Warning (169174): The Reserve All Unused Pins setting has not been specified

[Altera_Forum]

Hi, 

I am getting this annoying warning when my design is compiled: Warning (169174): The Reserve All Unused Pins setting has not been specified, and will default to 'As output driving ground'.  But when I check: Assignments > Device > Device and Pin Options, I see that the field "Unused Pins" is already set at "Reserve all unused pins: As output driving ground".  Why then am I getting this warning?  Regards,

[Altera_Forum]

Try changing it to a different value and see if the warning message changes. 

 Are you really sure you want the unused outputs to drive ground? If you do, then you must make sure to define all inputs and outputs in your top-level design that exist on the schematic, even if your HDL does not use them.  If you use this setting and do not define all inputs that are used on the FPGA, then the FPGA will drive those inputs (those that are on bidrectional pins anyway) and you will damage any external devices attempting to drive those FPGA inputs high.  Its rarely a good idea to use that setting.  Cheers, Dave

[Altera_Forum]

It can actually be a good idea to use this setting, if those pins are also connected to ground on your PCB, as it can help reduce ground bounce. Now I'm non really sure on how much it helps, and if the effect is measurable, but it can't do anything wrong! 

As you said though, you should make sure that those pins are indeed not externally connected to something else than ground, or bad things can happen.