Why does the fitter error happen with the message of can't read "rx1_clkout_H" while running a parallel loopback with the external VCXO design example of the GTS SDI IP generated by a former Quartus® version than 25.3?

Description

Due to some changes in the Quartus® Prime Pro Edition software version 25.3, you may see the following error while running a parallel loopback with an external VCXO design example of the GTS SDI IP generated by a former Quartus version other than 25.3. 

• Error: can't read "rx1_clkout_H": no such variable 

This problem occurs because some pfd.sdc paths have changed in the Quartus® Prime Pro Edition Software version 25.3. 

Resolution

To work around this problem during design migration from the former Quartus® Prime Pro Edition software version to version 25.3, modify the pfd.sdc file located in rtl/loopback/pfd/ directory. 

Changed the following lines: 

From : 

if { [string match "*profile0*" \$rx_clkout] }

To : 

if { [string match "*prof0*" \$rx_clkout] } 

A parallel loopback with an external VCXO design example that has been generated in Quartus® Prime Pro Edition software version 25.3 is not affected by this problem.