==== Enhanced Apple Sound Chip (EASC) ====

== Memory Map ==
All offsets from the base address of the chip

^Starting offset^Function^
|0x000|FIFO A|
|0x400|FIFO B|
|0x800|Version (read-only) EASC returns 0xB0.|
|0x801|Mode: 0 = disable (repeat last sample output infinitely), 1 = run |
|0x802|Overflow flag: bit 7 set if engine overrun|
|0x803|FIFO clear strobe (bit 7)|
|0x804|FIFO interrupt status: bit 0 = A half full, bit 1 = A full/empty, bit 2 = B half full, bit 3 = B full/empty|
|0x806|Volume control (top 3 bits only)|
|0x807|Clock rate select on ASC: hardwired to return 0x03 here|
|0x80A|Channel A play/record: bit 0 = 0 for play, 1 for record, bit 1 = 0 for 11 kHz record, 1 for 22 kHz record|
|0x80F|Test logic control (bit 7)|
|0xF00|A write pointer high|
|0xF01|A write pointer low|
|0xF02|A read pointer high|
|0xF03|A read pointer low|
|0xF04|A sample rate time increment high|
|0xF05|A sample rate time increment low|
|0xF06|A left volume|
|0xF07|A right volume|
|0xF08|A FIFO control (bit 7 = 1 to enable CD-XA decompression)|
|0xF09|A interrupt control (bit 0 = 1 to enable buffer half-full IRQ)|
|0xF10-0xF17|A CD-XA decompression filter constants|
|0xF20|B write pointer high|
|0xF21|B write pointer low|
|0xF22|B read pointer high|
|0xF23|B read pointer low|
|0xF24|B sample rate time increment high|
|0xF25|B sample rate time increment low|
|0xF26|B left volume|
|0xF27|B right volume|
|0xF28|B FIFO control (bit 7 = 1 to enable CD-XA decompression)|
|0xF29|B interrupt control (bit 0 = 1 to enable buffer half-full IRQ)|
|0xF30-0xF37|B CD-XA decompression filter constants|

Notes: 
- The filter constants for CD-XA mode are programmable.  By default they are the values from the Yellow Book spec: 0x00, 0x00, 0x00, 0x3C, 0xCC, 0x73, 0xC9, 0x62.
- The two FIFO spaces do not differentiate between addresses inside of them: a read or write anywhere in 000-0x3FF will read/write the next byte for FIFO A.  On the original ASC this was true of normal sample playback mode but not wavetable mode.  EASC does not support wavetable mode.