furnace/doc/7-systems/fds.md

Famicom Disk System

the Famicom Disk System is an expansion device for the Famicom (known as NES outside Japan), a popular console from the '80's. as it name implies, it allowed people to play games on specialized floppy disks that could be rewritten on vending machines, therefore reducing the cost of ownership and manufacturing.

it also offers an additional 6-bit, 64-byte wavetable sound channel with (somewhat limited) FM capabilities, which is what Furnace supports.

effects

• 10xx: change wave.
• 11xx: set modulation depth.
• 12xy: set modulation speed high byte and toggle on/off.
  • x is the toggle. a value of 1 turns on the modulator.
  • y is the speed.
• 13xx: set modulation speed low byte.
• 14xx: set modulator position.
• 15xx: set modulator wave.
  • xx points to a wavetable. it should (preferably) have a height of 7 with the values mapping to:
    • 0: +0
    • 1: +1
    • 2: +2
    • 3: +3
    • 4: reset
    • 5: -3
    • 6: -2
    • 7: -1
  • why is this mapping so unnatural? because that's how DefleMask does it (yeah, as you may have guessed this effect is mostly for compatibility reasons)...