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Ammeded timing to suit new revision of ws2812c (#439) 

Should also work with WS2813 (but untested)

Included comments on the timing calculations
This commit is contained in:
penfold42 2017-05-14 03:09:26 +10:00 committed by redPanther
parent f3a1a15324
commit 1bff517adf
2 changed files with 43 additions and 6 deletions
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47
libsrc/leddevice/LedDeviceWs2812SPI.cpp
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@ -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());
}

2
libsrc/leddevice/LedDeviceWs2812SPI.h
View File

@ -37,5 +37,7 @@ private:
const int SPI_BYTES_PER_COLOUR;
const int SPI_FRAME_END_LATCH_BYTES;
uint8_t bitpair_to_byte[4];
};