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The Importance of Timing Constraints in FPGA Designs

This blog post focuses on how to properly specify and validate timing constraints on a Lattice FPGA.

FAQ

Lattice Radiant: What are the Timing constraints for PMI_FIFO_DC using EBR IMPLIMENTATION?

Here are the constraints to be used:set_max_delay -from [get_pins -hierarchical */*wp_sync1_r*.ff_inst/Q] -to [get_pins -hierarchical */*wp_sync2_r*.ff_inst/DF] 2set_max_delay -from [get_pins -hierarchical */*rp_sync1_r*.ff_inst/Q] -to [get_pins -hierarchical */*rp_sync2_r*.ff_inst/DF]…

FAQ

Radiant: How are multiple lines of constraints handled in the device constraint editor?

Description:When handling multiple constraint commands in a constraint files, there might be confusion in which settings are applied. This FAQ will give examples on how device constraint editor handles it. See examples below for ldc_set_sysconfig below:   1. Usecase: Only one line for…

FAQ

Radiant and Diamond: HDL pin constraints not seen in Spreadsheet View/Device Constraint Editor

Description:In Lattice Radiant and Diamond, while using the Spreadsheet View/Device Constraint Editor, it is possible to not see the HDL pin constraints reflected in GUI.Solution:This may be because the pins mentioned in the lines of code have been optimized by the tool. See the following…

Blog

FPGA design constraints - performance and analysis to achieve design and timing closure

FAQ

Lattice iCECube2: Why does my Constraints for the output of Oscillators in iCECube2 is ignored by the tool?

Description:iCEcube2 only allows an inferred constraint on the internal OSC at its nominal value and Timing Analysis can't be set to a different frequency for the OSC as the user constraint will be ignored. Solution:This can work be around by feeding the output of the oscillator to a PLL (where the…

FAQ

Do BLOCK constraints limit the maximum coverage % reported in the timing report that can be achieved (<100%)?

The timing report generated by the Lattice Diamond Place and Route Tools report a timing coverage %. This number tells the user how complete their timing report is. Some customers require 100% timing coverage to ensure their designs are fully timed. In some cases the user cannot get 100% timing…

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Part Number Reference Guide

Get help with Lattice part numbers with our Part Number Reference Guide. Select a product family to view the part numbering system.

Document

iCEcube2 Timing Constraints

Application Note 1.0 PDF 0.8MB

Document

Timing Constraints Methodology for Source-Synchronous Interfaces

Application Note FPGA-AN-02078 1.0 PDF 0.9MB

Document

Lattice Radiant Timing Constraints Methodology

Application Note FPGA-AN-02059 1.5 PDF 1.9MB

Document

Lattice Radiant Constraints Propagation Engine

Application Note FPGA-AN-02097 1.0 PDF 0.6MB

FAQ

Radiant / Synplify Pro: Why does Postsyn reject the user's pre-synthesis constraints on an FDC file when Reveal Inserter is included in the project?

Description: The issue is caused by some differences in the behavior of the Verific and Synplify language parsers related to the handling of the escape characters in the instance name. Solution:This is not yet fixed by Synplify Pro and no timeline yet provided by the third-party tool.Currently,…

FAQ

Diamond: ERROR - par: I/O initial placement is unsuccessful. Check the I/O placement constraints / user preferences (such as pin locking) carefully

Description:When compiling a design on Diamond with multiple unassigned output ports, the below error might occur."ERROR - par: I/O initial placement is unsuccessful. Check the I/O placement constraints / user preferences (such as pin locking) carefully"This is due to users creating several unused…

FAQ

All FPGA: Why does PLL outputs' constraints does not propagate from ldc/fdc/sdc to Synthesis using both SynplifyPro & LSE?

Description:Lattice Diamond software does not use any pre-synthesis constraint file (SDC/LDC/FDC).Solution:There is a workaround to compensate for the limitation.Once the user has created any pre-synthesis constraint file, synthesize the design (for LSE) or synthesis + translate (for Synplify Pro).…

FAQ

Active-HDL: How to resolve unknowns (X) in timing simulation when the RTL simulation is fine and all constraints are met in Place and Route TRACE?

For post-route timing simulation, please set the SDF (Standard Delay Format) value and load as Maximal and Yes, respectively, in Aldec design settings.i.e.Step 1: In Aldec Active-HDL, select "Settings" from the Design menu. The Design Settings dialog box will be displayed. Expand the Simulation…

Document

Using Source Constraints in Lattice Devices with ispLEVER Software

Application Note AN8068 PDF 0.5MB

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Part Number Reference - MachXO3D Family

Get the part number description/reference guide for the MachXO3D family here.

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Part Number Reference - iCE40 Family

Get the part number description/reference guide for the iCE40 family here.

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Part Number Reference - ispCLOCK Family

Get the part number description/reference guide for the ispCLOCK family here.