ws2812-flexio

A neopixel driver based on NXP i.MX RT's FlexIO bus.

Pixel Type

The default color space of NeoPixel LED strips is 8-bit linear sRGB, therefore the recommended pixel type is LinSrgb<u8>.

Be aware that this differs from normal, gamma corrected sRGB; a conversion has to take place. More info can be found in the documentation of the palette crate.

Operating Modes

This crate can operate either in blocking mode or in DMA driven asynchronous mode.

Specs

Parallel strips

The library can drive multiple strips in parallel. To be more specific, driving multiple strips from the same FlexIO instance requires 2 + 2 * strips FlexIO timers, so a for example a FlexIO instance with 8 timers can drive 3 strips in parallel.

Framerate

The library drives the LED strips at 800kHz with a latch time of 300us. This gives us the following formula:

fps = 100,000 / ((num_pixels + 1) x bytes_per_pixel + 30)

Example: For a strip with 332 SK6805 pixels, we can achieve 100,000 / ((332 + 1) * 3 + 30) = 97.18 fps.

Be aware that this framerate is only realistic for DMA based writes; with blocking writes, additional time gets lost while the next frame gets computed.

Examples

- examples are intended for the Teensy 4.0 board -

Prerequisites

The following hardware is required for the examples:

• A Teensy 4.0 development board
• A way to read the Teensy's UART, like a USB-UART-converter

The following software tools have to be installed:

• Python3 (as python3, or modify run.py to use the python binary)
• llvm-objcopy
  • Install LLVM tool suite
• teensy-loader-cli

Run

• Connect the Teensy to PC via USB cable.
• Run cargo run --release --example triple_332.
• Read the output of the examples on the Teensy's UART.
• Pin 6, 7 and 8 output data for NeoPixel RGB strips of length 332 each (for example P/N: S010332ZA3SA8). Note that those pins output 3.3V, and most NeoPixel LED strips require a 5V data signal, which means an external level shifter is required.