RGB Underglow

Please see lighting feature page for an introduction on the feature.

Support for RGB underglow is always added to a board, not a shield. This is because the LED strip drivers rely on hardware-specific interfaces (e.g. SPI, I2S) and configurations, which shields do not control. See the documentation page on pin control for detailed information on setting up pins for hardware protocols such as SPI or PIO that are used for LED strips.

Shields written for boards which support RGB underglow should add a boards/ folder underneath the shield folder. Inside this boards/ folder, create a <board>.overlay for any of the boards the shield can be used with. Place all hardware-specific configurations in these .overlay files.

For example: the kyria shield has a boards/nice_nano_v2.overlay and a boards/nrfmicro_13.overlay, which configure a WS2812 LED strip for the nice_nano_v2 and nrfmicro_13 boards respectively.

nRF52-Based Boards

Using an SPI-based LED strip driver on the &spi3 interface is the simplest option for nRF52-based boards. If possible, avoid using pins which are limited to low-frequency I/O for this purpose. The resulting interference may result in poor wireless performance.

info

The list of low frequency I/O pins for the nRF52840 can be found here.

The following example uses P0.06 as the "Data In" pin of a WS2812-compatible LED strip:

#include <dt-bindings/led/led.h>

&pinctrl {
    spi3_default: spi3_default {
        group1 {
            psels = <NRF_PSEL(SPIM_MOSI, 0, 6)>;
        };
    };

    spi3_sleep: spi3_sleep {
        group1 {
            psels = <NRF_PSEL(SPIM_MOSI, 0, 6)>;
            low-power-enable;
        };
    };
};

&spi3 {
    compatible = "nordic,nrf-spim";
    status = "okay";

    pinctrl-0 = <&spi3_default>;
    pinctrl-1 = <&spi3_sleep>;
    pinctrl-names = "default", "sleep";

    led_strip: ws2812@0 {
        compatible = "worldsemi,ws2812-spi";

        /* SPI */
        reg = <0>; /* ignored, but necessary for SPI bindings */
        spi-max-frequency = <4000000>;

        /* WS2812 */
        chain-length = <10>; /* number of LEDs */
        spi-one-frame = <0x70>;
        spi-zero-frame = <0x40>;
        color-mapping = <LED_COLOR_ID_GREEN
                         LED_COLOR_ID_RED
                         LED_COLOR_ID_BLUE>;
    };
};

note

Standard WS2812 LEDs use a wire protocol where the bits for the colors green, red, and blue values are sent in that order. If your board/shield uses LEDs that require the data sent in a different order, the color-mapping property ordering should be changed to match.

Other Boards

Be sure to check the Zephyr documentation for the LED strip and necessary hardware bindings. Not every board has an spi3 node, or configures pinctrl the same way. Reconcile this with any hardware restrictions found in the manufacturer's datasheet. Additional hardware interfaces may need to be enabled via Kconfig.

For example: the sparkfun_pro_micro_rp2040 board can utilize SPI via PIO to run a WS2812 strip on GP0:

#include <dt-bindings/led/led.h>

&pinctrl {
    pio0_spi0_default: pio0_spi0_default {
        group1 {
            pinmux = <PIO0_P0>;
        };
    };
};

&pio0 {
    status = "okay";

    pio0_spi0: pio0_spi0 {
        pinctrl-0 = <&pio0_spi0_default>;
        pinctrl-names = "default";

        compatible = "raspberrypi,pico-spi-pio";
        #address-cells = <1>;
        #size-cells = <0>;
        clocks = <&system_clk>;
        clock-frequency = <4000000>;

        clk-gpios = <&gpio0 10 GPIO_ACTIVE_HIGH>;     /* Must be defined. Select a pin that is not used elsewhere. */
        mosi-gpios = <&pro_micro 1 GPIO_ACTIVE_HIGH>; /* Data In pin. */
        miso-gpios = <&pro_micro 1 GPIO_ACTIVE_HIGH>; /* Must be defined. Re-using the DI pin is OK for WS2812. */

        led_strip: ws2812@0 {
            compatible = "worldsemi,ws2812-spi";

            /* SPI */
            reg = <0>; /* ignored, but necessary for SPI bindings */
            spi-max-frequency = <4000000>;

            /* WS2812 */
            chain-length = <10>; /* number of LEDs */
            spi-one-frame = <0x70>;
            spi-zero-frame = <0x40>;
            color-mapping = <LED_COLOR_ID_GREEN
                             LED_COLOR_ID_RED
                             LED_COLOR_ID_BLUE>;
        };
    };
};

Final Steps

Once the led_strip is properly defined, add it to the chosen node under the root devicetree node:

/ {
    chosen {
        zmk,underglow = &led_strip;
    };
};