SPI Tap: Logging external signals using D4-D15 inputs

It would be very helpful to be able to log signals (other than Select) in the SPI capture log. These signals could be other inputs or outputs to/from the SPI device under test, or signals specifically generated in software to mean "I'm DOING THIS TASK NOW".

Development boards usually have many extra signals, and the SPI-TAP has many extra inputs. Being able to synchronize and record signals and packets would be awesome!