Lights!

source: Adafruit Neopixel Uberguide

This module may lack a screen, but the 22 "neopixel" lights arranged around the edge on the backside are bright (2.5W/each at full white) and individually addressable with 24 bits of color (8 per channel, rgb). Provided is ui/color_ring.h, a collection of utility functions that manipulate the lights:

• Pixel: a union between uint32_t and a struct that accesses the first three bytes as uint8_t
• #ws2812_control_init: initialize the RMT peripheral for writing out to the neopixels
• #ws2812_write_leds: copy the given buffer to the RMT DMA buffers for output (flush)
• #pixel_rgb: a factory function for producing Pixel instances
• #rgb_spectrum: a helper function for producing "rainbow" gradients
• #ring_dim: linearly scale the brightness of all the neopixels
• #ring_fill: given a Pixel, set all of the lights to the that color
• #ring_fill_rainbow: using #rgb_spectrum, paint a rainbow from red through to violet

The two rotation animation functions are a bit special and are worth specific attention, so don't worry about them, yet.

Before the rmt peripheral can be used, it has to be initialized with #ws2812_control_init. Flush the color buffer with #ws2812_write_leds.

#include "ui/color_ring.h"

struct led_state ring;

static void red_dots()
{
    // black out everything
    ring_fill(pixel_rgb(0, 0, 0), &ring);

    for (int k = 0; k < NUM_LEDS; K+=2)
    {
        ring.leds[k].components.r = 20;
    }
    ws2812_write_leds(ring);
}
...
void app_main()
{
    ws2812_control_init();
    red_dots();
}