Fixed and Unfixed Logic - 2021.2 English

Vivado Design Suite User Guide: Design Analysis and Closure Techniques (UG906)

Document ID
UG906
Release Date
2021-10-27
Version
2021.2 English

The Vivado tools track two different types of placement:

  • Elements placed by the user (shown in orange) are Fixed.
    • Fixed logic is stored in the XDC.
    • Fixed logic normally has a LOC constraint and might have a BEL constraint.
  • Elements placed by the tool (shown in blue) are Unfixed.

In the following figure, the I/O and Block RAM placement is Fixed. The slice logic is Unfixed.

Figure 1. Fixed and Unfixed Placement