SND

The SND file, also known as DTPK, is used for both sequenced music and packages of sound effects.
The format is played back via the AM2 AICA driver, located as AICADRV.BIN in the MISC folder on the Dreamcast versions of the game.

SND File format

Header

Position	Length	Type	Description
0x00	0x04	string	Identifier 0x4454504B (DTPK)
0x08	0x04	uint	Size of file
0x3C	0x04	uint	Location of Sample Table

Sample Table

Position	Length	Type	Description
0x00	0x04	uint	Index of last sample (Add 1 for number of samples)
0x04	N/A	N/A	First sample entry (0x10 bytes each)

Sample Entries

Position	Length	Type	Description
0x00	0x04	uint	Sample Location & Type packed as follows:
	& 0x007FFFFF		Sample Offset
	& 0x00800000		Sample quality. 0 Normal, 1 Half
	& 0x01000000		Format flag - 0 PCM, 1 ADPCM
	& 0x02000000		Unknown flag. Is NOT Mono/Stereo
0x04	0x2	ushort	Loop start offset from start of sample
0x06	0x2	ushort	Loop end offset from start of sample
0x08	0x4	uint	Related to sample frequency. Either 0 or 0x80. 0x80 = Half sample rate
0x0C	0xC	uint	Size of sample data

AICA Driver

The AICA driver is loaded right into the start of AICA RAM at 0. The driver always loads the SND file for music into the hard-coded offset of 0x10000. Subsequent files can be loaded after that, the offset(s) written to a table found at 0xDB00 with 0x20 byte entries per file. The table contains 8 slots, (ends at 0xDC00) and they don't always need to be filled in order. This loaded files table will be further documented later.

AICA Driver Commands

There is a rolling buffer from 0x400 to 0x500 in memory where 4 byte commands are sent to the driver. As each command is executed, the sound driver clears those bytes back to 00. New commands should be sent to the next set of 4 bytes and roll back to 0x400 once you hit 0x500. Commands to be documented when further understood.