This repo contains the source code needed to make the attiny85 glow a led with a fire effect as seen on my blog: http://simodax.github.io/2016/07/31/thresh-statue-flame-effect-attiny85.html
As light intensities are random (to emulate the fire effect) I seeded the rng with random electrical noise picked up by analog pin 2.
You can check the full documentation of the microcontroller here: http://www.atmel.com/Images/Atmel-2586-AVR-8-bit-Microcontroller-ATtiny25-ATtiny45-ATtiny85_Datasheet.pdf