Diff: neopixel.h

Revision:

2:3c3c41774cdf

Child:

3:6f392fcb1d3b

diff -r adbbe3e9f2c5 -r 3c3c41774cdf neopixel.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/neopixel.h	Fri Aug 01 22:17:23 2014 +0000
@@ -0,0 +1,146 @@
+#ifndef NEOPIXEL_H
+#define NEOPIXEL_H
+
+#include <stdint.h>
+#include "mbed.h"
+#include "BurstSPI.h"
+
+namespace neopixel
+{
+
+/** Represent the value of a single pixel.
+ *
+ * Each channel uses the full 8 bits: 0x00 is fully off and 0xff is fully on.
+ */
+struct Pixel {
+    uint8_t red;
+    uint8_t green;
+    uint8_t blue;
+};
+
+/** Control the byte order used by the connected pixels.
+ *
+ * The vast majority of NeoPixels use a GRB byte order, so this is the default.
+ * A few use a RGB byte order.
+ *
+ * In principle, the WS281x controllers could be connected with _any_ byte
+ * ordering, but only GRB and RGB are supported at the moment.
+ */
+enum ByteOrder {
+    BYTE_ORDER_GRB,
+    BYTE_ORDER_RGB,
+};
+
+typedef void (*PixelGenerator)(Pixel* out, uint32_t index, uintptr_t extra);
+
+/** Control an array or chain of NeoPixel-compatible RGB LEDs.
+ *
+ * "NeoPixel" is Adafruit's name for WS2812- and WS2811-based addressable RGB
+ * LEDs. This library should work with any WS2811- or WS2812-based devices, as
+ * long as they support the fast-mode (800kHz) interface.
+ *
+ * Most example code uses bit-banging to generate the timed signal precisely.
+ * This library uses an SPI peripheral instead. The main advantage of this is
+ * that the chip can service interrupts and the like without disrupting the
+ * signal (as long as the interrupts don't take _too_ long). The main
+ * disadvantage is that it requires the use of an SPI peripheral.
+ *
+ * @note SPI peripherals will tend to leave the output pin ('MOSI') floating
+ * after a packet is sent. This will confuse the connected pixels, which expect
+ * the line to be driven low when idle. One way to fix this is to add a 10k
+ * resistor between 'MOSI' and ground so that it drops to '0' when not driven.
+ * Another method is to enable the on-chip pull-down resistor on the output pin.
+ * However, the mbed API only exposes this function through the DigitalIn and
+ * DigitalInOut classes. If you want to use the on-chip pull-down, you'll have
+ * to temporarily connect a DigitalIn peripheral _before_ creating instantiating
+ * the PixelArray.
+ *
+ * @code
+ * // Sample generator: Cycle through each colour combination, increasing the
+ * // brightness each time. `extra` is used as an iteration counter.
+ * void generate(neopixel::Pixel * out, uint32_t index, uintptr_t extra) {
+ *   uint32_t brightness = (index + extra) >> 3;
+ *   out->red   = ((index + extra) & 0x1) ? brightness : 0;
+ *   out->green = ((index + extra) & 0x2) ? brightness : 0;
+ *   out->blue  = ((index + extra) & 0x4) ? brightness : 0;
+ * }
+ *
+ * int main() {
+ *   // Create a temporary DigitalIn so we can configure the pull-down resistor.
+ *   // (The mbed API doesn't provide any other way to do this.)
+ *   // An alternative is to connect an external pull-down resistor.
+ *   DigitalIn(p5, PullDown);
+ *
+ *   // The pixel array control class.
+ *   neopixel::PixelArray array(p5);
+ *
+ *   uint32_t offset = 0;
+ *   while (1) {
+ *     array.update(generate, 100, offset++);
+ *     wait_ms(250);
+ *   }
+ * }
+ * @endcode
+ */
+class PixelArray
+{
+public:
+    /** Initialize a PixelArray.
+     *
+     * @param out Output (SPI MOSI) pin.
+     * @param byte_order The order in which to transmit colour channels.
+     */
+    PixelArray(PinName out,
+               ByteOrder byte_order = BYTE_ORDER_GRB);
+
+    /** Update the pixel display from a buffer.
+     *
+     * This update method is good in the following situations:
+     * - You want to make incremental changes to a fixed frame pattern.
+     * - The frame is hard (or impossible) to generate procedurally.
+     * - The frame requires a lot of time to generate.
+     *
+     * @param buffer Pixel data to be written.
+     * @param length The number of pixels to write.
+     *
+     * buffer[0] is written to the pixel nearest the mbed.
+     * buffer[length-1] is written to the pixel furthest from the mbed.
+     */
+    void update(Pixel buffer[], uint32_t length);
+
+    /** Update a pixel chain using the callback to generate the value for each
+     * pixel.
+     *
+     * This update method is good in the following situations:
+     * - You have a lot of pixels to drive and don't have enough RAM to buffer
+     *   them all.
+     * - You want to display a frame pattern that can be generated procedurally
+     *   generated without intensive processing.
+     *
+     * @param generator A callback which is called to generate a value for each
+     * pixel on demand. This function must be fairly fast: if it takes more
+     * than about 8-9us, the interface will reset and the display will be
+     * corrupted. The exact time limits will vary between WS281x variants. As a
+     * rough guide, an LPC1768 at 96MHz can (conservatively) execute about 750
+     * instructions in that time.
+     *
+     * @param length The number of pixels to write.
+     *
+     * @param extra An arbitrary value to pass into the generator function. For
+     * example, this is a good way to pass an animation time index to the
+     * generator function.
+     */
+    void update(PixelGenerator generator, uint32_t length, uintptr_t extra);
+
+private:
+    BurstSPI spi_;
+    ByteOrder byte_order_;
+    
+    static int const latch_time_us_ = 50;
+    
+    void send_pixel(Pixel& pixel);
+};
+
+}
+
+#endif
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