Intel® Hyperflex™ Architecture High-Performance Design Handbook

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ID 683353
Date 10/04/2021
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2.4.2.7. Counters and Accumulators

Performance-limiting loops occur rarely in small, simple counters. Counters with unnatural rollover conditions (not a power of two), or irregular increments, are more likely to have a performance-limiting critical chain. When a performance-limiting loop occurs in a small counter (roughly 8 bits or less), write the counter as a fully decoded state machine, depending on all the inputs that control the counter. The counter still contains loops, but they are smaller, and not performance-limiting. When the counter is small (roughly 8 bits or less), the Fitter implements the counter in a single LAB. This implementation makes the counter fast because all the logic is placed close together.

You can also use loop unrolling to improve counter performance.

Figure 71. Counter and Accumulator LoopIn a counter and accumulator loop, a register's new value depends on its old value. This includes variants like LFSRs (linear feedback shift register) and gray code counters.

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