Kernel Execution Modes - 2020.2 English

Vitis Unified Software Platform Documentation: Application Acceleration Development (UG1393)

Document ID

UG1393

Release Date

2021-03-22

Version

2020.2 English

There are three types of kernel execution modes, as described in the following table. These modes are mutually exclusive; each kernel can only operate in one of these modes. Kernels with different execution modes can be linked together by the Vitis linker to form the FPGA binary.

Tip: The table below provides a summary of the three execution modes. Refer to Supported Kernel Execution Models in the XRT documentation for additional details.

Table 1. Kernel Execution Modes
Sequential Mode	Pipelined Mode	Free-Running Mode
Control protocol: `ap_ctrl_hs` A kernel is started by the host application using an API call. Once the kernel is done, it notifies the host application. The kernel can only restart once current task is completed. Legacy mode for kernels using memory-based data transfers.	Control protocol: `ap_ctrl_chain` A kernel is started by the host application using an API call. Once the kernel is ready for new data, it notifies the host application. The kernel can be restarted before its current task is completed. Improves performance as multiple invocations of kernel can be overlapped. Default mode for kernels using memory-based data transfers.	Control protocol: `ap_ctrl_none` A kernel starts as soon as the device is programmed with the `xclbin`. A kernel is running continuously and synchronizes on availability of data. Free-running mode is not supported for kernels described in OpenCL C.