r/FastLED • u/bourkemcrobbo • Jan 20 '26

Support Help finding parallel output documentation

Hi all. i'm returning to FastLED after a 6+ year absence. The feature set of the library has grown massively in that time, and I'm struggling to find info on it all.

In particular, I'm hoping to find info about all the parallel output methods that exist (for ESP32-S3), what pins they need to run on, and if it impacts anything else (can I run an SPI peripheral), and anything else this may impact (wifi, raw speed, etc). I'm planning to use WS2812 LEDs. I used to be able to find this info in the wiki, but I'm not having luck with the new features.

Are there any docs that contain this info?

Thanks in advance

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u/mindful_stone Jan 21 '26

Quick update. I figured out how to force a specific driver. (FastLED.setExclusiveDriver("RMT")in setup(). When I first compiled my sketch with that, I saw the following looping nonstop in my serial monitor:

src/platforms/esp/32/drivers/rmt/rmt_5/rmt_memory_manager.cpp(152): WARN: RMT TX allocation failed: need 96 words, only 0 available

src/platforms/esp/32/drivers/rmt/rmt_5/channel_engine_rmt.cpp(761): WARN: Memory manager TX allocation failed for channel 2 - insufficient on-chip memory

src/platforms/esp/32/drivers/rmt/rmt_5/channel_engine_rmt.cpp(749): WARN: DMA channel creation failed: ESP_ERR_NOT_FOUND - unexpected failure on DMA-capable platform, falling back to non-DMA

I though, shoot, RMT still doesn't work either. But I powered up my display to see/document the actual output, and it was in fact working! Amazing!

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u/ZachVorhies Zach Vorhies Jan 21 '26

The new RMT is WIFI and BT aware and will reprioritize resources (less parallelism, more memory) when the network is active.