docs(feat): further generalize RGB information (#2485)

* docs(feat): Provide example of PIO SPI for RGB underglow

* docs(feat): further generalize RGB information

* docs: use nice_nano_v2 for board-specific shield config example

Co-authored-by: Cem Aksoylar <[email protected]>

---------

Co-authored-by: Cem Aksoylar <[email protected]>

1 files changed, 89 insertions, 72 deletions

diff --git a/docs/docs/features/underglow.md b/docs/docs/features/underglow.md
index ba6c009234..4802b92bf2 100644
--- a/docs/docs/features/underglow.md
+++ b/docs/docs/features/underglow.md
@@ -6,16 +6,16 @@ sidebar_label: RGB Underglow
 RGB underglow is a feature used to control "strips" of RGB LEDs. Most of the time this is called underglow and creates a glow underneath the board using a ring of LEDs around the edge, hence the name. However, this can be extended to be used to control anything from a single LED to a long string of LEDs anywhere on the keyboard.
 
 :::info
-RGB underglow can also be used for under-key lighting. If you have RGB LEDs on your keyboard, this is what you want. For PWM/single color LEDs, see [Backlight](backlight.mdx).
+RGB underglow can also be used for per-key lighting. If you have RGB LEDs on your keyboard, this is what you want. For PWM/single color LEDs, see [Backlight](backlight.mdx).
 :::
 
-ZMK supports all the RGB LEDs supported by Zephyr. Here's the current list supported:
+ZMK relies on Zephyr's `led-strip` drivers for this feature. The following LEDs/LED families have been implemented:
 
-- WS2812-ish (WS2812B, WS2813, SK6812, or compatible)
+- WS2812 (includes WS2812B, WS2813, SK6812, and others)
 - APA102
-- LPD880x (LPD8803, LPD8806, or compatible)
+- LPD880x (includes LPD8803, LPD8806, and others)
 
-Of the compatible types, the WS2812 LED family is by far the most popular type. Currently each of these types of LEDs are expected to be run using SPI with a couple of exceptions.
+The WS2812 LED family is by far the most popular of these types, so this page will primarily focus on working with it.
 
 Here you can see the RGB underglow feature in action using WS2812 LEDs.
 
@@ -34,16 +34,15 @@ CONFIG_ZMK_RGB_UNDERGLOW=y
 CONFIG_WS2812_STRIP=y
 ```
 
-See [Configuration Overview](/docs/config) for more instructions on how to
-use Kconfig.
+See [Configuration Overview](/docs/config) for more instructions on how to use Kconfig.
 
 If your board or shield does not have RGB underglow configured, refer to [Adding RGB Underglow to a Board](#adding-rgb-underglow-to-a-board).
 
 ### Modifying the Number of LEDs
 
-A common issue when enabling underglow is that some of the installed LEDs do not illuminate. This can happen when a board's default underglow configuration accounts only for either the downward facing LEDs or the upward facing LEDs under each key. On a split keyboard, a good sign that this may be the problem is that the unilluminated LEDs on each half are symmetrical.
+The number of LEDs specified in the default configuration for your board or shield may not match the number you have installed. For example, the `corne` shield specifies only 10 LEDs per side while supporting up to 27. On a split keyboard, a good sign of this mismatch is if the lit LEDs on each half are symmetrical.
 
-The number of underglow LEDs is controlled by the `chain-length` property in the `led_strip` node. You can [change the value of this property](../config/index.md#changing-devicetree-properties) in the `<keyboard>.keymap` file by adding a stanza like this one outside of any other node (i.e. above or below the `/` node):
+The `chain-length` property of the `led_strip` node controls the number of underglow LEDs. If it is incorrect for your build, [you can change this property](../config/index.md#changing-devicetree-properties) in your `<keyboard>.keymap` file by adding a stanza like this one outside of any other node (i.e. above or below the `/` node):
 
 ```dts
 &led_strip {
@@ -51,7 +50,7 @@ The number of underglow LEDs is controlled by the `chain-length` property in the
 };
 ```
 
-where the value is the total count of LEDs (per half, for split keyboards).
+For split keyboards, set `chain-length` to the number of LEDs installed on each half.
 
 ## Configuring RGB Underglow
 
@@ -59,16 +58,23 @@ See [RGB underglow configuration](/docs/config/underglow).
 
 ## Adding RGB Underglow to a Board
 
-RGB underglow is always added to a board, not a shield. This is a consequence of needing to configure SPI to control the LEDs.
-If you have a shield with RGB underglow, you must add a `boards/` directory within your shield folder to define the RGB underglow individually for each board that supports the shield.
-Inside the `boards/` folder, you define a `<board>.overlay` for each different board.
-For example, the Kyria shield has a `boards/nice_nano.overlay` file that defines the RGB underglow for the `nice_nano` board specifically.
+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.
+
+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`](https://github.com/zmkfirmware/zmk/blob/main/app/boards/shields/kyria/boards/nice_nano_v2.overlay) and a [`boards/nrfmicro_13.overlay`](https://github.com/zmkfirmware/zmk/blob/main/app/boards/shields/kyria/boards/nrfmicro_13.overlay), which configure a WS2812 LED strip for the `nice_nano_v2` and `nrfmicro_13` boards respectively.
 
 ### nRF52-Based Boards
 
-With nRF52 boards, you can just use `&spi3` and define the pins you want to use.
+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](https://docs.nordicsemi.com/bundle/ps_nrf52840/page/pin.html).
+
+:::
 
-Here's an example on a definition that uses P0.06:
+The following example uses `P0.06` as the "Data In" pin of a WS2812-compatible LED strip:
 
 ```dts
 #include <dt-bindings/led/led.h>
@@ -89,38 +95,31 @@ Here's an example on a definition that uses P0.06:
 };
 
 &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>;
-  };
+    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>;
+    };
 };
 ```
 
-:::info
-
-If you are configuring SPI for an nRF52 based board, double check that you are using pins that aren't restricted to low frequency I/O.
-Ignoring these restrictions may result in poor wireless performance. You can find the list of low frequency I/O pins for the nRF52840 [here](https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf52840%2Fpin.html&cp=4_0_0_6_0).
-
-:::
-
 :::note
 
 Standard WS2812 LEDs use a wire protocol where the bits for the colors green, red, and blue values are sent in that order.
@@ -130,34 +129,60 @@ If your board/shield uses LEDs that require the data sent in a different order,
 
 ### Other Boards
 
-For other boards, you must select an SPI definition that has the `MOSI` pin as your data pin going to your LED strip.
+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.
 
-Here's another example for a non-nRF52 board on `spi3`:
+For example: the `sparkfun_pro_micro_rp2040` board can utilize SPI via PIO to run a WS2812 strip on `GP0`:
 
 ```dts
 #include <dt-bindings/led/led.h>
 
-&spi3 {
+&pinctrl {
+    pio0_spi0_default: pio0_spi0_default {
+        group1 {
+            pinmux = <PIO0_P0>;
+        };
+    };
+};
 
-  led_strip: ws2812@0 {
-    compatible = "worldsemi,ws2812-spi";
-
-    /* SPI */
-    reg = <0>;
-    spi-max-frequency = <5250000>;
-
-    /* WS2812 */
-    chain-length = <10>; /* number of LEDs */
-    spi-one-frame = <0x70>; /* make sure to configure this properly for your SOC */
-    spi-zero-frame = <0x40>; /* make sure to configure this properly for your SOC */
-    color-mapping = <LED_COLOR_ID_GREEN
-                          LED_COLOR_ID_RED
-                          LED_COLOR_ID_BLUE>;
-  };
+&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>;
+        };
+    };
 };
 ```
 
-Once you have your `led_strip` properly defined you need to add it to the root devicetree node `chosen` element:
+### Final Steps
+
+Once the `led_strip` is properly defined, add it to the `chosen` node under the root devicetree node:
 
 ```dts
 / {
@@ -166,11 +191,3 @@ Once you have your `led_strip` properly defined you need to add it to the root d
     };
 };
 ```
-
-Finally you need to enable the `CONFIG_ZMK_RGB_UNDERGLOW` and `CONFIG_*_STRIP` configuration values in the `.conf` file of your board (or set a default in the `Kconfig.defconfig`):
-
-```ini
-CONFIG_ZMK_RGB_UNDERGLOW=y
-# Use the STRIP config specific to the LEDs you're using
-CONFIG_WS2812_STRIP=y
-```