Asynchronous XRT (XRT Native API's)
===================================

This is simple example which showcases asynchronous programming mechanism through the user-defined queues.

**KEY CONCEPTS:** `XRT Native API <https://docs.xilinx.com/r/en-US/ug1393-vitis-application-acceleration/Setting-Up-XRT-Managed-Kernels-and-Kernel-Arguments>`__, `Asynchronous Programming <https://xilinx.github.io/XRT/2022.2/html/xrt_native_apis.html?highlight=queue#asynchornous-programming-with-xrt-experimental>`__

**KEYWORDS:** `xrt::queue <https://xilinx.github.io/XRT/2022.2/html/xrt_native_apis.html?highlight=queue#executing-multiple-tasks-through-queue>`__, `enqueue <https://xilinx.github.io/XRT/2022.2/html/xrt_native_apis.html?highlight=queue#executing-multiple-tasks-through-queue>`__, `wait() <https://xilinx.github.io/XRT/2022.2/html/xrt_native_apis.html?highlight=queue#executing-multiple-tasks-through-queue>`__


In this example we showcase asynchronous programming mechanism through the user-defined queues. The ``xrt::queue`` is lightweight, general-purpose queue implementation which is completely separated from core XRT native API data structures.

XRT queue implementation needs ``#include <experimental/xrt_queue.h`` to be added as the header file. The implementation also use C++17 features so the host code must be compiled with ``g++ -std=c++17``.

Executing multiple tasks through queue 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code:: c++
      :number-lines: 84
      
        
          xrt::queue main_queue;
          xrt::queue queue_bo1;
          auto bo0_event = main_queue.enqueue([&bo0] {bo0.sync(XCL_BO_SYNC_BO_TO_DEVICE); });
          auto bo1_event = queue_bo1.enqueue([&bo1] {bo1.sync(XCL_BO_SYNC_BO_TO_DEVICE); });
          main_queue.enqueue(bo1_event); 
          main_queue.enqueue([&run] {run.start(); run.wait(); });
          auto bo_out_event = main_queue.enqueue([&bo_out] {bo_out.sync(XCL_BO_SYNC_BO_FROM_DEVICE); });
          bo_out_event.wait();


In line number 86 and 87, ``bo0`` and ``bo1`` host-to-device data transfers are enqueued through two separate queues to achieve parallel transfers. To synchronize between these two queues, the returned event from the ``queue_bo1`` is enqueued in the ``main_queue``, similar to a task enqueue (line 88). As a result, any other task submitted after that event won't execute until the event is finished. So, in the above code example, subsequent task in the ``main_queue`` (such as kernel execution) would wait till the ``bo1_event`` is completed. By submitting an event returned from a ``queue::enqueue`` to another queue, we can synchronize among the queues.

**EXCLUDED PLATFORMS:** 

 - All NoDMA Platforms, i.e u50 nodma etc

DESIGN FILES
------------

Application code is located in the src directory. Accelerator binary files will be compiled to the xclbin directory. The xclbin directory is required by the Makefile and its contents will be filled during compilation. A listing of all the files in this example is shown below

::

   src/host.cpp
   src/vadd.cpp
   
Access these files in the github repo by `clicking here <https://github.com/Xilinx/Vitis_Accel_Examples/tree/master/host_xrt/asynchronous_xrt>`__.

COMMAND LINE ARGUMENTS
----------------------

Once the environment has been configured, the application can be executed by

::

   ./asynchronous_xrt -x <vadd XCLBIN>