scspadpcm: A C repository from celeriyacon

This is a proof of concept Sega Saturn 8-channel ADPCM decoder, with the
decoding being done on the SCSP, utilizing all 32 SCSP slots and the majority
of the SCSP DSP's resources.  It runs at a fixed rate of 44.1KHz, and supports
(custom) 1.5-bit, 2.5-bit and 4.5-bit(average) encodings, similar in concept
to other ADPCM formats like BRR and CD-XA ADPCM.

Two DSP-generated PSG-like channels are also provided, one 50/50 square and 
a 4-operator saw wave channel.  The square wave channel isn't suited to music,
as it only supports frequencies of 44100 / (2 * n), where 'n' is an integer,
but should be adequate for sound effects.  The saw wave channel can be
programmed to generate noise, and its output has a programmable simple IIR
filter, which can be used to color white noise.  The relative phases of the
saw wave channel's operators cannot be guaranteed nor reset currently.

Each ADPCM block encodes 16 samples, and playback startup on a channel
currently has a delay of 16 samples(1 block) plus sound driver overhead.

To enable looping, set the comment tag/field in the WAV file to "adp_loop=n",
where 'n' is the loop target, aligned to a 16 sample boundary.

Streaming playback is not currently supported by the included demo sound
driver and tools, but could be supported in theory.

The tools require "libsndfile" to compile and run, and building the ISO
image requires the "genisoimage" utility.  The 68K sound driver and
SH-2 test program were developed with and tested with gcc 4.7.4.  Later
versions of gcc may work, but were not tested.

The contents of "saturnboot.bin" between offsets 0x100 and 0xEFF, inclusive,
should not be used outside of the limited purpose of allowing disc
recognition and booting by the Sega Saturn's BIOS.
celeriyacon/scspadpcm
