Add new WS281x driver

Add a new WS281x driver which is a wrapper around jgarff's ws281x library which
works on Pi B+, Pi 2, Pi Zero and probably Pi 3 as well.

jgarff's ws281x library is included as a submodule


Former-commit-id: e473dfd36d31b14598da5e56e4b8bf9f2aa7bb24

libsrc/leddevice/LedDeviceWS281x.cpp

@@ -0,0 +1,78 @@
+#include <iostream>
+
+#include "LedDeviceWS281x.h"
+
+// Constructor
+LedDeviceWS281x::LedDeviceWS281x(const int gpio, const int leds, const uint32_t freq, const int dmanum)
+{
+	initialized = false;
+	led_string.freq = freq;
+	led_string.dmanum = dmanum;
+	led_string.channel[0].gpionum = gpio;
+	led_string.channel[0].invert = 0;
+	led_string.channel[0].count = leds;
+	led_string.channel[0].brightness = 255;
+	led_string.channel[0].strip_type = WS2811_STRIP_RGB;
+
+	led_string.channel[1].gpionum = 0;
+	led_string.channel[1].invert = 0;
+	led_string.channel[1].count = 0;
+	led_string.channel[1].brightness = 0;
+	led_string.channel[0].strip_type = WS2811_STRIP_RGB;
+	if (ws2811_init(&led_string) < 0) {
+		std::cout << "Unable to initialize ws281x library." << std::endl;
+		throw -1;
+	}
+	initialized = true;
+}
+
+// Send new values down the LED chain
+int LedDeviceWS281x::write(const std::vector<ColorRgb> &ledValues)
+{
+	if (!initialized)
+		return -1;
+
+	int idx = 0;
+	for (const ColorRgb& color : ledValues)
+	{
+		if (idx >= led_string.channel[0].count)
+			break;
+		led_string.channel[0].leds[idx++] = ((uint32_t)color.red << 16) + ((uint32_t)color.green << 8) + color.blue;
+	}
+	while (idx < led_string.channel[0].count)
+		led_string.channel[0].leds[idx++] = 0;
+
+	if (ws2811_render(&led_string))
+		return -1;
+
+	return 0;
+}
+
+// Turn off the LEDs by sending 000000's
+// TODO Allow optional power switch out another gpio, if this code handles it can
+// make it more likely we don't accidentally drive data into an off strip
+int LedDeviceWS281x::switchOff()
+{
+	if (!initialized)
+		return -1;
+
+	int idx = 0;
+	while (idx < led_string.channel[0].count)
+		led_string.channel[0].leds[idx++] = 0;
+
+	if (ws2811_render(&led_string))
+		return -1;
+
+	return 0;
+}
+
+// Destructor
+LedDeviceWS281x::~LedDeviceWS281x()
+{
+	if (initialized)
+	{
+		std::cout << "Shutdown WS281x PWM and DMA channel" << std::endl;
+		ws2811_fini(&led_string);
+	}
+	initialized = false;
+}