Intel® High Level Synthesis Compiler Pro Edition: Reference Manual

ID 683349
Date 12/04/2023
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9.1. Effects of Specifying Target II and Target fMAX

Setting a target II (through hls_component_ii component attribute or #pragma ii loop pragma) and setting a target fMAX (through the hls_scheduler_target_fmax_mhz component attribute) affects how the scheduler in the Intel® HLS Compiler determines its efforts.

The following table summarizes the behavior of the scheduler in the Intel® HLS Compiler.

Set Target fMAX Set Target II Compiler Behavior
No Yes Best effort to achieve the II for the corresponding loop (may not achieve the best possible fMAX).
Yes No Best effort to achieve fMAX specified (may not achieve the best possible II).
Yes Yes Best effort to achieve the fMAX specified at the given II. The compiler errors out if it cannot achieve the requested II.
No No Use heuristic to achieve best fMAX/II trade-off.
Important: If you are using an fMAX target in the command line or a component attribute, specify #pragma ii for performance-critical loops in your design.