I went kind of overboard looking into issues with Altera USB Blaster clones a couple of years ago. While writing that post, I ran into some really frustrating intermittent problems in Linux with jtagd that I was never able to figure out:
I also experienced a really weird unrelated problem in Quartus Programmer 18.1 in Linux while I was testing things on one of my computers. I could see corrupted outgoing USB traffic in my Wireshark capture — before the FT245 or CPLD were even involved in the equation. This problem affected all of my blasters, not just the CPLD+FT245 ones.
I still sometimes notice a long (~30 second) delay the first time I try to do a JTAG operation in Linux after plugging in any of my CPLD-based USB Blasters. It doesn’t happen every time, but when it does, it seems like jtagd is hung up waiting to receive a byte, which never happens, so it times out and tries again. It works fine after that.
Since I was already exhausted from dealing with all of the other USB Blaster problems at the time, I completely lost interest in digging further into these particular nagging issues, so I left them alone. Until now. AI has opened up the ability for some of these little mysteries to be closed out without having to spend a bunch of time investigating them. Believe me, debugging can be an exciting challenge, but intermittent issues are just not fun to diagnose at all.
Read the rest of this entry
