ws2812_i2s: WS2812 leds driver implementation using i2s_dma library

examples/ws2812_i2s/Makefile

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+# Makefile for the ws2812_i2s example
+
+PROGRAM=ws2812_i2s_example
+EXTRA_COMPONENTS = extras/i2s_dma extras/ws2812_i2s
+
+include ../../common.mk

examples/ws2812_i2s/ws2812_i2s_colour_loop.c

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+/**
+ * Example of ws2812_i2s library usage.
+ *
+ * This example shows light that travels in circle with fading tail.
+ * As ws2812_i2s library using hardware I2S the output pin is GPIO3 and
+ * can not be changed.
+ *
+ * This sample code is in the public domain.,
+ */
+#include "espressif/esp_common.h"
+#include "FreeRTOS.h"
+#include "task.h"
+#include "esp/uart.h"
+#include <stdint.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include "ws2812_i2s/ws2812_i2s.h"
+
+const uint32_t led_number = 60;
+const uint32_t tail_fade_factor = 2;
+const uint32_t tail_length = 8;
+
+static void fade_pixel(ws2812_pixel_t *pixel, uint32_t factor)
+{
+    pixel->red = pixel->red / factor;
+    pixel->green = pixel->green / factor;
+    pixel->blue = pixel->blue / factor;
+}
+
+static int fix_index(int index)
+{
+    if (index < 0) {
+        return (int)led_number + index;
+    } else if (index >= led_number) {
+        return index - led_number;
+    } else {
+        return index;
+    }
+}
+
+static ws2812_pixel_t next_colour()
+{
+    ws2812_pixel_t colour = {0, 0, 0};
+    colour.red = rand() % 256;
+    colour.green = rand() % 256;
+    colour.blue = rand() % 256;
+
+    return colour;
+}
+
+static void demo(void *pvParameters)
+{
+    ws2812_pixel_t pixels[led_number];
+    int head_index = 0;
+
+    ws2812_i2s_init(led_number);
+
+    memset(pixels, 0, sizeof(ws2812_pixel_t) * led_number);    
+
+    while (1) {
+        pixels[head_index] = next_colour();
+        for (int i = 0; i < led_number; i++) {
+            head_index = fix_index(head_index + 1);
+            pixels[head_index] = pixels[fix_index(head_index-1)];
+            for (int ii = 1; ii < tail_length; ii++) {
+                fade_pixel(&pixels[fix_index(head_index - ii)], tail_fade_factor);
+            }
+            memset(&pixels[fix_index(head_index - tail_length)], 0, 
+                    sizeof(ws2812_pixel_t));
+
+            ws2812_i2s_update(pixels);
+            vTaskDelay(20 / portTICK_RATE_MS);
+        }
+    }
+}
+
+void user_init(void)
+{
+    uart_set_baud(0, 115200);
+
+    xTaskCreate(&demo, (signed char *)"ws2812_i2s", 256, NULL, 10, NULL);
+}