LabVIEW 2013 FPGA IP Builder Help
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Directives are options you can apply to the algorithm VI to achieve certain timing performance or resource usage on FPGA. All directives are contained in a directives item that you can create for the algorithm VI. After you add the VI under the IP Builder project item, you can create a directives item for this VI in either of the following ways:
- Right-click the VI and select Create Directives from the shortcut menu.
- Right-click the IP Builder project item and select New»Directives from the shortcut menu. In the Select Top-Level VI dialog box that appears, select the VI for which you want to create directives and click OK.
LabVIEW adds a directives item, with the name VI filename directives, under the corresponding VI in the Project Explorer window. You can create multiple directive items for the VI.
After creating a directives item, you can right-click this item and select Properties from the shortcut menu to configure the directives item. Depending on the block diagram components of the top-level VI, you can configure the following directives:
- Top-level VI
- Interface of the top-level VI
||Note National Instruments recommends you configure these directives first.
- Loop structures
- Multiply functions
Configuring directives is an iterative process. After you configure the directives, estimate the performance and device utilization of the algorithm. If necessary, optimize the directive configurations until the estimated performance and device utilization meet the application requirements.
Flowchart for Configuring Directives
Use the following flowchart as a guideline to configure directives.
The previous flowchart involves the following steps:
- Specify an appropriate value for the Clock rate directive of the top-level VI.
- Specify appropriate values for the interface directives of the top-level VI.
- Check the algorithm VI for loop structures. If the algorithm VI does not contain loop structures or if the VI contains For Loops but the number of iteration counts of each For Loop is a fixed number less than or equal to 128, you can continue with the following step to configure the Initiation interval directive of the top-level VI. If the algorithm VI contains While Loops or if the VI contains For Loops and the number of iteration counts of each For Loop is greater than 128, configuring the Initiation interval directive of the top-level VI might not return the optimal performance. You can generate estimation reports first and then make optimization according to the reports.
- Specify an appropriate value for the Initiation interval directive of the top-level VI.
- Generate estimation reports.
- If the estimated initiation interval and latency are not acceptable, disable the Initiation interval directive of the top-level VI by removing the checkmark from the checkbox of this directive.
- In the estimation reports, identify the subVIs that fail to meet application requirements such as the initiation interval and latency, and configure the subVI directives properly.
||Note You can also refer to any warnings and suggestions in the Design Feedback report to optimize your IP design.
- In the estimation reports, identify the loop structures that fail to meet application requirements such as the initiation interval and latency, and configure the loop directives properly.
- If the estimated device utilization is not acceptable, configure the resource-related directives to optimize resource usage.
- Complete configuring the directives when the estimation reports meet all application requirements.