Big components as SPI on BOOTLOAD use state-machine led debug : an integer contain the state of state machine, and this integer is displayed on 8 leds so you know where you are, it's for that I add several crash state in order to understand why and where component crash.
This project don't use IBM ROM of NEXYS2. Be careful if playing one day with it, physical IBM ROM is plugged on bottom of physical RAM and can put death bit for some byte address. In fact my 8th byte is death, '''it's why I turn always my upper RAM address bit into 1'''. I think that I have written on one time on a ghost part of ROM, and it was fatal...