Finally have no critical warnings on my synthesis. Turns out my circular reference was my own fault (not surprising). I forgot to put registers on the carry-out and A=B pins from the 74181 module. They fed straight to the databus which fed right back to the 74181. Next up is writing a piece of code which I can verify is working. I may throw for the endzone and send data to the UART first. And then when the ball bounces off the helmet of my receiver, I'll use the LEDs and buttons of the Cmod board. And probably also the GPIO pins and my logic analyzer. I may create an LED register and pass that out. It would make for some good pictures and I think people like those a lot. And prove I'm actually making something...