MSPM0SpiPixelStrip.hxx

Go to the documentation of this file.

 
#ifndef _FREERTOS_DRIVERS_TI_MSPM0PIXELSTRIP_HXX_
#define _FREERTOS_DRIVERS_TI_MSPM0PIXELSTRIP_HXX_
 
#include <stdint.h>
#include <ti/devices/msp/msp.h>
#include <ti/driverlib/driverlib.h>
 
class SpiPixelStrip
{
public:
    SpiPixelStrip(SPI_Regs *spi, unsigned num_pixels, uint8_t *backing_data)
        : spi_(spi)
        , numPixels_(num_pixels)
        , data_(backing_data)
    { }
 
    void hw_init();
 
    void update_sync()
    {
        clear_iteration();
        while (!eof())
        {
            uint16_t next_word = 0;
            uint16_t ofs = 1u;
            // Computes 16 SPI bits with 5 pulses.
            while (!eof() && ofs < (1u << 13))
            {
                // Appends an 110 or 100 depending opn what the next bit should
                // be.
                next_word |= ofs;
                ofs <<= 1;
                if (next_bit())
                    next_word |= ofs;
                ofs <<= 2;
            }
            // We leave an extra bit as zero at the end of the word. We hope
            // that this will not confuse the pixel. They care mostly about the
            // length of the HIGH pulse.
            DL_SPI_transmitDataBlocking16(spi_, next_word);
            // Note that there is no wait here for the transfer to complete.
            // This is super important, because we want to be computing the next
            // word while the previous word is emitted by SPI.
        }
        // The last bit output is a zero, and leaving the line there is
        // reasonable, because it matches the latch level.
    }
 
private:
    void clear_iteration()
    {
        currentByte_ = 0;
        nextBit_ = 0x80;
    }
    bool next_bit()
    {
        bool ret = data_[currentByte_] & nextBit_;
        nextBit_ >>= 1;
        if (!nextBit_)
        {
            nextBit_ = 0x80;
            currentByte_++;
        }
        return ret;
    }
    bool eof()
    {
        return currentByte_ >= numPixels_ * 3;
    }
 
    SPI_Regs *spi_;
    unsigned numPixels_;
    uint8_t *data_;
 
    unsigned currentByte_;
    uint8_t nextBit_;
};
 
#endif // _FREERTOS_DRIVERS_TI_MSPM0PIXELSTRIP_HXX_