David Johnson-Davies build a OLED display function plotter based on ATtiny85 microcontroller. He writes:
This project describes a simple routine for plotting a function on a 128×64 I2C OLED graphics display. Unlike most Arduino graphics libraries this routine doesn’t require a RAM buffer, and so will work on any processor down to an ATtiny85:
The routine will work on monochrome 128×64 I2C OLED displays based on either the SSD1306 driver, such as the display available from Adafruit, or the SH1106 driver, used in displays available from Chinese suppliers.
Tiny Function Plotter using ATtiny85 – [Link]