cpldcpu wrote:Can the Attiny 85 do 12 MHz at 3.3V? I am certain this is out of spec.
This is Yoshiyasu Takefuji's project, published in Circuit Cellar in issue no.213, year 2008, using Christian's driver. He arrived at the point (12MHz, 3.3V) by interpolation, I think. Anyway, I would like to draw attention towards the timing matter that I mentioned.
If you clear pending interrupts before the SEI there may be. Otherwise the is most likely an interrupt pending and the ISR is called. You should mention what you are doing before the SEI.
The device has just been plugged into the host port. What I do before the sei() is exactly depicted in the code block of post #1, which is ALL of the main function. I think you know what usbInit() does, do you?