just spent a day trying to get interrupts working without interfering with 5110 lcd updates
the adafruit library was taking 80ms to update the display the first time, and my spare hardware timers were unable to time slower than that for triggering an overflow interrupt to count system time
then i tried other libraries, some of which were far faster, but all of them had the display upside-down and couldn't flip it, unlike the adafruit library
then i realised it was because the adafruit library was building a software buffer, rotating it, and then sending that to the display
i briefly flirted with the idea of generating an upside-down font and queuing the characters to be written backwards as the cursor still advances in the wrong direction
ultimately i gave up and redesigned the housing to have the lcd the intended orientation

cmon, don't they look better with a fat chin than with a fat forehead?