A friend of mine learned to write linux kernel drivers. We had to write tests for hardware of a big name manufacturer. We had a USB cd-rom drive that failed some test unexplainably. We contacted the engineers and they were very responsive about the firmware, we also performed many mechanical tests. My friend decided to flex his driver writing muscles and spent a whole day modifying the linux kernel to carefully investigate bit by bit what was being sent from the cd-rom. After a very long investigation he categorically said: "It can only be the cable."

It was the cable indeed. And we could have discovered with much less effort.