Went through this document and touched each graphic making sure there was valid "Alt text" for each. An older version of HelpNDoc copied Alt text from one photo to another. I did not enter text in all cases when adding a photo. This is a SEO exercise.
Back to the IO Pi. I think the problem is I don't understand the interrupt set-up.
With the Raspberry Pi being operated as a headless system, a way to safely stop and restart the processor would be nice. There is a wake-up pin on the board but no graceful reboot or shut down ~ that takes a pin and who has a pin? Longer discussion under Design Considerations.
When all else fails "Read the bloody manual!" is true again. During testing both the traffic module (Monitor class) and the interrupt function used the IOPi bus 2. I had the 4 monitoring LEDs set up on port 1 and LEDs driven by the interrupt (testing) function on port 0. By default when an address is assigned to a bus the library resets the whole bus as inputs. This can be bypassed, which is good because in the end one port on bus 2 will be inputs from Wabbits and the other port will be outputs for the traffic monitor.
More testing but setting the IOPi up correctly seems to also solve some odd behavior.
In frustration with the IOPi I built, installed and tested cabling between Wabbit feedback output and IOPi HAT.
New design for orientation of the two Unicorns. Small aesthetic improvement.
Close enough to adding the Raspberry Pi to the layout that I'm thinking about adding a guard to the edge of the layout to protect the "tall" stack of boards on the RPi.