The intention is to ignore pins that must not be driven by firmata because doing so would brake the firmata stream (that's why there are both SS-pins of the ethernet-shield listed in there). Then I noticed that you get the 'Unknown pin mode' error from FirmataExt when the systemResetCallback initializes the pinmodes for all pins from 1 to TOTAL_PINS. Actually since we currently don't have a way to reliably determine which pins are unsuitable for firmata-use I added this as a place where the user can configure (or overide the defaults).