Hey, I have two questions regarding IO cells. a) What's the difference between IOPadVss and IOPadIOVss? I saw Metal2 is not connected from the cell to the PG ring in IOPadIOVss. I'm wondering if I could just use IOPadVss only since I don't care about isolated ground between the ring and core. b) Are there any recommendations about how many power and ground pins a design should have?

For (a), no you definitely need both, they are not connected internally, so unless you redesign those pads, you need both. You could of course just put each next to each other and have them bonded out to the same package pad if you want to ...

Thanks @tnt, good to know. I'm gonna open a "feature request" in Github 😉

The reason there are two different cells is to minimize the noise of the current from the output drivers of the IO cells on the ground for the core area. This is similar to star connections for GND/VDD on PCB.