Brian Daniels / WS2812

Library for the WS2812 LED Driver. Uses bit banging and nops for precise timing. Number of nops executed are configurable at run time.

Dependents:   WS2812_Example WS2812_Example_fade Lamp_03 Lamp_04 ... more

This library uses bit banging to control the LED strip. Because the mbed platform doesn't have a timer standardized that doesn't have a resolution lower a microsecond, we have to use NOPs. Also, the time it takes to toggle a GPIO pin is not consistent across platforms and it does not correlate to the system clock in any way. It is completely dependent on the platform's implementation.

I have a found the timings for a few boards. They are currently listed on the example program page below.

Import programWS2812_Example

Example for WS2812 Library

Last commit 12 Feb 2015 by Brian Daniels

When using this on a new platform, you'll need to use a logic analyzer to determine the timings.

/media/uploads/bridadan/k64f_ws2812_timing_v2.png

Above is a screenshot from a Saleae logic analyzer. You'll notice that the "1" pulse is longer than the "0" pulse. The "Data low" pulses should be consistent. The timing requirements for these pulses can be found below (Source: http://wp.josh.com/2014/05/13/ws2812-neopixels-are-not-so-finicky-once-you-get-to-know-them/).

/media/uploads/bridadan/ws2812_timings.png

If you find timings for a new board you're using, please PM me or start a discussion below and I'll add it to this page!

For more on the timings and data format of the WS2812 drivers, you should read the datasheet and the article "NeoPixels Revealed: How to (not need to) generate precisely timed signals" listed below.

References:

WS2812B Datasheet: https://www.adafruit.com/datasheets/WS2812B.pdf

"NeoPixels Revealed: How to (not need to) generate precisely timed signals": http://wp.josh.com/2014/05/13/ws2812-neopixels-are-not-so-finicky-once-you-get-to-know-them/

Diff: WS2812.cpp

Revision:
1:aadbf08c62a2
Parent:
0:0b79cafcb387
diff -r 0b79cafcb387 -r aadbf08c62a2 WS2812.cpp
--- a/WS2812.cpp	Thu Feb 12 19:17:10 2015 +0000
+++ b/WS2812.cpp	Thu Feb 12 20:20:10 2015 +0000
@@ -1,15 +1,15 @@
 #include "WS2812.h"
 
-WS2812::WS2812(PinName d, int size) : __gpo(d)
+WS2812::WS2812(PinName pin, int size, int zeroHigh, int zeroLow, int oneHigh, int oneLow) : __gpo(pin)
 {
     __size = size;
     __transmitBuf = new bool[size * FRAME_SIZE];
-    __use_II = 0; // 0=off,1=use global,2=per pixel
+    __use_II = OFF;
     __II = 0xFF; // set global intensity to full
-    __outPin = d;
+    __outPin = pin;
     
     // Default values designed for K64f. Assumes GPIO toggle takes ~0.4us
-    setDelays(0, 5, 5, 0);
+    setDelays(zeroHigh, zeroLow, oneHigh, oneLow);
 }
 
 
@@ -47,10 +47,10 @@
         agrb[2] = color  & 0x000000FF;
         agrb[3] = (color & 0xFF000000) >> 24;
     
-        // set and intensity scaling factor (global, per pixel, none)
-        if (__use_II == 1) {
+        // set the intensity scaling factor (global, per pixel, none)
+        if (__use_II == GLOBAL) {
             sf = __II;
-        } else if (__use_II == 2) {
+        } else if (__use_II == PER_PIXEL) {
             sf = agrb[3];
         } else {
             sf = 0xFF;
@@ -80,8 +80,13 @@
 void WS2812::write_offsets (int buf[],int r_offset, int g_offset, int b_offset) {
     int i, j;
     
+    // Load the transmit buffer
     __loadBuf(buf, r_offset, g_offset, b_offset);
 
+    // Entering timing critical section, so disabling interrupts
+    __disable_irq();
+    
+    // Begin bit-banging
     for (i = 0; i < FRAME_SIZE * __size; i++) {
         j = 0;
         if (__transmitBuf[i]){
@@ -104,15 +109,18 @@
             }
         }
     }
+    
+    // Exiting timing critical section, so enabling interrutps
+    __enable_irq();
 }
 
 
-void WS2812::useII(int d)
+void WS2812::useII(BrightnessControl bc)
 {
-    if (d > 0) {
-        __use_II = d;
+    if (bc > OFF) {
+        __use_II = bc;
     } else {
-        __use_II = 0;
+        __use_II = OFF;
     }
 }