Why does the Fitter report a Segment Violation during post-route physical synthesis in the Quartus® Prime Pro Edition software version 25.3.1?

Description

Due to a problem in the Quartus® Prime Pro Edition Software version 25.3.1, the Fitter might unexpectedly terminate with a Segment Violation during Fitter Finalize for designs targeting Agilex® 7 FPGA M-Series devices.

The failure can occur after Hyper-Retimer operations complete, when Fitter Physical Synthesis (post-route physical synthesis / useful-skew optimization) begins. The issue is intermittent and can depend on the Fitter seed. Analysis and Synthesis and earlier Fitter stages may complete successfully before the crash.

Typical messages immediately before the failure include:

Info (18821): Fitter Hyper-Retimer operations ending 

Info (18258): Fitter Physical Synthesis operations beginning

The fatal error resembles:

*** Fatal Error: Segment Violation 
Module: quartus_fit CDB_ATOM_ITERM::is_connected

Resolution

To work around this problem in the Quartus® Prime Pro Edition Software version 25.3.1, follow these steps:

1. Open the Quartus project (.qpf) that fails during Fitter Finalize.

2. Add the following global assignment to the project Quartus Settings File (.qsf), or set the equivalent Assignment Editor option:

set_global_assignment -name POST_ROUTE_PHYSICAL_SYNTHESIS OFF

3. Recompile the design through the Fitter (or run a full compilation).

4. Open Compilation Report → Fitter → Ignored Assignments and confirm that POST_ROUTE_PHYSICAL_SYNTHESIS is not listed as ignored.

5. Compare timing results (worst-case slack / Fmax) against a successful compile that used the default post-route physical synthesis setting, because disabling this optimization can affect timing.

A software fix is not currently scheduled. Use the workaround above if you encounter this failure.