Software Serial on Attiny84

Which of the two timers does Software Serial use on Attiny84? I am working on using interrupts. Anyone know of interrupt timers libraries for the Attinys?

Let's read the code and find out!

https://github.com/arduino/Arduino/blob/master/hardware/arduino/avr/libraries/SoftwareSerial/SoftwareSerial.cpp

I see nothing that resembles using a timer there - do you?

I suppose not. I assumed the serial communication used a timer to synchronize data. If it doesn't use a timer, what does it use?

Thanks for your help!

Lafred:
I suppose not. I assumed the serial communication used a timer to synchronize data. If it doesn't use a timer, what does it use?

Thanks for your help!

The CPU clock. Parts where they explain it in comments start on line 302.

(btw, might I suggest the 841? It's only a few cents more expensive than the 84, and has 2 hardware serials! And 6 PWM channels! See link in sig for core)