Intel® Hyperflex™ Architecture High-Performance Design Handbook

ID 683353
Date 10/04/2021
Document Table of Contents Initial Conditions and Hyper-Registers

The Intel® Hyperflex™ architecture routing fabric includes Hyper-Registers throughout to achieve the highest performance. However, unless properly accounted for, initial power-up conditions can limit the Compiler's ability to retime registers into Hyper-Registers. Rather than relying on initial conditions, use a single reset signal to place the design in a known, functional state until all the interfaces have powered up, locked, and trained.

If you must rely on initial conditions, and your system requires that all registers start synchronously, the use of clock gating is recommended. Because Hyper-Registers lack a reset or enable signal, you cannot initialize them to a specific value using a reset control signal. Intel® Stratix® 10 Hyper-Registers can power up to 0 or 1. Intel® Agilex™ Hyper-Registers power up to 1 during configuration. When the system starts up, right after configuration, the initial values are present without the need for an explicit reset.

Clock Gating For ALM and Hyper-Registers

Independent signals drive the internal clock controls of ALM registers and Hyper-Registers in Intel® Hyperflex™ architecture FPGAs. During the configuration process, the registers become active row by row (as opposed to device wide). In addition, ALM register clocks can potentially enable independently from Hyper-Register clocks. If the design clock is free running, this can cause potential race conditions between rows and between ALM registers and Hyper-Registers. These conditions can result in potential overwrite of initial conditions. To avoid these scenarios, gate the clock until after all clock controlling logic de-asserts, and all registers are active.

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