“WS2812 LEDs (‘NeoPixels’) are intelligent devices, that can be programmed to a specific 24-bit red, green & blue (RGB) colour, by a pulse train on a single wire. They are capable of being daisy-chained, so a single pulse line can drive a large number of devices.
The programming pulses have to be accurately timed to within fractions of a microsecond, so conventional Raspberry Pi techniques are of limited use; they can only handle a small number of pulse channels, driving a maximum of 1 or 2 strings of LEDs, which is insufficient for a complex display.
This blog post describes a new technique that uses the RPi Secondary Memory Interface (SMI) to drive 8 or 16 channels with very accurate timing. No additional hardware is needed, apart from a 3.3 to 5V level-shifter, that is required for all NeoPixel interfaces.”