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

ID 683243
Date 10/04/2021
Public

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1.1.1.4. Launch and Latch Edges

All timing analysis requires the presence of one or more clock signals. The Timing Analyzer determines clock relationships for all register-to-register transfers in your design by analyzing the clock setup and hold relationship between the launch edge and latch edge of the clock.

The launch edge of the clock signal is the clock edge that sends data out of a register or other sequential element, and acts as a source for the data transfer. The latch edge is the active clock edge that captures data at the data port of a register or other sequential element, acting as a destination for the data transfer.

Figure 6. Setup and Hold Relationship for Launch and Latch Edges 10ns ApartIn this example, the launch edge sends the data from register reg1 at 0 ns, and the register reg2 captures the data when triggered by the latch edge at 10 ns. The data arrives at the destination register before the next latch edge.

You must define all clocks in your design by assigning a clock constraint to each clock source node. These clock constraints provide the structure required for repeatable data relationships. If you do not constrain the clocks in your design, the Intel® Quartus® Prime software analyzes all clocks as 1 GHz clocks to maximize timing based Fitter effort. To ensure realistic slack values, you must constrain all clocks in your design with real values.