Turning the Freedom board into a Logic Analyzer

in logic analyzer by DP | 3 comments

i2c-capture-with-decoder

Erich Styger of MCUonEclipse writes:

I think the most important tool for a firmware engineer is a Logic Analyzer. I always have one on my desk. Working in different locations, sometimes I forget to carry it with me. And for sure I would need it. To buy another one to compensate my laziness? Or maybe there is another solution? And here I stumbled over an article about the Logic Sniffer project recently: it is about an open source logic analyzer hardware and firmware project. What a cool idea! Why not using my FRDM-KL25Z Freedom board as a Logic Analyzer? Heck, that would be awesome :-)

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Comments

  1. For situations where the samples will fit in RAM, this is good.
    For long sampling periods I used a USBasp and a PL-2303HX to make a logic analyzer that can sample 2 lines at 2.4 msps or 8 lines at 600ksps.
    http://nerdralph.blogspot.ca/2014/05/24-megasamples-per-second-continuous.html

    • Max says:

      In my experience, the OLS RAM in RLE mode is mostly adequately large – the big failure of OLS in my opinion is lack of either a _properly_ large post-trigger delay counter (the existing one is 32 bit large, in sampling clocks – WTF?!? No, let me just say it again: WTF?!?) or a trigger re-occurence counter (trigger must activate ‘n’ times before starting to acquire) and unfortunately I don’t expect those getting any better. DSLogic seems to have addressed those by the way, I’m keeping an eye on them for when they start selling publicly. Interesting take with the LA-out-of-an-USBasp by the way… :)

      • Max, I agree that with RLE, a few KB of RAM is usually good enough for a logic analyzer. I haven’t found any really cheap OLS clients that will do RLE though. Here’s one example:
        https://github.com/gillham/logic_analyzer
        Because of that, I’ve been thinking of doing it myself. I’ve come close to getting capture and RLE in 5 cycles using AVR assembler, which would support 4msps on a 20Mhz AVR.

        Another idea I have is using an AVR and a cheap dollar-store USB-microSD reader to make a 20msps 4-bit logic capture device. SD nibble mode supports a minimum of 25Mhz – so a 20Mhz could do the initialization and setup, and with an external mux connect 4 data lines to the SD bus during the block transfer.

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