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Thread: Issues with Arduino connecting to Teensy Loader

  1. #1
    Junior Member
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    Issues with Arduino connecting to Teensy Loader

    I recently got a teensy for a project. When I go to install any program, I get the following error:

    Unable find Teensy Loader. (p) Is the Teensy Loader application running?
    quitexit status 1
    Error compiling for board Teensy 3.5.

    The Teensy Loader application is running because Arduino opened it, but it still refuses to acknowledge that it exists.
    I am running Teensy Loader v1.45 and Arduino 1.8.8 on macOS Mojave.

    I have seen posts with this message on Linux, but have yet to find any solutions for macOS. Any idea what it could be?

  2. #2
    Senior Member PaulStoffregen's Avatar
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    This error means localhost communication between Arduino and Teensy Loader isn't working. It has nothing to do with USB or any hardware. It's purely software on your Mac.

    Why, I'm not sure. We sometimes used to see this on Windows when people had certain versions of the Zonealarm firewall. It would needlessly block localhost communication between programs running on the same machine.

    Is there any chance your Mac has extra security measures or special "sandbox" settings?

    I can tell you 1 other Mac user reported this same problem with Mojave a couple months ago. We never did figure out why. He apparently reinstalled MacOS and everything else and it worked, so no knowledge or insight gained about the problem.

    I can also tell you it works perfect on my Macbook Air with Mojave 10.14.2. Many people use Teensy on MacOS. This problem is rare, but not unheard of. I'm really hoping to learn what causes it....

  3. #3
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    There are no additional security measures. I have even tried turning off macOS's firewall and uploading, and still it won't work. I'm running a beta version of 10.14.3, so maybe that's it. I'll try updating and report back.

    Another thing to note is it did work for one program a few days ago onto a different teensy. I'll also look into if there are other Mojave-related localhost issues that are known.

  4. #4
    Senior Member PaulStoffregen's Avatar
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    Can you try with Verify instead of Upload.

    When you click Verify in Arduino, your code gets compiled and as a final step, it tells Teensy Loader the location of the freshly compiled code. But not uploading is attempted.

    Teensy Loader has an "Verbose Info" window. It's hidden in the Help menu (a place nobody ever looks...) This window will tell you lots of info, including what Teensy Loader is hearing from the various utilities Arduino runs.

  5. #5
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    Here's the info from that window. I had no idea it existed:

    16:01:39.972 (loader): Teensy Loader 1.45, begin program
    16:01:40.005 (loader): Unable to listen for remote control
    16:01:40.005 (loader): initialized, showing main window
    16:01:40.259 (loader): HID/macos: no devices found
    16:01:45.939 (loader): Verbose Info event

  6. #6
    Senior Member PaulStoffregen's Avatar
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    Wow, "Unable to listen for remote control" means we couldn't listen to a port for 127.0.0.1. Not good.

    I see Mojave 10.14.3 released today. I'm updating my Macbook Air now....

  7. #7
    Senior Member PaulStoffregen's Avatar
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    Upgraded to 10.14.3. Reinstalled Arduino 1.8.8 and Teensyduino 1.45 from fresh downloads. Everything seems to work fine. Here's a screenshot.

    Click image for larger version. 

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    (click for full size)

    The 3rd line in the Verbose Information window is what you're supposed to see, "Listening for remote control on port 3149"

  8. #8
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    The update fixed it! Must have been some issue with the beta version of macOS. Thank you for all your help! And now I know about the verbose information window.

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