Understood and hooked up sound HW in Little Robin, that is a weird combination of 2 DAC sound chips, the video scanline register, interrupt generation (irq lv 4 with an input port that defines the kind of irq, currently hooked up with the video frame number) and two lovely 16-bit port registers (one for each DAC) that alternates the resulting 8-bit sound index according to an external source (frame number % 16 with current implementation, as each “sound irq” happens every 8 frames). And by alternation it means in the sense of muxing between LSB or MSB of the aforementioned sound index (that is obviously pointless if isn’t a form of protection).