MSO and USB LA owners

[rs20]

AFAIK a logic analyser has never been about showing live streams and I don't know of any logic analyser which can show live streams at a decent speed. A logic analyser has always been about capturing signals and analysing them afterwards. At least that is how I have always been using them.

You appear to be correct, the general consensus is exactly that, not a terribly satisfying argument: "LA's don't show live data because that's not what LA's do". Which is why I don't want a logic analyser. What I want is a USB MSO minus the analog channels; but as far as I can tell, such a thing doesn't exist because people will tell you "that's a logic analyzer"*, but then if you get a logic analyzer, you lose the live monitoring functionality that is so central to many debugging workflows. I just can't get my head around why people are happy with this state of affairs, but evidently my workflows are wrong and I should feel bad.

* And so what I got was a USB MSO with the analog channels, and I would be strongly tempted to do so even if I did purely digital work!?

[Berni]

Yes such a thing is only a software feature. The SPI decode is so fast that it could run in real time. You could run the hardware in continuous capture mode since triggering is also done on the PC side.

Saleae is not the best out there, but the basic features that it has work very well and you can get knockoff hardware for it very cheaply.

If you need a real big boy LA then you will know you need one. But most of you out there won't ever need it.(I never have)

[nctnico]

Yes such a thing is only a software feature. The SPI decode is so fast that it could run in real time.

But even then you have to ask yourself what the actual value is of such a feature. I have an Agilent MSO and the decoded serial data usually changes so fast that the only thing you notice are the numbers changing. You can't tell whether the numbers are right or wrong (and just forget about spotting an anomaly).

[rs20]

But even then you have to ask yourself what the actual value is of such a feature. I have an Agilent MSO and the decoded serial data usually changes so fast that the only thing you notice are the numbers changing. You can't tell whether the numbers are right or wrong (and just forget about spotting an anomaly).

How about seeing live feedback and checking for correlation between the real world and the measurements on screen -- gyroscope, accelerometers, light sensors, ADCs reading DC values... USB lines in response to different keystrokes. Low data rate applications like clap sensors. I mean really, just try to contrive any situation in which an SPI line produces small amounts of sporadic data, OR even large amounts of highly repeatably structured data. Also, set up a glitch filter/trigger of some sort, and manipulate the device to see exactly when glitches occur.

It may well be true that the serial lines that you interact with are carrying huge numbers of bytes per second, or unstructured data that requires deep interpretation. But since when were test instruments about focussing on one use case at the exclusion of all others? It's crazy to take a discussion the LA's should have this feature and flip it into an assertion that even MSO's shouldn't, especially when most MSOs provide it and some even provide ASIC implementations for even more speed. Seems like an awful load of bother to go to for a feature of no "actual value".

[tautech]

While LA's might have unlimited storage and that being their great advantage isn't the MSO's trigger suite the work around to compensate for lack of a large memory. Sure one has to be somewhat intimate with the data stream to know where to inspect the stream. Or is it just too hard?

Who uses: Window, Interval, Dropout, Runt or Pattern triggers?
Each of which contain subsets of parameters to further refine what are quite standard additional trigger types in a DSO, nevermind an MSO.

Then there's the sets of Decode triggers, each with further subsets of user definable conditions, so many so that how can you not find what you seek?

Segmented memory and History capable DSO's.
Are these other features that are under utilised?

Can we liken advanced scope use to driving an auto shift car compared to an 18sp Roadranger truck box, the RR just takes practice.....lots.

[LabSpokane]

When using a borrowed USB LA for the first time, I was absolutely astonished to discover that the LA could not be configured to display a live stream of SPI data on my screen.

Someone correct me, but I believe low-end USB LAs of the Saleae variety (what I have) don't decode in hardware.  They actually are directly sampling and storing samples of the waveforms and can only store in computer RAM.  This is done for acquisition speed reasons.  I don't think changing this is trivial, at least not on a $150 USB LA. 

 Keysight (and others?) decode in hardware, and that makes live streams practical.

AFAIK a logic analyser has never been about showing live streams and I don't know of any logic analyser which can show live streams at a decent speed. A logic analyser has always been about capturing signals and analysing them afterwards. At least that is how I have always been using them.

Yes.  I should have qualified "live."  The scope is easier to capture and view a recent data stream than a USB logic analyzer.  But that's it.  You're absolutely correct that neither is live and only captures for later analysis. 

[free_electron]

MSO or Scope synced to a real logic analyser ( like syncing an infiniium to a 16902 series )