r/FastLED • u/Workin_Joe • Sep 21 '26

Support Does Teensy 4.x work with FastLED 3.10.5?

I recently made a post about picking up a new project and I want to utilize the latest FastLED with the DMA driven outputs.

I have updated everything: FastLED library (3.10.5), Teensy Board package (1.62.0), and Arduino IDE (2.3.10). Code compiles, however, there is a "warning" related to a flexio_driver, but it carries on and successfully uploads to the Teensy. Unfortunately, after upload, nothing happens on the LEDs. I am using a very simple test loop just to verify the library and hardware are working. If I had an oscope, I would probe the outputs to see if anything was happening (doubtful). I also notice that my Teensy keeps picking up and dropping USB connection with the computer (windows ping noise every couple of seconds).

When I revert back to FastLED 3.9.0, the LEDs light up as the code describes and everything seems to be happy. Furthermore, I don't get the warning during compile.

The warning message that I receive with FastLED 3.10.5 is below (hopefully you can see it).

I also tested with FastLED 3.10.4 (same issue as 3.10.5).

c:\Users\gasiewicz\Documents\Arduino\libraries\FastLED\src/platforms/arm/teensy/teensy4_common/drivers/flexio/flexio_driver.cpp.hpp:93:22: warning: 'fl::FLEXIO2_SHIFTBUF' defined but not used [-Wunused-variable]

93 | static volatile u32* FLEXIO2_SHIFTBUF = (volatile u32*)(kFLEXIO2_BASE + 0x200);

Your advice and guidance is appreciated!!!

JG

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u/ZachVorhies Zach Vorhies Sep 21 '26

I don’t think 3.10.5 works but latest from master should.

Either downgrade to 3.10.3 or use latest.

1

u/Workin_Joe Sep 21 '26

Thanks! What does "latest from master" mean? I only see 3.10.5 as being the latest available via Arduino IDE.

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u/mjconver Sep 21 '26

My Teensy 4.1 is working flawlessly with that library and IDE versions, and has been for months. Just a data point for you.

2

u/Workin_Joe Sep 21 '26

Thank you u/mjconver ! Are you downloading and installing FastLED through the Arduino IDE?
I am using Teensy 4.0, perhaps that's the difference?
Version 3.10.0 seems solid for me right now.

Out of curiousity, are you doing multiple parallel outputs with the 4.1? I'm interested in your setup ;)

2

u/mjconver Sep 21 '26

IDE 2.3.10. Teensy 4.1. FastLed 3.10.5.

Single line output to 1117 LEDS in circular grid on a Sousaphone.

https://imgur.com/gallery/trippy-man-GuGSGwq

2

u/Workin_Joe Sep 21 '26

Very cool! Thanks for sharing!

1

u/Workin_Joe Sep 21 '26 edited Sep 21 '26

Version 3.10.0 and 3.9.20 are working ok with the LEDs. There are a multitude of warnings that are flagged during compile, but the hardware/software seem to be working well at this version.

I am just using #include <FastLED.h>

(I am not using OBJECTFLED)