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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@parasquid
The neopixels require fast pulses, and the usual way firmware for microcontrollers do it is to ride on I2S (instead of bitbanging gpio).
I2S usually need both SCK and LRCK defined, but the nRF52832 didn't need the LRCK pin defined. However after some testing (and a trip to the nordic forums) it seems it is indeed required.
What I meant by not accidentally using it is that since with nRF52 you can assign devices their pins, if you put LRCK it on an exposed pin, you might accidentally connect it to your circuit and have a really awful time debugging :P