Intel® FPGA SDK for OpenCL™ Pro Edition: Programming Guide

ID 683846
Date 9/26/2022

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Document Table of Contents Declaring the Pipe Handle

Use the pipe variable to define the static pipe connectivity between kernels or between kernels and I/O.

To read from and write to a pipe, the kernel must pass the pipe variable to each of the corresponding API call.

Declare the pipe handle as a file scope variable in the kernel source code in the following convention: <access qualifier> pipe <type> <variable_name>

The <type> of the pipe may be any OpenCL™ built-in scalar or vector data type with a scalar size of 1024 bits or less. It may also be any user-defined type that is comprised of scalar or vector data type with a scalar size of 1024 bits or less.

Consider the following pipe handle declarations:

__kernel void first (pipe int c)

__kernel void second (write_only pipe int c)

The first example declares a read-only pipe handle of type int in the kernel first. The second example declares a write-only pipe in the kernel second. The kernel first may only read from pipe c, and the kernel second may only write to pipe c.

Important: The Intel® FPGA SDK for OpenCL™ Offline Compiler statically infers the connectivity of pipes in your system by matching the names of the pipe arguments. In the example above, the kernel first is connected to the kernel second by the pipe c.

In an Intel® OpenCL system, only one kernel may read to a pipe. Similarly, only one kernel may write to a pipe. If a non-I/O pipe does not have at least one corresponding reading operation and one writing operation, the offline compiler issues an error.

For more information in the Intel® FPGA SDK for OpenCL™ I/O pipe implementation, refer to Implementing I/O Pipes Using the io Attribute.