When Your Logic Analyzer Can’t Tell Good And Bad Signals Apart

[Avian] has picked up a Miniware LA104 – a modest battery-driven logic analyzer with builtin protocol decoders. This sort of analyzers are helpful instruments for when you quickly need to have to see what definitely is occurring with a selected sign, and they are low-priced more than enough to be sacrificial when it arrives to dangerous repairs. Regrettably, he stumbled upon a peculiar trouble – the analyzer would exhibit the sign glitching each and every now and then, even at quite minimal bitrates. Even far more incredibly, the glitches did not happen in the signal traces when exported and seen on a notebook.

A Pulseview window showing that the problem is not present in the exported capturesHe dug into the challenge, as [Avian] does. Likely as a result of the problem-ridden capture information aided him comprehend that the glitch would always materialize when a single of the sign edges would be delayed by a couple of microseconds relative to other signal edges — a frequent event when it comes to electronic logic. This looks to stem from compression remaining utilized by the FPGA-powered “capture samples and deliver them” element of the analyzer. This bug only relates to the signal as it’s becoming exhibited on the analyzer’s screen, and turned out that when most of this analyzer’s interface is drawn by the STM32 CPU, the trace drawing portion specifically was finished by the FPGA working with a individual Lcd interface.

It would look Miniware didn’t do plenty of tests, and it’s impossible to distinguish a good signal from a faulty one when using a LA104 – arguably, the most important perform of a logic analyzer. In the most effective of Miniware traditions, going as far as becoming hostile to open up-resource firmware at occasions, the FPGA bistream supply code is proprietary. Hence, this bug is not anything we can easily take care of ourselves, until Miniware methods up and releases a gateware update. Until finally then, if you bought a LA104, you cannot count on the sign it exhibits on the monitor.

When it comes to Miniware problems, we have not long ago lined a Miniware tweezer mend, requiring a redesign of the shell at first held together with copious quantity of glue. At moments, it feels like there is some thing in common between glue-crammed unrepairable devices and faulty proprietary firmware. If this bug ruins the LA104 for you, hey, at least you can reflash it to function as an electronics interfacing multitool.