Knowledge Base Article
How do I interpret the terms "Estimated pairs recoverable by pairing ALUTs and registers as design grows" or "Estimated triples recoverable by pairing ALUTs and registers as design grows" in the Quartus II Fitter report?
Description
This is the Fitter's estimate of how many half-ALMs could be freed up by taking half-ALMs that only use the combinational ALUT part, and half-ALMs that only use the registers, and grouping them up so that each half-ALM uses both the Combinational ALUT and register resources. For each possible grouping, a half-ALM is recovered. Therefore, this quantity is shown as a negative number in the report. Using this quantity helps to estimate how much logic would be needed if the Fitter could pack all logic as densely as possible. Note that this type of packing may not give the optimal result for routability and timing performance. This information is used by the Quartus II software to calculate overall logic utilization percentage. See the related solution below for further information on logic utilization.