Intel® Quartus® Prime Pro Edition User Guide: Partial Reconfiguration

ID 683834
Date 1/11/2022

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2.7.6. Creating Freeze Logic for PR Regions

When partially reconfiguring a design, freeze all the outputs of each PR region to a known constant value. This freezing prevents the signal receivers in the static region from receiving undefined signals during the partial reconfiguration process.

The PR region cannot drive valid data until the partial reconfiguration process is complete, and the PR region is reset. Freezing is important for control signals that you drive from the PR region.

The freeze technique that you choose is optional, depending on the particular characteristics of your design. The freeze logic must reside in the static region of your design. A common freeze technique is to instantiate 2-to-1 multiplexers on each output of the PR region, to hold the output constant during partial reconfiguration.

Note: There is no requirement to freeze the global and non-global inputs of a PR region.
Figure 26. Freeze Technique #1

An alternative freeze technique is to register all outputs of the PR region in the static region. Then, use an enable signal to hold the output of these registers constant during partial reconfiguration.

Figure 27. Freeze Technique #2

The Partial Reconfiguration Region Controller IP core includes a freeze port for the region that it controls. Include this IP component with your system-level control logic to freeze the PR region output. For designs with multiple PR regions, instantiate one PR Region Controller IP core for each PR region in the design. The Intel® Quartus® Prime software includes the Avalon® Memory-Mapped Freeze Bridge and Avalon® Streaming Freeze Bridge Intel® FPGA IP cores. You can use these IP cores to implement freeze logic, or design your own freeze logic for these standard interface types.

The static region logic must be independent of all the outputs from the PR regions for a continuous operation. Control the outputs of the PR regions by adding the appropriate freeze logic for your design.