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

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ID 683243
Date 8/03/2023
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Document Table of Contents
Document Table of Contents x
1. Answers to Top FAQs 2. Timing Analysis Introduction 3. Using the Intel® Quartus® Prime Timing Analyzer A. Intel® Quartus® Prime Pro Edition User Guides
2. Timing Analysis Introduction x
2.1. What's New In This Version 2.2. Timing Analysis Basic Concepts 2.3. Timing Analysis Overview Document Revision History
2.2. Timing Analysis Basic Concepts x
2.2.1. Timing Path and Clock Analysis 2.2.2. Clock Setup Analysis 2.2.3. Clock Hold Analysis 2.2.4. Recovery and Removal Analysis 2.2.5. Multicycle Path Analysis 2.2.6. Metastability Analysis 2.2.7. Timing Pessimism 2.2.8. Clock-As-Data Analysis 2.2.9. Multicorner Timing Analysis 2.2.10. Time Borrowing
2.2.1. Timing Path and Clock Analysis x
2.2.1.1. The Timing Netlist 2.2.1.2. Timing Paths 2.2.1.3. Data and Clock Arrival Times 2.2.1.4. Launch and Latch Edges
2.2.5. Multicycle Path Analysis x
2.2.5.1. Multicycle Clock Hold 2.2.5.2. Multicycle Clock Setup
2.2.10. Time Borrowing x
2.2.10.1. Time Borrowing Limitations 2.2.10.2. Time Borrowing with Latches
3. Using the Intel® Quartus® Prime Timing Analyzer x
3.1. Timing Analysis Flow 3.2. Step 1: Specify Timing Analyzer Settings 3.3. Step 2: Specify Timing Constraints 3.4. Step 3: Run the Timing Analyzer 3.5. Step 4: Analyze Timing Reports 3.6. Applying Timing Constraints 3.7. Timing Analyzer Tcl Commands 3.8. Timing Analysis of Imported Compilation Results 3.9. Using the Intel® Quartus® Prime Timing Analyzer Document Revision History 3.10. Intel® Quartus® Prime Pro Edition User Guide: Timing Analyzer Archive
3.4. Step 3: Run the Timing Analyzer x
3.4.1. Setting the Operating Conditions for Timing Analysis 3.4.2. Enabling Time Borrowing Optimization 3.4.3. Promoting Critical Warnings to Errors
3.5. Step 4: Analyze Timing Reports x
3.5.1. Generating Timing Reports 3.5.2. Cross-Probing with Design Assistant 3.5.3. Launching Design Assistant from Timing Analyzer 3.5.4. Locating Timing Paths in Other Tools 3.5.5. Correlating Constraints to the Timing Report
3.5.1. Generating Timing Reports x
3.5.1.1. Report Fmax Summary 3.5.1.2. Report Timing 3.5.1.3. Report Timing By Source Files 3.5.1.4. Report Data Delay 3.5.1.5. Report Net Delay 3.5.1.6. Report Clocks and Clock Network 3.5.1.7. Report Clock Transfers 3.5.1.8. Report Metastability 3.5.1.9. Report CDC Viewer 3.5.1.10. Report Asynchronous CDC 3.5.1.11. Report Logic Depth 3.5.1.12. Report Neighbor Paths 3.5.1.13. Report Register Spread 3.5.1.14. Report Route Net of Interest 3.5.1.15. Report Retiming Restrictions 3.5.1.16. Report Register Statistics 3.5.1.17. Report Pipelining Information 3.5.1.18. Report Time Borrowing Data 3.5.1.19. Report Exceptions and Exceptions Reachability 3.5.1.20. Report Bottlenecks
3.5.1.13. Report Register Spread x
3.5.1.13.1. Registers with High Timing Path Endpoint Tension 3.5.1.13.2. Registers with High Immediate Fan-Out Tension
3.5.1.20. Report Bottlenecks x
3.5.1.20.1. Specifying Custom Bottleneck Criteria
3.5.2. Cross-Probing with Design Assistant x
3.5.2.1. Cross-Probing from Design Assistant to Timing Analyzer
3.6. Applying Timing Constraints x
3.6.1. Recommended Initial SDC Constraints 3.6.2. SDC File Precedence 3.6.3. Modifying Iterative Constraints 3.6.4. Using Entity-bound SDC Files 3.6.5. Creating Clocks and Clock Constraints 3.6.6. Creating I/O Constraints 3.6.7. Creating Delay and Skew Constraints 3.6.8. Creating Timing Exceptions 3.6.9. Using Fitter Overconstraints 3.6.10. Example Circuit and SDC File
3.6.1. Recommended Initial SDC Constraints x
3.6.1.1. Create Clock (create_clock) 3.6.1.2. Derive PLL Clocks (derive_pll_clocks) 3.6.1.3. Derive Clock Uncertainty (derive_clock_uncertainty) 3.6.1.4. Set Clock Groups (set_clock_groups)
3.6.4. Using Entity-bound SDC Files x
3.6.4.1. Entity-bound Constraint Scope 3.6.4.2. Entity-bound Constraint Examples
3.6.5. Creating Clocks and Clock Constraints x
3.6.5.1. Creating Base Clocks 3.6.5.2. Creating Virtual Clocks 3.6.5.3. Creating Generated Clocks (create_generated_clock) 3.6.5.4. Deriving PLL Clocks 3.6.5.5. Creating Clock Groups (set_clock_groups) 3.6.5.6. Accounting for Clock Effect Characteristics 3.6.5.7. Constraining CDC Paths
3.6.5.1. Creating Base Clocks x
3.6.5.1.1. Automatic Clock Detection and Constraint Creation
3.6.5.2. Creating Virtual Clocks x
3.6.5.2.1. Specifying I/O Interface Uncertainty 3.6.5.2.2. I/O Interface Clock Uncertainty Example
3.6.5.3. Creating Generated Clocks (create_generated_clock) x
3.6.5.3.1. Clock Divider Example (-divide_by) 3.6.5.3.2. Clock Multiplexer Example
3.6.5.5. Creating Clock Groups (set_clock_groups) x
3.6.5.5.1. Exclusive Clock Groups (-logically_exclusive or -physically_exclusive) 3.6.5.5.2. Asynchronous Clock Groups (-asynchronous) 3.6.5.5.3. set_clock_groups Constraint Tips
3.6.5.6. Accounting for Clock Effect Characteristics x
3.6.5.6.1. Set Clock Latency (set_clock_latency) 3.6.5.6.2. Clock Uncertainty
3.6.6. Creating I/O Constraints x
3.6.6.1. Input Constraints (set_input_delay) 3.6.6.2. Output Constraints (set_output_delay)
3.6.7. Creating Delay and Skew Constraints x
3.6.7.1. Advanced I/O Timing and Board Trace Model Delay 3.6.7.2. Maximum Skew (set_max_skew) 3.6.7.3. Net Delay (set_net_delay)
3.6.8. Creating Timing Exceptions x
3.6.8.1. Timing Exception Precedence 3.6.8.2. False Paths (set_false_path) 3.6.8.3. Minimum and Maximum Delays 3.6.8.4. Multicycle Paths 3.6.8.5. Multicycle Exception Examples 3.6.8.6. Delay Annotation 3.6.8.7. Constraining Design Partition Ports
3.6.8.4. Multicycle Paths x
3.6.8.4.1. Common Multicycle Applications 3.6.8.4.2. Relaxing Setup with Multicycle (set_multicyle_path) 3.6.8.4.3. Accounting for a Phase Shift (-phase)
3.6.8.5. Multicycle Exception Examples x
3.6.8.5.1. Default Multicycle Analysis 3.6.8.5.2. End Multicycle Setup = 2 and End Multicycle Hold = 0 3.6.8.5.3. End Multicycle Setup = 2 and End Multicycle Hold = 1 3.6.8.5.4. Same Frequency Clocks with Destination Clock Offset 3.6.8.5.5. Destination Clock Frequency is a Multiple of the Source Clock Frequency 3.6.8.5.6. Destination Clock Frequency is a Multiple of the Source Clock Frequency with an Offset 3.6.8.5.7. Source Clock Frequency is a Multiple of the Destination Clock Frequency 3.6.8.5.8. Source Clock Frequency is a Multiple of the Destination Clock Frequency with an Offset
3.7. Timing Analyzer Tcl Commands x
3.7.1. The quartus_sta Executable 3.7.2. Collection Commands
3.7.2. Collection Commands x
3.7.2.1. Wildcard Characters 3.7.2.2. Adding and Removing Collection Items 3.7.2.3. Query of Collections 3.7.2.4. Using the get_pins Command
1. Answers to Top FAQs
2. Timing Analysis Introduction
3. Using the Intel® Quartus® Prime Timing Analyzer
A. Intel® Quartus® Prime Pro Edition User Guides

3.5.5. Correlating Constraints to the Timing Report

Understanding how timing constraints and violations appear in the timing analysis reports is critical to understanding the results. The following examples show how specific constraints impact the timing analysis reports. Most timing constraints only affect the clock launch and latch edges. Specifically, create_clock and create_generated_clock create clocks with default relationships. However, the set_multicycle_path exception modifies the default setup and hold relationships. The set_max_delay and set_min_delay constraints are low-level overrides that explicitly indicate the maximum and minimum delays for the launch and latch edges.

The following figures show the results of running Report Timing on a particular path. You can view the incremental delays on the Data Path and Waveform tabs after running Report Timing. The Waveform tab allows you to visually reference the Data Path data, as well as the original .sdc constraints. You can use the Waveform tab to easily see how and where the constraints apply.

Figure 85. Report Timing (Waveform Tab)
In the following example, the design includes a clock driving the source and destination registers with a period of 10 ns. This results in a setup relationship of 10 ns (launch edge = 0 ns, latch edge = 10ns) and hold relationship of 0 ns (launch edge = 0 ns, latch edge = 0 ns) from the command: 
create_clock -name clocktwo -period 10.000 [get_ports {clk2}]
Figure 86. Setup Relationship 10ns
Figure 87. Hold Relationship 0ns
Adding set_multicycle_path constraints adds multicycles to relax the setup relationship, or open the window, making the setup relationship 20 ns while maintaining the hold relationship at 0 ns: 
set_multicycle_path -from clocktwo -to clocktwo -setup -end 2
set_multicycle_path -from clocktwo -to clocktwo -hold -end 1
Figure 88. Setup Relationship 20ns

Adding the following set_max_delay constraints explicitly overrides the setup relationship: 

set_max_delay -from [get_registers {regA}] -to \
     [get_registers {regB}] 15

Note that the only thing changing for these different constraints are the launch edge time and latch edge times for setup and hold analysis. Every other line item comes from delays inside the FPGA and are static for a given fit. View these reports to analyze how your constraints affect the timing reports.

Figure 89. Using set_max_delay

For I/O, you must add set_input_delay and set_output_delay constraints, as the following example shows. These constraints describe delays on signals from outside of the FPGA design that connect to the design's I/O ports. 

create_clock -period 10 [get_ports clk] 
# Clock used by the transfer, clock relationship is 10ns

# Setup constraints
set_output_delay -clock clk -max 1.2 [get_ports out] 
# Subtracted from Data Required Path as oExt
set_max_delay -from [get_registers B] 12 
# Sets latch edge time

# Hold constraints
set_output_delay -clock clk -min 2.3 [get_ports out] 
# Subtracted from Data Required Path as oExt
set_min_delay -from [get_registers B] 8 
# Sets latch edge time

The values of these constraints are the delays of the external signals between an external register and a port on the design. The -clock argument to the set_input_delay and set_output_delay specifies the clock domain that the external signal belongs to, or rather, the clock domain of the external register connected to the I/O port. The -min and -max options specify the worst-case or best-case delay; not specifying either option causes the worst- and best-case delays to be equal. I/O delays display as iExt or oExt in the Type column, as the following example reports shows.

Figure 90. Setup Slack Path Report and Waveforms for a Reg-To-Output Same-Clock Transfer
Figure 91. Hold Slack Path Report and Waveforms for a Reg-To-Output Same-Clock Transfer

A clock relationship, which is the difference between the launching and latching clock edge of a transfer, is determined by the clock waveform, multicycle constraints, and minimum and maximum delay constraints. The Timing Analyzer also adds the value of set_output_delay as an oExt value. For outputs, this value is part of the Data Required Path, since this is the external part of the analysis. The setup report subtracts the -max value, making the setup relationship harder to meet, since the Data Arrival Path delay must be shorter than the Data Required Path delay. The Timing Analyzer also subtracts the -min value. This subtraction is why a negative number causes more restrictive hold timing. The Data Arrival Path delay must be longer than the Data Required Path delay.

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