Arkanoid pad

The Arkanoid pad is a controller with 1 button and a dial (similar to a rotating volume knob on an old radio), used by at least Arkanoid and Arkanoid Revenge of Doh. This implementation is mostly based on guesswork, and has only been tested with Arkanoid 1.

PSG R14 bits 0 and 1 are used, bits 2-5 are set to 1.
Button state is easy: bit 1 of PSG R14, 0 when pressed, 1 when not pressed.
Dial state is on a 9 bit shift register. A positive edge (0 --> 1) on PSG R15 bit 4 puts the current dial position (164 is far left, 236 is middle, 309 is far right) into the shift register. Reading PSG R14 bit 0 returns the current bit, starting with bit 8. The shift register is shifted by a positive edge on PSG R15 bit 0.

As an example, to read the dial position:
reset R15 bit 4
set R15 bit 4
read R14 bit 0 (returns dial bit 8)
reset R15 bit 0
set R15 bit 0
read R14 bit 0 (returns dial bit 7)
etc.

On port 2, the strobe bits are probably 5 and 1.