Re: OT - Any interest in starting a Tektronix Logic Analyzer Group? (with added bonus question!)


Harvey White
 

Interleaved comments
useful to demystify things like the I2C bus. Yes, there are other devices
(very cheap!  10 dollars) that can do that, but they are not data sensitive,
and there are times when I need that (what is byte XXX in message sent?)  For
me to *really* get an idea of what's going on, I'll need to write my own
protocol analyzer.
I've got a 10 dollar Saleae clone, and for a number of things, it's wonderful.  Does stuff that my HP16702B won't do without me digging into it and mastering what HP thought was simple.  I've got a fair amount of experience in programming, but I'm not sure that the HP is quite the right tool.
Hi Harvey; I don't follow... a common (and relatively cheap) protocol analyzer, such as a Beagle ( https://www.totalphase.com/products/beagle-i2cspi/ ), shows protocol details/data, and timing, with a little USB dongle. I have the I2C/SPI version, and the USB version. Works great for those specific serial buses.
Am I missing your point?
Yes, but it's because you don't have enough information to duplicate my viewpoint:

1) I just looked up the price of the Beagle.  I am now giving my wallet CPR....

2) I'm not sure that the beagle would do what I want.

The Saleae will take apart I2C (all that I'm interested in at the moment, and exactly what I needed when I was getting I2C packets working), and will tell me the exact binary/hex data stream. Wunnerful..... What it will NOT do, and can't, is to tell me that the header data field that specifies the type of chip I think I'm talking to is a PCA9634...  And it's in there some place when the packet destination is I2C.  Completely unreasonable for me to expect someone else to understand my custom data format for a packet, of course.

3) the Saleae will work only so fast and for so much data.  If I'm looking at the hardware itself, looking for glitches and unknown data patterns, and looking to see what else is going on in the system, sometimes the larger LA is better.  I did write, and have, written some descriptions for the HP that allow some taking apart and disassembly of the data stream.  On the other hand, I did that with a CPLD and took the serial data stream to a state/parallel stream, and used extra bits that the LA captured to identify address fields, start and stop data, etc.  Way before the Saleae was something I knew about.

I'm considering doing that in a program for an FPGA.  It captures the data and the auxiliary programming takes it apart.

Application example: A few years ago at HP, working on a storage controller that included a large SoC chip that included I2C for controlling power regulators in a startup sequence. Vendors docs were not detailed enough, and my power system design was a little different from their Reference Design, so there were issues. I used a Beagle to see and capture exactly what it was doing on power-up...
Hmmm, was teaching for the last 11 years or so, so I didn't have that resource (or that budget).  I think the problem is how specifically I can get the LA to interpret my data for me, and with the work I put into it, I rather expect it to be able to.


Simpler example, which I've needed multiple times: A CPU is trying to talk to something, but the I2C address is wrong. A Beagle immediately tells me what it's trying to do.
So does my LA, and so does the Saleae, for that matter.  I tend to have to develop applications from the ground up, and adding packet communications over I2C (which is piggybacked on an NRF24L01 protocol, hence 32 byte packets), was something I wished I had more (and easier) handles on), well....

So, for that matter, does the I2C address scanner I built into the project, pick the interface, and it pings everything on the bus by address.  It's a few menus down in the diagnostics.  Hit another touchscreen button and it (by address) tells you what you're talking to if it knows it, don't know who'd do that.

So for me, the bottom line goes several ways:

1) if it's low speed enough, and I don't need data analysis, and I don't need glitch information, but do need data... Saleae

2) if it's higher speed and I may need glitch information, the HP goes to work (I do have a Tek 308, it's cute, it's 16? channels, it's portable.  Did I mention it's cute?)

3) if I need exact packet analysis, then it's up to me to do the hardware and software.  Been there, doing that....

Not likely that I'm doing typical stuff, depending.

I'd like to get my 7D02 working, but that's not likely for now. Actually easier to go build the equivalent from scratch, which I just might do... I could look at some of the older 8 bit processors in the Tek stuff I have, that may not be working.

Thanks for the comments.

Harvey


Pete


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