AVR-Chat

On a mega48, I am trying to generate a external interrupt in the 
software by writing:
    sbi EIFR, INTF0     ; simulate a step in test mode by setting INT0 
flag (step input)

But this doesn't seem to work  -- neither in the simulator nor on real 
hardware.

I am 99% sure INT0 is set up properly because the interrupt vector 
executes if a falling edge is applied to the pin.

Is my method of generating an external interrupt in software valid, or 
am I missing something?

Aaron