. A phoneme will continue playing back infinitely; unless the phoneme is changed or CTL=1.
. Reset doesn't affect SSI263/SC01 (so phonemes continue to play).
. CTL=1 sets "PD" (Power Down / "standby") mode, also set at power-on.
. CTL=0 brings device out of "PD" mode, the mode will be set to DR1,DR0 and the phoneme P5-P0 will play.
. Setting mode to DR1:0 = %00 just disables A/!R (ie. disables interrupts), but otherwise retains the previous DR1:0 mode.
. RESET is not connected to !PD/!RST pin 18.
. Support edge-case where RESET can enable ints & assert IRQ.
. Power-on: PD=1 (so D7=0), reg4 (Filter Freq)=0xFF.
. Support SSI263 IRQ and D7 on a Phasor mode change (including Echo+).
. $Csxx I/O mapping (same for Mockingboard and Phasor mode).
Other:
. SSI263 save-state: support SC01 as a sub-unit of the card.
. 6522: Fix reg $F (ORA w/HS) to be identical to reg $1 (ORA).
Differences compared to Mockingboard:
. TIMER1 underflows to $FFFE before it's reloaded with latch.
. TIMER1's LATCH=$0000 gets interpreted as $FFFF.
. Partial TIMER2 support: IFR.T2 gets set on underflow. But T2 reads as 0x00FF.
. AY register reads are unsupported (always read as 0).
Config->Sound: show 'MEGA Audio' in drop-down menus only if it was specified on the cmd line.
. For MB: isChipSelected[0] = true. So do this on Reset() or for Phasor when switching to MB mode.
. Add "Notes on Phasor's AY-3-8913 chip-select & r/w"
. Refactor some common code into SY6522::UpdatePortAForHiZ()
Mockingboard or Phasor cards can be inserted into any slot.
Change Config->Sound to that slots 4+5 to be individually selected for the 3 soundcard types.
Add MockingboardCardManager class to manage multiple cards and mix the sound buffers.
