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

ID 683068
Date 2/21/2024
Document Table of Contents Multicycle Paths

By default, the Timing Analyzer performs a single-cycle analysis, which is the most restrictive type of analysis. When analyzing a path without a multicycle constraint, the Timing Analyzer determines the setup launch and latch edge times by identifying the closest two active edges in the respective waveforms.
Figure 58. Default Setup and Hold Relationship (No Multicycle)

For hold time analysis, the timing analyzer analyzes the path for two timing conditions for every possible setup relationship, not just the worst-case setup relationship. Therefore, the hold launch and latch times can be unrelated to the setup launch and latch edges. The Timing Analyzer does not report negative setup or hold relationships. When the Timing Analyzer detects either a negative setup or a negative hold relationship, the Timing Analyzer moves both the launch and latch edges until the setup and hold relationship becomes positive.

A multicycle constraint adjusts this default setup or hold relationship by the number of clock cycles you specify, based on the source (-start) or destination (-end) clock. A setup multicycle constraint of 2 extends the worst-case setup latch edge by one destination clock period. If you do not specify -start and -end values, the default constraint is -end.

Figure 59. Setup and Hold Relationship with Multicycle = 2

Hold multicycle constraints derive from the default hold position (the default value is 0). An end hold multicycle constraint of 1 effectively subtracts one destination clock period from the default hold latch edge.

When the objects are timing nodes, the multicycle constraint only applies to the path between the two nodes. When an object is a clock, the multicycle constraint applies to all paths where the source node (-from) or destination node (-to) is clocked by the clock. When you adjust a setup relationship with a multicycle constraint, the hold relationship adjusts automatically.

You can use timing constraints to modify either the launch or latch edge times that the Timing Analyzer uses to determine a setup relationship or hold relationship.

Table 14.  Multicycle Constraints
Command Modification
set_multicycle_path -setup -end <value> Latch edge time of the setup relationship.
set_multicycle_path -setup -start<value> Launch edge time of the setup relationship.
set_multicycle_path -hold -end <value> Latch edge time of the hold relationship.
set_multicycle_path -hold -start <value> Launch edge time of the hold relationship.