Sounds to me like you should've started the 'project' for 'UNI' earlier...or maybe get a bit of help from the 'INSTRUCTOR' (if that's what they call them these days...I call them placeholders) or maybe even try some of your CLASSMATES.
Use another pin to trigger your 'PORTB.4' pin, write code to trigger that pin to trigger the other pin.
And no, I don't think this will solve your problem. If GOSUB'ing into your interrupt routine is slow, why would triggering an interrupt to go to the interrupt routine work any better? Your program is most likely hanging up in a loop somewhere or something similar making you think that it's not reacting fast enough, whereas triggering an interrupt in hardware may actually jump directly to that code.
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