I've never used a HP 9885 floppy disk drive but the chip sounds pretty awesome for PLC programmable logic controller drudgery tasks like emulating many relays for combinatorial logic.
So there's probably a simulated virtual relay that won't let the disk drive heads drop on the media unless the motor is up to speed, or a relay that locks the door if the motor is up to speed or makes kinda a phase locked loop that speeds up and slows down the drive motor until the speed is dead on accurate at 300 rpm. Upon power up or reset drive the head toward track zero until the track zero sensor is hit. A relay that hardware disables the write head if the write protect switch is set. Disable additional stepping of the track stepper motors to prevent damage if the head bonks into the track zero microswitch sensor. All kinds of fun stuff that doesn't involve addition but just piles of combinatorial logic rules repeatedly run thru a couple hundred times a second.
So there's probably a simulated virtual relay that won't let the disk drive heads drop on the media unless the motor is up to speed, or a relay that locks the door if the motor is up to speed or makes kinda a phase locked loop that speeds up and slows down the drive motor until the speed is dead on accurate at 300 rpm. Upon power up or reset drive the head toward track zero until the track zero sensor is hit. A relay that hardware disables the write head if the write protect switch is set. Disable additional stepping of the track stepper motors to prevent damage if the head bonks into the track zero microswitch sensor. All kinds of fun stuff that doesn't involve addition but just piles of combinatorial logic rules repeatedly run thru a couple hundred times a second.