OpenCL clGetDeviceIDs() returns a wrong num_devices

* Environment

FPGA board: Arria 10 GX FPGA development kit(DKDEV10AX115SA)

OpenCL and Quartus version: 18.1 pro.

OS: Win10(64bit)

PC: Dell precision tower 7910 (with two CPU installed)

* Problem

This FPGA board is initialized and installed in the PC according: “AN 807: Configuring the Intel Arria 10 GX FPGA Development Kit for the Intel® FPGA SDK for OpenCL”.

I run two Intel Altera OpenCL examples on it: “exm_opencl_hello_world_x64_windows” runs well on emulator and FPGA, but “exm_opencl_vector_add_x64_windows”.

For “exm_opencl_hello_world_x64_windows”, both on emulator and on FPGA are ok.

For “exm_opencl_vector_add_x64_windows”, on emulator is ok, but on FPGA will be stopped by some errors. By debugging it, I found that clGetDeviceIDs() get the num_devices as 128 for platform “Intel(R) FPGA SDK for OpenCL(TM)”. In fact, I have only one Intel FPGA OpenCL board there. If it tries to use 128 devices, surely it will crash. (“exm_opencl_hello_world_x64_windows” is ok because it only uses the first device.)

If I force it to only use the first device by modifying some codes, the “exm_opencl_vector_add_x64_windows” runs well on FPGA. But this is not a thorough solution.

I try to list all the platforms and the first device of each platform as followed. Is there something wrong? How to solve the problem that the clGetDeviceIDs() return a wrong device number?

***

When running on FPGA:

(vector_add_fpga_output.txt)

Initializing OpenCL

num_platforms: 3

print out platform info from No. 1 upto No. 3

Platform number 1:

Platform Name: NVIDIA CUDA

Platform Profile: FULL_PROFILE

Platform Version: OpenCL 1.1 CUDA 6.5.14

Platform Vendor: NVIDIA Corporation

This platform has 1 device(s), and its 1st device is:

Querying device for info:

========================

CL_DEVICE_NAME = Quadro K5200

CL_DEVICE_VENDOR = NVIDIA Corporation

CL_DEVICE_VENDOR_ID = 4318

CL_DEVICE_VERSION = OpenCL 1.1 CUDA

CL_DRIVER_VERSION = 340.66

CL_DEVICE_ADDRESS_BITS = 32

CL_DEVICE_AVAILABLE = true

CL_DEVICE_ENDIAN_LITTLE = true

CL_DEVICE_GLOBAL_MEM_CACHE_SIZE = 196608

CL_DEVICE_GLOBAL_MEM_CACHELINE_SIZE = 128

CL_DEVICE_GLOBAL_MEM_SIZE = 0

CL_DEVICE_IMAGE_SUPPORT = true

CL_DEVICE_LOCAL_MEM_SIZE = 49151

CL_DEVICE_MAX_CLOCK_FREQUENCY = 771

CL_DEVICE_MAX_COMPUTE_UNITS = 12

CL_DEVICE_MAX_CONSTANT_ARGS = 9

CL_DEVICE_MAX_CONSTANT_BUFFER_SIZE = 65536

CL_DEVICE_MAX_WORK_ITEM_DIMENSIONS = 3

CL_DEVICE_MEM_BASE_ADDR_ALIGN = 4096

CL_DEVICE_MIN_DATA_TYPE_ALIGN_SIZE = 128

CL_DEVICE_PREFERRED_VECTOR_WIDTH_CHAR = 1

CL_DEVICE_PREFERRED_VECTOR_WIDTH_SHORT = 1

CL_DEVICE_PREFERRED_VECTOR_WIDTH_INT = 1

CL_DEVICE_PREFERRED_VECTOR_WIDTH_LONG = 1

CL_DEVICE_PREFERRED_VECTOR_WIDTH_FLOAT = 1

CL_DEVICE_PREFERRED_VECTOR_WIDTH_DOUBLE = 1

Command queue out of order? = true

Command queue profiling enabled? = true

Platform number 2:

Platform Name: Intel(R) FPGA SDK for OpenCL(TM)

Platform Profile: EMBEDDED_PROFILE

Platform Version: OpenCL 1.0 Intel(R) FPGA SDK for OpenCL(TM), Version 18.1

Platform Vendor: Intel(R) Corporation

This platform has 128 device(s), and its 1st device is:

Querying device for info:

========================

CL_DEVICE_NAME = a10gx : Arria 10 Reference Platform (acla10_ref0)

CL_DEVICE_VENDOR = Intel(R) Corporation

CL_DEVICE_VENDOR_ID = 4466

CL_DEVICE_VERSION = OpenCL 1.0 Intel(R) FPGA SDK for OpenCL(TM), Version 18.1

CL_DRIVER_VERSION = 18.1

CL_DEVICE_ADDRESS_BITS = 64

CL_DEVICE_AVAILABLE = true

CL_DEVICE_ENDIAN_LITTLE = true

CL_DEVICE_GLOBAL_MEM_CACHE_SIZE = 32768

CL_DEVICE_GLOBAL_MEM_CACHELINE_SIZE = 0

CL_DEVICE_GLOBAL_MEM_SIZE = 2147483648

CL_DEVICE_IMAGE_SUPPORT = false

CL_DEVICE_LOCAL_MEM_SIZE = 16384

CL_DEVICE_MAX_CLOCK_FREQUENCY = 1000

CL_DEVICE_MAX_COMPUTE_UNITS = 1

CL_DEVICE_MAX_CONSTANT_ARGS = 8

CL_DEVICE_MAX_CONSTANT_BUFFER_SIZE = 536870912

CL_DEVICE_MAX_WORK_ITEM_DIMENSIONS = 3

CL_DEVICE_MEM_BASE_ADDR_ALIGN = 8192

CL_DEVICE_MIN_DATA_TYPE_ALIGN_SIZE = 1024

CL_DEVICE_PREFERRED_VECTOR_WIDTH_CHAR = 4

CL_DEVICE_PREFERRED_VECTOR_WIDTH_SHORT = 2

CL_DEVICE_PREFERRED_VECTOR_WIDTH_INT = 1

CL_DEVICE_PREFERRED_VECTOR_WIDTH_LONG = 1

CL_DEVICE_PREFERRED_VECTOR_WIDTH_FLOAT = 1

CL_DEVICE_PREFERRED_VECTOR_WIDTH_DOUBLE = 0

Command queue out of order? = false

Command queue profiling enabled? = true

Platform number 3:

Platform Name: Intel(R) FPGA Emulation Platform for OpenCL(TM) (preview)

Platform Profile: EMBEDDED_PROFILE

Platform Version: OpenCL 1.0 Intel(R) FPGA SDK for OpenCL(TM), Version 18.1

Platform Vendor: Intel(R) Corporation

This platform has 1 device(s), and its 1st device is:

Querying device for info:

========================

CL_DEVICE_NAME = Intel(R) FPGA Emulation Device (preview)

...

Platform: Intel(R) FPGA SDK for OpenCL(TM)

Using 128 device(s)

a10gx : Arria 10 Reference Platform (acla10_ref0)

Using AOCX: vector_add.aocx

Launching for device 0 (1000000 elements)

Time: 183.631 ms

Kernel time (device 0): 174.791 ms

Verification: PASS