FIFO Intel® FPGA IP User Guide

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ID 683522
Date 7/08/2024
Public
Document Table of Contents
Document Table of Contents x
1. FIFO Intel® FPGA IP User Guide
1. FIFO Intel® FPGA IP User Guide x
1.1. Configuration Methods 1.2. Specifications 1.3. FIFO Functional Timing Requirements 1.4. SCFIFO ALMOST_EMPTY Functional Timing 1.5. FIFO Output Status Flag and Latency 1.6. FIFO Metastability Protection and Related Options 1.7. FIFO Synchronous Clear and Asynchronous Clear Effect 1.8. SCFIFO and DCFIFO Show-Ahead Mode 1.9. Different Input and Output Width 1.10. DCFIFO Timing Constraint Setting 1.11. Coding Example for Manual Instantiation 1.12. Design Example 1.13. Gray-Code Counter Transfer at the Clock Domain Crossing 1.14. Guidelines for Embedded Memory ECC Feature 1.15. FIFO Intel® FPGA IP User Guide Archives 1.16. Document Revision History for the FIFO Intel® FPGA IP User Guide
1.2. Specifications x
1.2.1. Verilog HDL Prototype 1.2.2. VHDL Component Declaration 1.2.3. VHDL LIBRARY-USE Declaration 1.2.4. FIFO Signals 1.2.5. FIFO Parameter Settings
1.7. FIFO Synchronous Clear and Asynchronous Clear Effect x
1.7.1. Recovery and Removal Timing Violation Warnings when Compiling a DCFIFO
1.10. DCFIFO Timing Constraint Setting x
1.10.1. Embedded Timing Constraint 1.10.2. User Configurable Timing Constraint
1.10.2. User Configurable Timing Constraint x
1.10.2.1. SDC Commands
1. FIFO Intel® FPGA IP User Guide

1.7.1. Recovery and Removal Timing Violation Warnings when Compiling a DCFIFO

During compilation of a design that contains a DCFIFO, the Quartus® Prime software may issue recovery and removal timing violation warnings.

You may safely ignore warnings that represent transfers from aclr to the read side clock domain. To ensure that the design meets timing, enable the ACLR synchronizer for both read and write domains.

To enable the ACLR synchronizer for both read and write domains, on the DCFIFO 2 tab of the FIFO Intel® FPGA IP core, turn on Asynchronous clear, Add circuit to synchronize ‘aclr’ input with ‘wrclk’, and Add circuit to synchronize ‘aclr’ input with ‘rdclk’.

Note: For correct timing analysis, Altera recommends enabling the Removal and Recovery Analysis option in the Timing Analyzer tool when you use the aclr signal. The analysis is turned on by default in the Timing Analyzer tool.

When the Add circuit to synchronize ‘aclr’ input with ‘wrclk’ and Add circuit to synchronize ‘aclr’ input with ‘rdclk’ options are enabled, you can apply the following false path assignment on the reset path:

  • set_false_path -to *dcfifo:dcfifo_component|dcfifo_*:auto_generated|dffpipe_*:wraclr|dffe*a[0]
  • set_false_path -to *dcfifo:dcfifo_component|dcfifo_*:auto_generated|dffpipe_*:rdaclr|dffe*a[0]

While the metastability issue is resolved by the circuit, the system design still requires a certain maximum delay even though it is asynchronous.

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