USI-based TWI (I2C) slave driver for ATtiny microcontrollers
This driver is for Microchip (ex Atmel) ATtiny devices that implement the I2C protocol by using the Universal Serial Interface (USI) peripheral, that is, microcontrollers that are not equipped with I2C-specific hardware.
This version is for standard I2C applications that can use the microcontroller interrupt vectors. For special applications, such as bootloaders and the like, it is recommended to use a version that does not use interrupts.