furnace/doc/7-systems/pokey.md

POKEY

a sound and input chip developed by Atari for their 8-bit computers (Atari 400, 800, XL/XE and so on). 4 channels of signature Atari sounds.

effects

• 10xx: set waveform.
  • 0: harsh noise (poly5+17)
  • 1: square buzz (poly5)
  • 2: weird noise (poly4+5)
  • 3: square buzz (poly5)
  • 4: soft noise (poly17)
  • 5: square
  • 6: bass (poly4)
  • 7: buzz (poly4)
• 11xx: set AUDCTL. xx is a bitmask.
  • bit 7: 9-bit poly mode. shortens noise.
  • bit 6: high channel 1 clock (~1.79MHz on NTSC).
    • overrides 15KHz mode.
  • bit 5: high channel 3 clock (~1.79MHz on NTSC).
    • overrides 15KHz mode.
  • bit 4: join channels 1 and 2 for a wide period range.
    • use with conjunction with bit 6.
    • channel 2 becomes inaccessible when this is on.
  • bit 3: join channels 3 and 4 for a wide period range.
    • use with conjunction with bit 5.
    • channel 4 becomes inaccessible when this is on.
  • bit 2: high-pass filter (channels 1 and 3).
    • filtered output on channel 1 (I suggest you to set channel 3 volume to 0).
    • use for PWM effects (not automatic!).
  • bit 1: high-pass filter (channels 2 and 4).
    • filtered output on channel 2 (I suggest you to set channel 4 volume to 0).
    • use for PWM effects (not automatic!).
  • bit 0: 15KHz mode.
• 12xx: toggle two-tone mode.
  • when enabled, channel 2 modulates channel 1. I don't know how, but it does.
  • only on ASAP core.