18.104.22.168. Early I/O Assignment Analysis Without Design Files
You can perform basic I/O legality checks before defining HDL design files. This technique produces a preliminary board layout. For example, you can specify a target device and enter pin assignments that correspond to PCB characteristics. You can reserve and assign I/O standards to each pin, and then run I/O assignment analysis to ensure that there are no I/O standard conflicts in each I/O bank.
You must reserve all pins you intend to use as I/O pins, so that the Fitter can determine each pin type. After performing I/O assignment analysis, correct any errors reported by the Fitter and rerun I/O assignment analysis until all errors are corrected. A complete I/O assignment analysis requires all design files.