Paul Clarke was a CD-i developer at Philips ADS (Advanced Development & Support) within Philips Research based in Redhill, UK. He built and designed the NIRD (Non-Intrusive Real-time Debugger), which was used as a real-time debugger in the form of a cartridge about the size of a DV cart that plugs in the DV slot of a CD-i player, with a through connector and cradle so a DV cart can then be plugged in. There's then some PC software that you use when running it. Below you see Paul working on it (picture taken in 1994):
It samples the address, data and control bus of the CD-I processor as exposed on the expansion port and saves 16384 bus cycles in a round robin format until it spots a bug. You then download up to 16384 cycles before the bug to the PC where I wrote a bus cycle disassembler that shows you what went wrong, even down to C-source level if you like. I got a patent for it - see link here and you can find out more about my current work here"
The ADS team paid tribute to the power of N.I.R.D in this touching credit screen from Arcade Classics. The definition of N.I.R.D is Non-Intrusive Real-time Debugger:
[Thanks, Paul Clarke, the author of the N.I.R.D.]