Intel® High Level Synthesis Compiler Pro Edition: Reference Manual

ID 683349
Date 12/19/2022

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2.4. Intel® HLS Compiler Hardware Model

The Intel® HLS Compiler attempts to pipeline functions as much as possible. Different stages of the pipeline might have multiple operations performed in parallel.

The following figure shows an example of the pipeline architecture generated by the Intel® HLS Compiler. The numbered operations on the right side represent the pipeline implementation of the C++ code on the left side of the figure. Each box in the right side of the figure is an operation in the pipeline.

Figure 1. Example of Pipeline Architecture

With a pipelined approach, multiple invocations of the component can be simultaneously active. For example, the earlier figure shows that the first invocation of the component can be returning a result at the same time the fourth invocation of the component is called.

One invocation of a component advances to the its next stage in the pipeline only after all of the operations of its current stage are complete.

Some operations can stall the pipeline. A common example of operations that can stall a pipeline is a variable latency operation like a memory load or store operation. To support pipeline stalls, the Intel® HLS Compiler propagates ready and valid signals through the pipeline to all operations that have a variable latency.

For operations that have a fixed latency, the Intel® HLS Compiler can statically schedule the interaction between the operations and ready signals are not needed between the stages with fixed latency operations. In these cases, the compiler optimizes the pipeline to statically schedule the operations, which significantly reduces the logic required to implement the pipeline.

For more details, refer to "FPGA Concepts" in Intel High Level Synthesis Compiler Pro Edition: Best Practices Guide .