Reading CDDA sound levels

Registers and  hold the values of the currently streamed CD audio data, in a reversed 16bit 2's complement format suited for the LC78815 DAC. They were only used to display the vu-meters in the CD player interface.

The CD system ROM uses the following code to reverse the bits:

It reads both registers multiple times during each frame (every 16 raster lines, by using the raster interrupt) to get an average value.

Demo
This does NOT work on current emulators.

Uses:
 * Raster line interrupts
 * Sprites (shrink and displacement)
 * Fix (frame counter)
 * Palettes

Source for AS and iso image:

[Youtube video]