Intel® FPGA SDK for OpenCL™ Pro Edition: Getting Started Guide

ID 683188
Date 6/21/2022

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3.6.4. Emulating Your OpenCL Kernel

To emulate your OpenCL™ kernel, run the emulation .aocx file on the platform on which you built your kernel. The OpenCL Emulator uses a different OpenCL platform than when targeting FPGA hardware.

To emulate your kernel, perform the following steps:

To run the host application for emulation, invoke the env CL_CONFIG_CPU_EMULATE_DEVICES=<number_of_devices> <host_application_filename> command.
This command specifies the number of identical emulation devices that the Emulator needs to provide. By default, the emulator platform provides a single emulator device. Therefore, if your host code requires only a single device, you do not need to set the CL_CONFIG_CPU_EMULATE_DEVICES environment variable.

For the hello_world design example, run bin/host -emulator. The -emulator argument informs the host program to select the Intel® FPGA Emulation Platform for OpenCL.

Upon successful emulation of your kernel, you see the following output:

Using AOCX: hello_world.aocx

Kernel initialization is complete.

Launching the kernel...

Thread #2: Hello from Intel FPGA OpenCL Compiler!

Kernel execution is complete.
  • The emulator in Intel® FPGA SDK for OpenCL™ Pro Edition is built with GCC 7.2.0 as part of the offline compiler. When executing the host program for an emulated OpenCL device, the version of must be at least that of GCC 7.2.0. In other words, the LD_LIBRARY_PATH environment variable must ensure that the correct version of is found.

    If the correct version of is not found, the call to clGetPlatformIDs function fails to load the FPGA emulator platform and returns CL_PLATFORM_NOT_FOUND_KHR (error code -1001). Depending on which version of is found, the call to clGetPlatformIDs may succeed, but a later call to the clCreateContext function may fail with CL_DEVICE_NOT_AVAILABLE (error code -2).

    If LD_LIBRARY_PATH does not point to a sufficiently new, use the following syntax to invoke the host program:

    env LD_LIBRARY_PATH=<path to sufficiently new>:$LD_LIBRARY_PATH <host> [host arguments]
  • To enable debugging of kernel code, optimizations are disabled by default for the FPGA emulator. This can lead to sub-optimal execution speed when emulating kernel code.

    You can pass the -g0 flag to the aoc compile command to disable debugging and enable optimizations. This enables faster emulator execution.