Put together an implementation. Works good on my hardware. Here were the required changes
dinput
������ - always DIERR_ACQUIRED if trying to set autocenter������and acquired
������ - send a stop to all effects on acquire if autocenter is off
bus{sdl,udev}
������ - enable autocenter������on reset
������ - disable autocenter������on stop all effects
The prior code didn't DIERR_ACQUIRED if it was in exclusive mode, but Windows does. This behaviour is what makes it easy to implement as it means you only have to deal with������autocenter during an acquire������where you can just do a stop all effects as only autocenter is running.