AN 917: Reset Design Techniques for Hyperflex® Architecture FPGAs

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ID 683539
Date 7/07/2025
Public
Document Table of Contents
Document Table of Contents x
1. AN 917: Reset Design Techniques for Hyperflex® Architecture FPGAs
1. AN 917: Reset Design Techniques for Hyperflex® Architecture FPGAs x
1.1. General Reset Recommendations 1.2. Reset Design Strategies 1.3. Analyzing Resets with Design Assistant 1.4. Implementing Reset Circuitry 1.5. Document Revision History for AN 917: Reset Design Techniques for Hyperflex® Architecture FPGAs
1.1. General Reset Recommendations x
1.1.1. Limit Reset Usage 1.1.2. Hyper-Registers Require Synchronous Reset
1.2. Reset Design Strategies x
1.2.1. Asynchronous Reset Design Strategies 1.2.2. Synchronous Reset Design Strategies
1.2.1. Asynchronous Reset Design Strategies x
1.2.1.1. Recovery and Removal Checks
1.3. Analyzing Resets with Design Assistant x
1.3.1. Example: Asynchronous Reset Design Assistant Analysis 1.3.2. Example: Synchronous Reset Design Assistant Analysis
1.3.1. Example: Asynchronous Reset Design Assistant Analysis x
1.3.1.1. Adding SDC Constraints to Asynchronous Reset Circuitry
1.4. Implementing Reset Circuitry x
1.4.1. Reset Coding Techniques 1.4.2. Avoiding Common Reset Coding Issues 1.4.3. Generating Synchronous Reset Trees 1.4.4. Reset Removal on Multi Clock Domain Designs 1.4.5. Using the Reset Release IP 1.4.6. Adding Clock Cycles to the Reset Sequence
1.4.1. Reset Coding Techniques x
1.4.1.1. Converting to Synchronous Resets
1.4.2. Avoiding Common Reset Coding Issues x
1.4.2.1. Coding Synchronous Reset with Follower Registers 1.4.2.2. Coding Reset-Related Optimizations
1.4.3. Generating Synchronous Reset Trees x
1.4.3.1. Reset Distribution through Hyper-Pipelining and Hyper-Retiming 1.4.3.2. Adding Pipeline Registers and Automatic Register Duplication
1.4.6. Adding Clock Cycles to the Reset Sequence x
1.4.6.1. C-Cycle Equivalence 1.4.6.2. Determining the Reset Sequence Requirement
1. AN 917: Reset Design Techniques for Hyperflex® Architecture FPGAs

1.4.1.1. Converting to Synchronous Resets

Complete the coding of your design before targeting an Hyperflex® architecture device. If you are using asynchronous resets in your design, convert them to synchronous resets to benefit from Hyper-Retiming performance optimization. Hyper-Retiming helps to meet the timing requirements for fast running clocks. The design blocks that are running slow clocks, and are already passing timing requirements, can continue using asynchronous resets.

Switching your code to use synchronous resets is simple, as the following example shows: 
//Asynchronous reset on control register
always @(posedge clk or negedge rstb)
	begin
		if (!rstb)
			control <= ‘d0;
		else
			control <= new_value;
	end

//Synchronous reset on control register
always @(posedge clk)
	begin
		if (!rstb)
			control <= ‘d0;
		else
			control <= new_value;
	end
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