ESP32 Forum

Posted: **Tue Apr 09, 2019 3:48 pm**

So I am reading the documentation of WS2812B and see that sometimes they list different timing values f.ex.
T0H - 4us and 0.35us in othes docs T0L/T1H - 0.8/0.85us and 0.9us.
I am not sure what's going on and how those leds are properly controlled with what timings?
Are there some min/max values or discrepancy error? Maybe it all depends on manufacturer?
How accurate those times must be?
Can somebody maybe explain and help?
Thanks

Posted: **Wed Apr 10, 2019 1:57 am**

Not sure but there are several drivers on GitHub that use RMT or i2s to achieve high performance and accurate timing

Posted: **Wed Apr 10, 2019 3:19 am**

So I just investigated all those timings a little and I am able to use a simple SPI to fully control WS2812B 32*8 led matrix.
It is very simple and it seems like those timings are based on 1:4 ratio to 'lowest 0 high' )
Therefore 1 rgb bit of led is half a byte so one full rgb pixel is 12bytes - still good performance at 2.86Mhz.
1,000,000 / 0.35us (per specs) = 2,857,142.8571428571428571428571429 ~ 2.86Mhz
I will investigate more but code is so short and much more convenient that RMT which takes more memory too.

Posted: **Sun Apr 14, 2019 1:49 am**

I managed to display RGB full color bitmap from PC - actually a 8x32pixels chunk.
However the picture looks very very bright - seems like colors need calibration - I think it is contrast and saturation.
I must check that later
Here is the code that may help to experiment with SPI and WS281B matrix:

Code: [Select all] [Expand/Collapse]

spi_bus_config_t buscfg={
        .flags              = SPICOMMON_BUSFLAG_MASTER | SPICOMMON_BUSFLAG_MOSI | SPICOMMON_BUSFLAG_SCLK,
        .miso_io_num        = -1,
        .mosi_io_num        = PIN_NUM_MOSI,
        .sclk_io_num        = PIN_NUM_CLK, // - not used !
        .quadwp_io_num      = -1,
        .quadhd_io_num      = -1,
        .max_transfer_sz    = 0
    };
 
    spi_device_interface_config_t devcfg={
        .clock_speed_hz =   2.86*1000*1000, // 1,000,000 / 0.35us ( 2,857,142.857142... ~ 2.86Mhz) 
        .mode           =   0,
        .spics_io_num   =   -1,
        .duty_cycle_pos = 255,
        .queue_size     = 1,
        .pre_cb         = 0,
        .flags          = 0
    };
 
    ESP_ERROR_CHECK( spi_bus_initialize(HSPI_HOST, &buscfg, 1) );
    ESP_ERROR_CHECK( spi_bus_add_device(HSPI_HOST, &devcfg, &spi) );

GeSHi © Codebox Plus Extension

Transmission code:

Code: [Select all] [Expand/Collapse]

 
    const int stride=DISPLAY_WIDTH*3;
    const int n_block_size = DISPLAY_WIDTH*DISPLAY_HEIGHT*3;
 
    static uint8_t* data = NULL;
    static uint8_t* pixels = NULL;
    static spi_transaction_t t =
    {
        .addr       = 0,
        .cmd        = 0,
        .flags      = 0,
        .length     = 0,
        .rxlength   = 0,
        .user       = NULL,
        .rx_buffer  = NULL,
        .tx_buffer  = NULL
    };
    
    if(data==NULL) data = (uint8_t*)malloc(n_block_size); 
    if(pixels==NULL) pixels = (uint8_t*)malloc(n_block_size*12);
 
   // HERE LOADYOUR RGB BITMAP TO *data BUFFER
 
    t.length=32*8 * 12*8;
    t.tx_buffer=pixels;
 
    int x=0;
    for(int offset=0; offset<stride;)
    {
        for(int row=7; row>=0; row--)
        {
            int n = (row*stride) + offset;
            uint32_t pixel = (((uint32_t)data[n+1])<<16) | (((uint32_t)data[n+2])<<8) | ((uint32_t)data[n]);
 
            // 210 - byte order in data
            // RGB
            // GRB
            for(int k=23; k>0; k-=2)
                pixels[x++] = (((pixel>>(k-1))&1) ? 0x0E : 0x08) | (((pixel>>k)&1) ? 0xE0 : 0x80 );
                //pixels[x++] = (((pixel>>(k-1))&1) ? 0b1110 : 0b1000) | (((pixel>>k)&1) ? 0b11100000 : 0b10000000 );
        }
 
        offset+=3;
 
        for(int row=0; row<8; row++)
        {
            int n = (row*stride) + offset;
            uint32_t pixel = (((uint32_t)data[n+1])<<16) | (((uint32_t)data[n+2])<<8) | ((uint32_t)data[n]);
 
            for(int k=23; k>0; k-=2)
                pixels[x++] = (((pixel>>(k-1))&1) ? 0x0E : 0x08) | (((pixel>>k)&1) ? 0xE0 : 0x80 );
        }
 
        offset+=3;
    }

This is for zigzag 8*32 led matrix (going from 8-down to next 8-up left to right pixels)
It works good but maybe there is some catch with colors. It uses 2 color bits per 1 byte so 12bytes gives a 24bit RGB (GRB) pixel
If anyone experiments - please share the results

ESP32 Forum

WS2812B - timings and accuracy

WS2812B - timings and accuracy

Re: WS2812B - timings and accuracy

Re: WS2812B - timings and accuracy

Re: WS2812B - timings and accuracy