as opposed to leaving a broken mount in place) although
+should not be relied upon for a proper solution.
+
+Board-Specific Support
+======================
+
+Like many components of NuttX, the auto-mounter has a upper-half/lower-half
+architecture:
+
+* **Upper half** The upper half is the file ``fs/fs_automount.c``. This upper
+  half performs the basic automount activities. It responds to media
+  insertion and removal events by mounting and unmounting the file system on
+  the media. This includes logic to handle unmount retries: The unmount cannot
+  be performed while applications have open files on the media. In this case,
+  the auto-mounter will periodically retry the unmount until all of the
+  applications close there references to files on the non-existent media.
+
+* **Lower Half** The lower half is defined by a standard interface. That
+  interface definition is in the header file ``include/nuttx/fs/automount.h``.
+  The lower half interface provides: (1) mount information including file
+  system type, block driver path, and mount point path, (2) mount and unmount
+  retry delays, and (3) and callbacks to attach to and management the media
+  insertion / removal interrupts.
+
+Example Implementation
+======================
+
+There is an example implementation of this lower half interface at
+``boards/arm/sama5/sama5d4-ek/src/sam_automount.c``. The ``boards/arm/sama5/sama5d4-ek/Kconfig``
+as the board-specific configuration for the auto-mounter. You can see
+the configuration settings in the ``boards/arm/sama5/sama5d4-ek/configs/nsh/defconfig``
+and ``boards/arm/sama5/sama5d4-ek/configs/nxwm/defconfig`` configuration files::
+
+  CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT=y
+  CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_FSTYPE="vfat"
+  CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_BLKDEV="/dev/mmcsd0"
+  CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_MOUNTPOINT="/mnt/sdcard"
+  CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_DDELAY=1000
+  CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_UDELAY=2000
+
+These setting determine the values in the lower half interface. The interrupt is
+provided by a PIO pin defined in ``boards/arm/sama5/sama5d4-ek/src/sama5e4-ek.h`` and
+the implementation of the interface and callbacks is in
+``boards/arm/sama5/sama5d4-ek/src/sam_automount.c``.
+
+

Documentation/guides/index.rst

@@ -25,3 +25,4 @@ Guides
   gdbwithpython.rst
   ofloader.rst
   testingtcpip.rst
+  automounter.rst