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

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ID 683068
Date 2/21/2024
Public
Document Table of Contents
Document Table of Contents x
1. Timing Analysis Introduction 2. Using the Intel® Quartus® Prime Timing Analyzer A. Intel® Quartus® Prime Standard Edition User Guides
1. Timing Analysis Introduction x
1.1. Timing Analysis Basic Concepts 1.2. Document Revision History
1.1. Timing Analysis Basic Concepts x
1.1.1. Timing Path and Clock Analysis 1.1.2. Clock Setup Analysis 1.1.3. Clock Hold Analysis 1.1.4. Recovery and Removal Analysis 1.1.5. Multicycle Path Analysis 1.1.6. Metastability Analysis 1.1.7. Timing Pessimism 1.1.8. Clock-As-Data Analysis 1.1.9. Multicorner Analysis
1.1.1. Timing Path and Clock Analysis x
1.1.1.1. The Timing Netlist 1.1.1.2. Timing Paths 1.1.1.3. Data and Clock Arrival Times 1.1.1.4. Launch and Latch Edges
1.1.5. Multicycle Path Analysis x
1.1.5.1. Multicycle Clock Hold 1.1.5.2. Multicycle Clock Setup
2. Using the Intel® Quartus® Prime Timing Analyzer x
2.1. Enhanced Timing Analysis for Intel® Arria® 10 Devices 2.2. Basic Timing Analysis Flow 2.3. Using Timing Constraints 2.4. Timing Analyzer Tcl Commands 2.5. Timing Analysis of Imported Compilation Results 2.6. Using the Intel® Quartus® Prime Timing Analyzer Document Revision History
2.2. Basic Timing Analysis Flow x
2.2.1. Step 1: Open a Project and Run the Fitter 2.2.2. Step 2: Specify Timing Constraints 2.2.3. Step 3: Specify General Timing Analyzer Settings 2.2.4. Step 4: Run Timing Analysis 2.2.5. Step 5: Analyze Timing Analysis Results
2.2.5. Step 5: Analyze Timing Analysis Results x
2.2.5.1. Timing Report Commands 2.2.5.2. Set Operating Conditions 2.2.5.3. Fmax Summary Report 2.2.5.4. Report Timing Command 2.2.5.5. Correlating Constraints to the Timing Report 2.2.5.6. Locating Timing Paths in Other Tools
2.3. Using Timing Constraints x
2.3.1. Recommended Initial SDC Constraints 2.3.2. SDC File Precedence 2.3.3. Iterative Constraint Modification 2.3.4. Creating Clocks and Clock Constraints 2.3.5. Creating I/O Constraints 2.3.6. Creating Delay and Skew Constraints 2.3.7. Creating Timing Exceptions 2.3.8. Example Circuit and SDC File
2.3.1. Recommended Initial SDC Constraints x
2.3.1.1. Create Clock (create_clock) 2.3.1.2. Derive PLL Clocks (derive_pll_clocks) 2.3.1.3. Derive Clock Uncertainty (derive_clock_uncertainty) 2.3.1.4. Set Clock Groups (set_clock_groups)
2.3.4. Creating Clocks and Clock Constraints x
2.3.4.1. Creating Base Clocks 2.3.4.2. Creating Virtual Clocks 2.3.4.3. Creating Generated Clocks (create_generated_clock) 2.3.4.4. Deriving PLL Clocks 2.3.4.5. Creating Clock Groups (set_clock_groups) 2.3.4.6. Accounting for Clock Effect Characteristics
2.3.4.1. Creating Base Clocks x
2.3.4.1.1. Automatic Clock Detection and Constraint Creation
2.3.4.2. Creating Virtual Clocks x
2.3.4.2.1. Specifying I/O Interface Uncertainty 2.3.4.2.2. I/O Interface Clock Uncertainty Example
2.3.4.3. Creating Generated Clocks (create_generated_clock) x
2.3.4.3.1. Clock Divider Example (-divide_by) 2.3.4.3.2. Clock Multiplexor Example
2.3.4.5. Creating Clock Groups (set_clock_groups) x
2.3.4.5.1. Exclusive Clock Groups (-exclusive) 2.3.4.5.2. Asynchronous Clock Groups (-asynchronous) 2.3.4.5.3. set_clock_groups Constraint Tips
2.3.4.6. Accounting for Clock Effect Characteristics x
2.3.4.6.1. Set Clock Latency (set_clock_latency) 2.3.4.6.2. Clock Uncertainty
2.3.5. Creating I/O Constraints x
2.3.5.1. Input Constraints (set_input_delay) 2.3.5.2. Output Constraints (set_output_delay)
2.3.6. Creating Delay and Skew Constraints x
2.3.6.1. Advanced I/O Timing and Board Trace Model Delay 2.3.6.2. Maximum Skew (set_max_skew) 2.3.6.3. Net Delay (set_net_delay) 2.3.6.4. Create Timing Netlist
2.3.7. Creating Timing Exceptions x
2.3.7.1. Timing Constraint Precedence 2.3.7.2. False Paths (set_false_path) 2.3.7.3. Minimum and Maximum Delays 2.3.7.4. Multicycle Paths 2.3.7.5. Multicycle Exception Examples 2.3.7.6. Delay Annotation
2.3.7.4. Multicycle Paths x
2.3.7.4.1. Common Multicycle Applications 2.3.7.4.2. Relaxing Setup with Multicycle (set_multicyle_path) 2.3.7.4.3. Accounting for a Phase Shift (-phase)
2.3.7.5. Multicycle Exception Examples x
2.3.7.5.1. Default Multicycle Analysis 2.3.7.5.2. End Multicycle Setup = 2 and End Multicycle Hold = 0 2.3.7.5.3. End Multicycle Setup = 2 and End Multicycle Hold = 1 2.3.7.5.4. Same Frequency Clocks with Destination Clock Offset 2.3.7.5.5. Destination Clock Frequency is a Multiple of the Source Clock Frequency 2.3.7.5.6. Destination Clock Frequency is a Multiple of the Source Clock Frequency with an Offset 2.3.7.5.7. Source Clock Frequency is a Multiple of the Destination Clock Frequency 2.3.7.5.8. Source Clock Frequency is a Multiple of the Destination Clock Frequency with an Offset
2.4. Timing Analyzer Tcl Commands x
2.4.1. The quartus_sta Executable 2.4.2. Collection Commands 2.4.3. Identifying the Intel® Quartus® Prime Software Executable from the SDC File
2.4.2. Collection Commands x
2.4.2.1. Wildcard Characters 2.4.2.2. Adding and Removing Collection Items 2.4.2.3. Query of Collections 2.4.2.4. Using the get_pins Command
1. Timing Analysis Introduction
2. Using the Intel® Quartus® Prime Timing Analyzer
A. Intel® Quartus® Prime Standard Edition User Guides

2.3.4.3. Creating Generated Clocks (create_generated_clock)

The Create Generate Clock (create_generated_clock) constraint allows you to define the properties and constraints of an internally generated clock in the design. You specify the Clock name (-name), the Source node (-source) from which clock derives, and the Relationship to the source properties. Define generated clocks for any node that modifies the properties of a clock signal, including modifying the phase, frequency, offset, or duty cycle.

You apply generated clocks most commonly on the outputs of PLLs, on register clock dividers, clock muxes, and clocks forwarded to other devices from an FPGA output port, such as source synchronous and memory interfaces. In the .sdc file, enter generated clocks after the base clocks definitions. Generated clocks automatically account for all clock delays and clock latency to the generated clock target.

The -source option specifies the name of a node in the clock path that you use as reference for your generated clock. The source of the generated clock must be a node in your design netlist, and not the name of a clock you previously define. You can use any node name on the clock path between the input clock pin of the target of the generated clock and the target node of its reference clock as the source node.

Specify the input clock pin of the target node as the source of your new generated clock. The source of the generated clock decouples from the naming and hierarchy of the clock source. If you change the clock source, you do not have to edit the generated clock constraint.

If you have multiple base clocks feeding a node that is the source for a generated clock, you must define multiple generated clocks. You associate each generated clock with one base clock using the -master_clock option in each generated clock statement. In some cases, generated clocks generate with combinational logic.

Depending on how your clock-modifying logic synthesizes, the signal name can change from one compilation to the next. If the name changes after you write the generated clock constraint, the Compiler ignores the generated clock because that target name no longer exists in the design. To avoid this problem, use a synthesis attribute or synthesis assignment to retain the final combinational node name of the clock-modifying logic. Then use the kept name in your generated clock constraint.

Figure 46. Example of clock-as-data

When you create a generated clock on a node that ultimately feeds the data input of a register, this creates a special case of “clock-as-data." The Timing Analyzer treats clock-as-data differently. For example, if you use clock-as-data with DDR, you must consider both the rise and the fall of this clock, and the Timing Analyzer reports both rise and fall. With clock-as-data, the Compiler treats the From Node as the target of the generated clock, and the Launch Clock as the generated clock.

In Example of Clock as Data, the first path is from toggle_clk (INVERTED) to clk, and the second path is from toggle_clk to clk. The slack in both cases is slightly different due to the difference in rise and fall times along the path. The Data Delay column reports the ~5 ps difference. Only the path with the lowest slack value requires consideration. The Timing Analyzer only reports the worst-case path between the two (rise and fall). In this example, if you do not define the generated clock on the register output, then timing analysis reports only one path with the lowest slack value.

You can use the derive_pll_clocks command to automatically generate clocks for all PLL clock outputs. The properties of the generated clocks on the PLL outputs match the properties you define for the PLL.


Section Content
Clock Divider Example (-divide_by)
Clock Multiplexor Example

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