opencv/modules/gpu/doc/initalization_and_information.rst

Initalization and Information
=============================
.. highlight:: cpp

.. index:: gpu::getCudaEnabledDeviceCount

gpu::getCudaEnabledDeviceCount
----------------------------------

.. ocv:function:: int gpu::getCudaEnabledDeviceCount()

    Returns the number of installed CUDA-enabled devices. Use this function before any other GPU functions calls. If OpenCV is compiled without GPU support, this function returns 0.

.. index:: gpu::setDevice

gpu::setDevice
------------------
.. ocv:function:: void gpu::setDevice(int device)

    Sets a device and initializes it for the current thread. If the call of this function is omitted, a default device is initialized at the fist GPU usage.

    :param device: System index of a GPU device starting with 0.

.. index:: gpu::getDevice

gpu::getDevice
------------------
.. ocv:function:: int gpu::getDevice()

    Returns the current device index set by ``{gpu::getDevice}`` or initialized by default.

.. index:: gpu::GpuFeature

gpu::GpuFeature
---------------
.. ocv:class:: gpu::GpuFeature
    
Class providing GPU computing features. 
::

    enum GpuFeature
    {
        COMPUTE_10, COMPUTE_11,
        COMPUTE_12, COMPUTE_13,
        COMPUTE_20, COMPUTE_21,
        ATOMICS, NATIVE_DOUBLE
    };


.. index:: gpu::DeviceInfo

gpu::DeviceInfo
---------------
.. ocv:class:: gpu::DeviceInfo

Class providing functionality for querying the specified GPU properties. 
::

    class CV_EXPORTS DeviceInfo
    {
    public:
        DeviceInfo();
        DeviceInfo(int device_id);

        string name() const;

        int majorVersion() const;
        int minorVersion() const;

        int multiProcessorCount() const;

        size_t freeMemory() const;
        size_t totalMemory() const;

        bool supports(GpuFeature feature) const;
        bool isCompatible() const;
    };


.. index:: gpu::DeviceInfo::DeviceInfo
.. Comment: two lines below look like a bug

gpu::DeviceInfo::DeviceInfo
------------------------------- 
.. ocv:function:: gpu::DeviceInfo::DeviceInfo()

.. ocv:function:: gpu::DeviceInfo::DeviceInfo(int device_id)

    Constructs the ``DeviceInfo`` object for the specified device. If ``device_id`` parameter is missed, it constructs an object for the current device.

    :param device_id: System index of the GPU device starting with 0.

.. index:: gpu::DeviceInfo::name

gpu::DeviceInfo::name
-------------------------
.. ocv:function:: string gpu::DeviceInfo::name()

    Returns the device name.

.. index:: gpu::DeviceInfo::majorVersion

gpu::DeviceInfo::majorVersion
---------------------------------
.. ocv:function:: int gpu::DeviceInfo::majorVersion()

    Returns the major compute capability version.

.. index:: gpu::DeviceInfo::minorVersion

gpu::DeviceInfo::minorVersion
---------------------------------
.. ocv:function:: int gpu::DeviceInfo::minorVersion()

    Returns the minor compute capability version.

.. index:: gpu::DeviceInfo::multiProcessorCount

gpu::DeviceInfo::multiProcessorCount
----------------------------------------
.. ocv:function:: int gpu::DeviceInfo::multiProcessorCount()

    Returns the number of streaming multiprocessors.

.. index:: gpu::DeviceInfo::freeMemory

gpu::DeviceInfo::freeMemory
-------------------------------
.. ocv:function:: size_t gpu::DeviceInfo::freeMemory()

    Returns the amount of free memory in bytes.

.. index:: gpu::DeviceInfo::totalMemory

gpu::DeviceInfo::totalMemory
--------------------------------
.. ocv:function:: size_t gpu::DeviceInfo::totalMemory()

    Returns the amount of total memory in bytes.

.. index:: gpu::DeviceInfo::supports

gpu::DeviceInfo::supports
-----------------------------
.. ocv:function:: bool gpu::DeviceInfo::supports(GpuFeature feature)

    Provides information on GPU feature support. This function returns true if the device has the specified GPU feature. Otherwise, it returns false.

    :param feature: Feature to be checked. See :ocv:class:`gpu::GpuFeature`.

.. index:: gpu::DeviceInfo::isCompatible

gpu::DeviceInfo::isCompatible
---------------------------------
.. ocv:function:: bool gpu::DeviceInfo::isCompatible()

    Checks the GPU module and device compatibility. This function returns ``true`` if the GPU module can be run on the specified device. Otherwise, it returns false.

.. index:: gpu::TargetArchs

gpu::TargetArchs
----------------
.. ocv:class:: gpu::TargetArchs

Class providing a set of static methods to check what NVIDIA* card architecture the GPU module was built for.

The following method checks whether the module was built with the support of the given feature:

    .. ocv:function:: static bool gpu::TargetArchs::builtWith(GpuFeature feature)

        :param feature: Feature to be checked. See :ocv:class:`gpu::GpuFeature`.

There is a set of methods to check whether the module contains intermediate (PTX) or binary GPU code for the given architecture(s):

    .. ocv:function:: static bool gpu::TargetArchs::has(int major, int minor)

    .. ocv:function:: static bool gpu::TargetArchs::hasPtx(int major, int minor)

    .. ocv:function:: static bool gpu::TargetArchs::hasBin(int major, int minor)

    .. ocv:function:: static bool gpu::TargetArchs::hasEqualOrLessPtx(int major, int minor)

    .. ocv:function:: static bool gpu::TargetArchs::hasEqualOrGreater(int major, int minor)

    .. ocv:function:: static bool gpu::TargetArchs::hasEqualOrGreaterPtx(int major, int minor)

    .. ocv:function:: static bool gpu::TargetArchs::hasEqualOrGreaterBin(int major, int minor)

        :param major: Major compute capability version.

        :param minor: Minor compute capability version.

According to the CUDA C Programming Guide Version 3.2: "PTX code produced for some specific compute capability can always be compiled to binary code of greater or equal compute capability".