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+The GObject Tango device
+========================
+
+UcaDevice is a generic Tango Device that wraps ``libuca`` in order to
+make libuca controlled cameras available as Tango devices.
+
+
+Architecture
+------------
+
+UcaDevice is derived from GObjectDevice and adds libuca specific features like
+start/stop recording etc.  The most important feature is *acquisition control*.
+UcaDevice is responsible for controlling acquisition of images from libuca. The
+last aquired image can be accessed by reading attribute ``SingleImage``.
+UcaDevice is most useful together with ImageDevice. If used together, UcaDevice
+sends each aquired image to ImageDevice, which in turn does configured
+post-processing like flipping, rotating or writing the image to disk.
+
+
+Attributes
+~~~~~~~~~~
+
+Besides the dynamic attributes translated from libuca properties
+UcaDevice has the following attributes:
+
+-  ``NumberOfImages (Tango::DevLong)``: how many images should be
+   acquired? A value of -1 means unlimited *(read/write)*
+-  ``ImageCounter (Tango::DevULong)``: current number of acquired images
+   *(read-only)*
+-  ``CameraName (Tango::DevString)``: name of libuca object type
+   *(read-only)*
+-  ``SingleImage (Tango::DevUChar)``: holds the last acquired image
+
+
+Acquisition Control
+~~~~~~~~~~~~~~~~~~~
+
+In UcaDevice acquisition control is mostly implemented by two
+``yat4tango::DeviceTasks``: *AcquisitionTask* and *GrabTask*.
+*GrabTask*'s only responsibility is to call ``grab`` on ``libuca``
+synchronously and post the data on to AcquisitionTask.
+
+*AcquisitionTask* is responsible for starting and stopping GrabTask and
+for passing image data on to ``ImageDevice`` (if exisiting) and to
+``UcaDevice`` for storage in attribute ``SingleImage``. It counts how
+many images have been acquired and checks this number against the
+configured ``NumberOfImages``. If the desired number is reached, it
+stops GrabTask, calls ``stop_recording`` on ``libuca`` and sets the
+Tango state to STANDBY.
+
+
+Plugins
+~~~~~~~
+
+As different cameras have different needs, plugins are used for special
+implementations. Plugins also makes UcaDevice and Tango Servers based on
+it more flexible and independent of libuca implementation.
+
+* PCO: The Pco plugin implements additional checks when writing ROI values.
+* Pylon: The Pylon plugin sets default values for ``roi-width`` and
+  ``roi-height`` from libuca properties ``roi-width-default`` and
+  ``roi-height-default``.
+
+
+Installation
+------------
+
+Detailed installation depends on the manifestation of UcaDevice. All
+manifestations depend on the following libraries:
+
+-  YAT
+-  YAT4Tango
+-  Tango
+-  GObjectDevice
+-  ImageDevice
+
+
+Build
+~~~~~
+
+::
+
+    export PKG_CONFIG_PATH=/usr/lib/pkgconfig
+    export PYLON_ROOT=/usr/pylon
+    export LD_LIBRARY_PATH=$PYLON_ROOT/lib64:$PYLON_ROOT/genicam/bin/Linux64_x64
+    git clone git@iss-repo:UcaDevice.git
+    cd UcaDevice
+    mkdir build
+    cd build
+    cmake ..
+    make
+
+
+Setup in Tango Database / Jive
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Before ``ds_UcaDevice`` can be started, it has to be registered manually
+in the Tango database. With ``Jive`` the following steps are necessary:
+
+1. Register Server Menu *Tools* → Server Wizard Server name → ds\_UcaDevice
+   Instance name → my\_server *(name can be chosen freely)* Next Cancel
+
+2.  Register Classes and Instances In tab *Server*: context menu on
+    ds\_UcaDevice → my\_server → Add Class Class: UcaDevice Devices:
+    ``iss/name1/name2`` Register server same for class ImageDevice
+
+3. Start server ::
+
+    export TANGO_HOST=anka-tango:100xx
+    export UCA_DEVICE_PLUGINS_DIR=/usr/lib(64)
+    ds_UcaDevice pco my_server
+
+4. Setup properties for UcaDevice context menu on device → Device wizard
+   Property StorageDevice: *address of previously registered ImageDevice
+   instance*
+
+5. Setup properties for ImageDevice context menu on device → Device wizard
+   PixelSize: how many bytes per pixel for the images of this camera?
+   GrabbingDevice: *address of previously registered UcaDevice instance*
+
+6. Finish restart ds_UcaDevice
+
+FAQ
+---
+
+*UcaDevice refuses to start up...?* Most likely there is no instance
+registered for class UcaDevice. Register an instance for this class and
+it should work.
+
+*Why does UcaDevice depend on ImageDevice?* UcaDevice pushes each new
+Frame to ImageDevice. Polling is not only less efficient but also prone
+to errors, e.g. missed/double frames and so on. Perhaps we could use the
+Tango-Event-System here!
+
+Open Questions, Missing Features etc.
+-------------------------------------
+
+* *Why do we need to specify ``Storage`` for UcaDevice and ``GrabbingDevice``
+  for ImageDevice?*
+
+  ImageDevice needs the Tango-Address of UcaDevice to mirror all Attributes and
+  Commands and to forward them to it. UcaDevice needs the Tango-Address of
+  ImageDevice to push a new frame on reception. A more convenient solution could
+  be using conventions for the device names, e.g. of the form
+  ``$prefix/$instance_name/uca`` and ``$prefix/$instance_name/image``.  That way
+  we could get rid of the two Device-Properties and an easier installation
+  without the process of registering the classes and instances in ``Jive``.
+
+* *Why does UcaDevice dynamically link to GObjectDevice?*
+
+  There is no good reason for it. Packaging and installing would be easier if we
+  linked statically to ``GObjectDevice`` because we would hide this dependency.
+  Having a separate ``GObjectDevice`` is generally a nice feature to make
+  ``GObjects`` available in Tango. However, there is currently no GObjectDevice
+  in use other than in the context of UcaDevice.
+
+* *Why must the plugin name be given as a command line parameter instead of a
+  Device-Property?*
+
+  There is no good reason for it. UcaDevice would be easier to use, if the
+  plugin was configured in the Tango database as a Device-Property for the
+  respective server instance.