AVR code to communicate with a WS2811 led controller from an AVR clocked from its internal 8Mhz or 9.6Mhz oscillator. A microcontroller like an 8Mhz atmega88, attiny13 or attiny2313 using this code can control a 800kbit WS2811 led string without any additional components. The interesting stuff is in ws2811_8.h, while the assembly code design is documented in a spreadsheet.

A more elaborate description can be found here.