220.127.116.11. I/O Assignment Analysis With Design Files
I/O assignment analysis allows you to perform full I/O legality checks after fully defining HDL design files. When you run I/O assignment analysis on a complete design, the tool verifies all I/O pin assignments against all I/O rules. When you run I/O assignment analysis on a partial design, the tool checks legality only for defined portions of the design. The following figure shows the work flow for analyzing pin-outs with design files.
Even if I/O assignment analysis passes on incomplete design files, you may still encounter errors during full compilation. For example, you can assign a clock to a user I/O pin instead of assigning to a dedicated clock pin, or design the clock to drive a PLL that you have not yet instantiated in the design. This issues occur because I/O assignment analysis does not account for the logic that the pin drives and does not verify that only dedicated clock inputs can drive the a PLL clock port.
To obtain better coverage, analyze as much of the design as possible over time, especially logic that connects to pins. For example, if your design includes PLLs or LVDS blocks, define these files prior to full analysis. After performing I/O assignment analysis, correct any errors reported by the Fitter and rerun I/O assignment analysis until all errors are corrected.
The following figure shows the compilation time benefit of performing I/O assignment analysis before running a full compilation.