HLS pragmas and directives let you configure the synthesis results for your code.
- HLS Pragmas are added to the source code to enable the optimization or change in the original source code. Every time the code is synthesized, it is implemented according to the specified pragmas.
- HLS Optimization Directives can be specified as HLS configuration file commands that are associated with the HLS component. The config files can be reused across multiple HLS components, allowing you to customize the synthesis results for the same code base across different components.
Important: In some cases where pragmas
or directives conflict with other pragmas or directives, the synthesis process returns
an error until you resolve the conflict. However, in some cases the first pragma or
directive encountered takes precedence over the second pragma or directive, and the
second is ignored. This information should be reported in the log file or console
window.
To add pragmas or directives to your project:
- In the Vitis Component Explorer open a Source file of the HLS component by selecting it under the Sources folder.
- With the Source file opened, select the HLS Directive command (
) from the far right toolbar
menu of the Vitis unified IDE to open the
HLS Directive editor, as shown in the
following figure.Figure 1. HLS Directive Editor
- The HLS Directive
editor displays a hierarchy of the current source code and lets you add a directive
or pragma to the design; directives go into the config file and pragmas go into the
source file. In the preceding figure, the entry that is added to the config file is:
After selecting OK, you will see it added to the Config File editor.syn.directive.array_partition=dct_2d in_block factor=8 type=cyclic - Select the Add Directive command
from the HLS Directive
editor by selecting the function or loop or variable you want to add a directive to
and select the '+' on the right side as shown in the following figure.
Modify an existing directive by selecting the Edit Directive command next to the directive.