Trackball

Special controller only used in The Irritating Maze cabs.

Works the same way as an upside-down mechanical mouse. Uses two optical encoders for X and Y movement, handled by the SIT board.

A special system ROM is used (236-bios.sp1).

The counter values are read from REG_P1CNT:

• The X counter value when bit 0 of REG_POUTPUT is 0.
• The Y counter value when bit 0 of REG_POUTPUT is 1.

Speed and direction are computed from the counter deltas.