From 1bff517adf624648c71fabbe8e8302ecbf235802 Mon Sep 17 00:00:00 2001
From: penfold42 <penfold42@users.noreply.github.com>
Date: Sun, 14 May 2017 03:09:26 +1000
Subject: [PATCH] Ammeded timing to suit new revision of ws2812c (#439)

Should also work with WS2813 (but untested)

Included comments on the timing calculations
---
 libsrc/leddevice/LedDeviceWs2812SPI.cpp | 47 +++++++++++++++++++++----
 libsrc/leddevice/LedDeviceWs2812SPI.h   |  2 ++
 2 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/libsrc/leddevice/LedDeviceWs2812SPI.cpp b/libsrc/leddevice/LedDeviceWs2812SPI.cpp
index b211e56d..b98db68f 100644
--- a/libsrc/leddevice/LedDeviceWs2812SPI.cpp
+++ b/libsrc/leddevice/LedDeviceWs2812SPI.cpp
@@ -1,8 +1,43 @@
 #include "LedDeviceWs2812SPI.h"
 
+/*
+From the data sheet:
+
+(TH+TL=1.25μs±600ns)
+
+T0H,	 0 code, high level time,	 0.40µs ±0.150ns
+T0L,	 0 code, low level time,	 0.85µs ±0.150ns
+T1H,	 1 code, high level time,	 0.80µs ±0.150ns
+T1L,	 1 code, low level time,	 0.45µs ±0.150ns
+WT,	 Wait for the processing time,	 NA
+Trst,	 Reset code,low level time,	 50µs (not anymore... need 300uS for latest revision)
+
+To normalise the pulse times so they fit in 4 SPI bits:
+
+On the assumption that the "low" time doesnt matter much
+
+A SPI bit time of 0.40uS = 2.5 Mbit/sec
+T0 is sent as 1000
+T1 is sent as 1100
+
+With a bit of excel testing, we can work out the maximum and minimum speeds:
+2106000 MIN
+2590500 AVG
+3075000 MAX
+
+Wait time:
+Not Applicable for WS2812
+
+Reset time:
+using the max of 3075000, the bit time is 0.325
+Reset time is 300uS = 923 bits = 116 bytes
+
+*/
+
 LedDeviceWs2812SPI::LedDeviceWs2812SPI(const QJsonObject &deviceConfig)
 	: ProviderSpi()
 	, SPI_BYTES_PER_COLOUR(4)
+	, SPI_FRAME_END_LATCH_BYTES(116)
 	, bitpair_to_byte {
 		0b10001000,
 		0b10001100,
@@ -20,14 +55,13 @@ LedDevice* LedDeviceWs2812SPI::construct(const QJsonObject &deviceConfig)
 
 bool LedDeviceWs2812SPI::init(const QJsonObject &deviceConfig)
 {
-	_baudRate_Hz = 3000000;
+	_baudRate_Hz = 2600000;
 	if ( !ProviderSpi::init(deviceConfig) )
 	{
 		return false;
 	}
-	WarningIf(( _baudRate_Hz < 2050000 || _baudRate_Hz > 4000000 ), _log, "SPI rate %d outside recommended range (2050000 -> 4000000)", _baudRate_Hz);
+	WarningIf(( _baudRate_Hz < 2106000 || _baudRate_Hz > 3075000 ), _log, "SPI rate %d outside recommended range (2106000 -> 3075000)", _baudRate_Hz);
 
-	const int SPI_FRAME_END_LATCH_BYTES = 3;
 	_ledBuffer.resize(_ledRGBCount * SPI_BYTES_PER_COLOUR + SPI_FRAME_END_LATCH_BYTES, 0x00);
 
 	return true;
@@ -52,9 +86,10 @@ int LedDeviceWs2812SPI::write(const std::vector<ColorRgb> &ledValues)
 		spi_ptr += SPI_BYTES_PER_LED;
 	}
 
-	_ledBuffer[spi_ptr++] = 0;
-	_ledBuffer[spi_ptr++] = 0;
-	_ledBuffer[spi_ptr++] = 0;
+	for (int j=0; j < SPI_FRAME_END_LATCH_BYTES; j++)
+	{
+		_ledBuffer[spi_ptr++] = 0;
+	}
 
 	return writeBytes(_ledBuffer.size(), _ledBuffer.data());
 }
diff --git a/libsrc/leddevice/LedDeviceWs2812SPI.h b/libsrc/leddevice/LedDeviceWs2812SPI.h
index b7facf8c..4da3d9fb 100644
--- a/libsrc/leddevice/LedDeviceWs2812SPI.h
+++ b/libsrc/leddevice/LedDeviceWs2812SPI.h
@@ -37,5 +37,7 @@ private:
 
         const int SPI_BYTES_PER_COLOUR;
 
+	const int SPI_FRAME_END_LATCH_BYTES;
+
 	uint8_t bitpair_to_byte[4];
 };