add SK6812 RGBW 4-channel LEDs

docs/LedStrip.md

@@ -89,6 +89,8 @@ It could be possible to be able to specify the timings required via CLI if users
   * Fits well under motors on mini 250 quads.
 * [Adafruit NeoPixel Stick](https://www.adafruit.com/products/1426) (works well)
   * Measured current consumption in all white mode ~ 350 mA.
+* [Aliexpress SK6812 RBGWW strip](https://www.aliexpress.com/wholesale?SearchText=rgbw+sk6812) (works well)
+  * Alternative [Adafruit NeoPixel Stick RGBW](https://www.adafruit.com/product/2869)
 
 
 ### WS2811 vs WS2812
@@ -97,6 +99,8 @@ The [WS2811](https://cdn-shop.adafruit.com/datasheets/WS2811.pdf) is a LED drive
 
 The [WS2812](https://cdn-shop.adafruit.com/datasheets/WS2812.pdf) is integrated into the package of a 50:50 LED rather than as a separate device. It accepts data in the form of 8 bits each of Green-Red-Blue.
 
+With the [SK6812](https://cdn-shop.adafruit.com/product-files/1138/SK6812+LED+datasheet+.pdf) also GRBW variants are supported, which have a fourth (white) channel and such provide a much cleaner white color.
+
 It is thus possible, depending on the LED board/strip being used that either Red-Green-Blue or Green-Red-Blue encoding may be required. This may be controlled by setting the following.
 
 ```
@@ -107,8 +111,14 @@ or
 ```
 set ledstrip_grb_rgb = GRB
 ```
+or
+
+```
+set ledstrip_grb_rgb = GRBW
+```
 
 Then confirm the required setting by simply setting an LED to be green. If it lights up red, you have the wrong setting.
+Afterwards check if the second LED also lights up red - if not, you might have 4-color SK6812 LEDs and would have to select GRBW.
 
 ## Connections
 

src/main/cli/settings.c

@@ -366,7 +366,7 @@ static const char * const lookupOverclock[] = {
 
 #ifdef USE_LED_STRIP
     static const char * const lookupLedStripFormatRGB[] = {
-        "GRB", "RGB"
+        "GRB", "RGB", "GRBW"
     };
 #endif
 

src/main/drivers/light_ws2811strip.c

@@ -31,6 +31,7 @@
 #include <string.h>
 
 #include "platform.h"
+#include "common/maths.h"
 
 #ifdef USE_LED_STRIP
 
@@ -139,8 +140,8 @@ void ws2811LedStripEnable(void)
 
         const hsvColor_t hsv_black = { 0, 0, 0 };
         setStripColor(&hsv_black);
-        // RGB or GRB ordering doesn't matter for black
-        ws2811UpdateStrip(LED_RGB, 100);
+        // RGB or GRB ordering doesn't matter for black, use 4-channel LED configuraton to make sure all channels are zero
+        ws2811UpdateStrip(LED_GRBW, 100);
 
         ws2811Initialised = true;
     }
@@ -153,23 +154,34 @@ bool isWS2811LedStripReady(void)
 
 STATIC_UNIT_TESTED void updateLEDDMABuffer(ledStripFormatRGB_e ledFormat, rgbColor24bpp_t *color, unsigned ledIndex)
 {
-
+    uint32_t bits_per_led;
     uint32_t packed_colour;
 
     switch (ledFormat) {
         case LED_RGB: // WS2811 drivers use RGB format
             packed_colour = (color->rgb.r << 16) | (color->rgb.g << 8) | (color->rgb.b);
+            bits_per_led = 24;
+            break;
+
+        case LED_GRBW: // SK6812 drivers use this
+        {
+            /* reconstruct white channel from RGB, making the intensity a bit nonlinear, but thats fine for this use case */
+            uint8_t white = MIN(MIN(color->rgb.r, color->rgb.g), color->rgb.b);
+            packed_colour = (color->rgb.g << 24) | (color->rgb.r << 16) | (color->rgb.b << 8) | (white);
+            bits_per_led = 32;
             break;
+        }
 
         case LED_GRB: // WS2812 drivers use GRB format
         default:
             packed_colour = (color->rgb.g << 16) | (color->rgb.r << 8) | (color->rgb.b);
+            bits_per_led = 24;
         break;
     }
 
     unsigned dmaBufferOffset = 0;
-    for (int index = 23; index >= 0; index--) {
-        ledStripDMABuffer[ledIndex * WS2811_BITS_PER_LED + dmaBufferOffset++] = (packed_colour & (1 << index)) ? BIT_COMPARE_1 : BIT_COMPARE_0;
+    for (int index = bits_per_led-1; index >= 0; index--) {
+        ledStripDMABuffer[ledIndex * bits_per_led + dmaBufferOffset++] = (packed_colour & (1 << index)) ? BIT_COMPARE_1 : BIT_COMPARE_0;
     }
 }
 

src/main/drivers/light_ws2811strip.h

@@ -26,19 +26,19 @@
 
 #define WS2811_LED_STRIP_LENGTH    32
 
-#define WS2811_BITS_PER_LED        24
+#define WS2811_BITS_PER_LED_MAX    32
 
 #if defined(USE_WS2811_SINGLE_COLOUR)
 #define WS2811_DATA_BUFFER_SIZE    1
-#define WS2811_DMA_BUFFER_SIZE     (WS2811_DATA_BUFFER_SIZE * WS2811_BITS_PER_LED)
+#define WS2811_DMA_BUFFER_SIZE     (WS2811_DATA_BUFFER_SIZE * WS2811_BITS_PER_LED_MAX)
 // Do 2 extra iterations of the DMA transfer with the output set to low to generate the > 50us delay.
 #define WS2811_DELAY_ITERATIONS    2
 #else
 #define WS2811_DATA_BUFFER_SIZE    WS2811_LED_STRIP_LENGTH
 // for 50us delay
 #define WS2811_DELAY_BUFFER_LENGTH 42
 // number of bytes needed is #LEDs * 24 bytes + 42 trailing bytes)
-#define WS2811_DMA_BUFFER_SIZE     (WS2811_DATA_BUFFER_SIZE * WS2811_BITS_PER_LED + WS2811_DELAY_BUFFER_LENGTH)
+#define WS2811_DMA_BUFFER_SIZE     (WS2811_DATA_BUFFER_SIZE * WS2811_BITS_PER_LED_MAX + WS2811_DELAY_BUFFER_LENGTH)
 #endif
 
 #ifdef USE_LEDSTRIP_CACHE_MGMT
@@ -64,7 +64,8 @@ extern uint32_t ledStripDMABuffer[WS2811_DMA_BUFFER_SIZE];
 // Enumeration to match the string options defined in lookupLedStripFormatRGB in settings.c
 typedef enum {
     LED_GRB,
-    LED_RGB
+    LED_RGB,
+    LED_GRBW
 } ledStripFormatRGB_e;
 
 void ws2811LedStripInit(ioTag_t ioTag);