Intel® Quartus® Prime Pro Edition User Guide: Timing Analyzer

ID 683243
Date 8/03/2023

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2.2.3. Clock Hold Analysis

To perform a clock hold check, the Timing Analyzer determines a hold relationship for each possible setup relationship that exists for all source and destination register pairs. The Timing Analyzer checks all adjacent clock edges from all setup relationships to determine the hold relationships.

The Timing Analyzer performs two hold checks for each setup relationship. The first hold check determines that the data launched by the current launch edge is not captured by the previous latch edge. The second hold check determines that the data launched by the next launch edge is not captured by the current latch edge. From the possible hold relationships, the Timing Analyzer selects the hold relationship that is the most restrictive. The most restrictive hold relationship is the hold relationship with the smallest difference between the latch and launch edges and determines the minimum allowable delay for the register-to-register path. In the following example, the Timing Analyzer selects hold check A2 as the most restrictive hold relationship of two setup relationships, setup A and setup B, and their respective hold checks.

Figure 11. Setup and Hold Check Relationships
Figure 12. Clock Hold Slack for Internal Register-to-Register Paths

The Timing Analyzer performs hold checks using the minimum delay when calculating data arrival time, and maximum delay when calculating data required time.

Figure 13. Clock Hold Slack Calculation from Input Port to Internal Register
Figure 14. Clock Hold Slack Calculation from Internal Register to Output Port