Anirudh Bisht / PixelArray

Main Error

Dependencies:   BurstSPI

Fork of PixelArray by Jacob Bramley

neopixel-spi.cpp@1:adbbe3e9f2c5, 2014-07-25 (annotated)

Committer:
JacobBramley
Date:
Fri Jul 25 15:18:03 2014 +0000
Revision:
1:adbbe3e9f2c5
Parent:
0:38eeab21a162 
First, tentative release. This version hasn't been tested (except to check that it builds) because I don't have any NeoPixels.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
JacobBramley 0:38eeab21a162 1 #include <stdint.h>
JacobBramley 0:38eeab21a162 2 #include "mbed.h"
JacobBramley 0:38eeab21a162 3 #include "neopixel-spi.h"
JacobBramley 0:38eeab21a162 4
JacobBramley 0:38eeab21a162 5 namespace neopixel {
JacobBramley 0:38eeab21a162 6
JacobBramley 0:38eeab21a162 7 Array::Array(PinName out) : spi_(out, NC, NC) {
JacobBramley 0:38eeab21a162 8 // TODO: WS2811 has a different timing specification.
JacobBramley 0:38eeab21a162 9
JacobBramley 0:38eeab21a162 10 // WS2812 bit timings:
JacobBramley 0:38eeab21a162 11 // '0': ----________ mark: 0.40us, space: 0.85us
JacobBramley 0:38eeab21a162 12 // '1': --------____ mark: 0.80us, space: 0.45us
JacobBramley 0:38eeab21a162 13 // The period is 1.25us, giving a basic frequency of 800kHz.
JacobBramley 0:38eeab21a162 14 // Using three SPI bits per NeoPixel bit, we need an API frequency of 2.4MHz.
JacobBramley 0:38eeab21a162 15 // '0': 100 mark: 0.42us, space: 0.83us
JacobBramley 0:38eeab21a162 16 // '1': 110 mark: 0.83us, space: 0.42us
JacobBramley 0:38eeab21a162 17 // These timings are well within the +/-150ns tolerance specified by WS2812.
JacobBramley 0:38eeab21a162 18
JacobBramley 0:38eeab21a162 19 spi_.frequency(2400000);
JacobBramley 0:38eeab21a162 20 spi_.format(12); // Send four NeoPixel bits in each packet.
JacobBramley 0:38eeab21a162 21 }
JacobBramley 0:38eeab21a162 22
JacobBramley 0:38eeab21a162 23 static void SendFourBits(BurstSPI& spi, uint32_t bits) {
JacobBramley 0:38eeab21a162 24 static int const pattern_width = 3;
JacobBramley 0:38eeab21a162 25 uint32_t word = 04444; // 0b100100100100
JacobBramley 0:38eeab21a162 26
JacobBramley 0:38eeab21a162 27 for (int i = 0; i < 4; i++) {
JacobBramley 0:38eeab21a162 28 word |= ((bits >> 3) & 1) << (pattern_width * i + 1);
JacobBramley 0:38eeab21a162 29 }
JacobBramley 0:38eeab21a162 30
JacobBramley 0:38eeab21a162 31 spi.fastWrite(word);
JacobBramley 0:38eeab21a162 32 }
JacobBramley 0:38eeab21a162 33
JacobBramley 0:38eeab21a162 34 void Array::Update(Pixel buffer[], size_t length) {
JacobBramley 0:38eeab21a162 35 // Pixels are sent as follows:
JacobBramley 0:38eeab21a162 36 // - The first transmitted pixel is the pixel closest to the transmitter.
JacobBramley 0:38eeab21a162 37 // - The most significant bit is always sent first.
JacobBramley 0:38eeab21a162 38 // - Green is sent first, then red, then blue.
JacobBramley 0:38eeab21a162 39 //
JacobBramley 0:38eeab21a162 40 // g7,g6,g5,g4,g3,g2,g1,g0,r7,r6,r5,r4,r3,r2,r1,r0,b7,b6,b5,b4,b3,b2,b1,b0
JacobBramley 1:adbbe3e9f2c5 41 // \_____________________________________________________________________/
JacobBramley 1:adbbe3e9f2c5 42 // | _________________...
JacobBramley 1:adbbe3e9f2c5 43 // | / __________________...
JacobBramley 1:adbbe3e9f2c5 44 // | / / ___________________...
JacobBramley 1:adbbe3e9f2c5 45 // | / / /
JacobBramley 0:38eeab21a162 46 // GRB,GRB,GRB,GRB,...
JacobBramley 0:38eeab21a162 47
JacobBramley 0:38eeab21a162 48 for (size_t i = 0; i < length; i++) {
JacobBramley 0:38eeab21a162 49 SendFourBits(spi_, (buffer[i].green >> 4) & 0xf);
JacobBramley 0:38eeab21a162 50 SendFourBits(spi_, (buffer[i].green >> 0) & 0xf);
JacobBramley 0:38eeab21a162 51 SendFourBits(spi_, (buffer[i].red >> 4) & 0xf);
JacobBramley 0:38eeab21a162 52 SendFourBits(spi_, (buffer[i].red >> 0) & 0xf);
JacobBramley 0:38eeab21a162 53 SendFourBits(spi_, (buffer[i].blue >> 4) & 0xf);
JacobBramley 0:38eeab21a162 54 SendFourBits(spi_, (buffer[i].blue >> 0) & 0xf);
JacobBramley 0:38eeab21a162 55 }
JacobBramley 0:38eeab21a162 56 spi_.clearRX();
JacobBramley 0:38eeab21a162 57
JacobBramley 0:38eeab21a162 58 wait_us(50);
JacobBramley 0:38eeab21a162 59 }
JacobBramley 0:38eeab21a162 60
JacobBramley 0:38eeab21a162 61 }