Article ID: 000085888 Content Type: Troubleshooting Last Reviewed: 09/11/2012

Why is ALUT usage not the same in the "Fitter Resource Usage Summary" and "Fitter Resource Utilization by Entity" reports?

Environment

BUILT IN - ARTICLE INTRO SECOND COMPONENT
Description

In Stratix® II and Stratix III devices, each LAB is composed of ALMs, and each ALM can usually implement 2 ALUTs.  However, in some cases, only one of the ALUTs can be used, making the other one unavailable. Unavailable means that the ALUT is not currently implementing any logic for the design, but it is not available to be used.

The number of ALUTs Used reported in the Quartus® II Fitter Resource Usage Summary is the number of ALUTs that are used to implement logic in the design. This report does not include unavailable ALUTs; unavailable ALUTs are reported separately.

The number of Combinational ALUTs reported in the the Quartus II Fitter Utilization by Entity includes unavailable ALUTs in the total. This number equals the sum of the used ALUTs and the unavailable ALUTs reported in the Fitter Resource Usage Summary. 

Related Products

This article applies to 1 products

Stratix® II FPGAs

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