CSND Shared Memory

This page describes the structure of the CSND shared memory.

Type0 Command Structure

Index Byte	Size	Description
0x0	2	Offset in shared-memory for the command to process immediately after this one, when not 0xFFFF.
0x2	2	CommandID
0x4	1	This is initially zero when this command data is written by the user process, once the CSND module finishes processing the command this is set to 0x1.
0x5	3	Padding?
0x8	4	The low 5-bits for this field is the the channel-index. This word is used for command parameters as well.
0xC	0x14	Command parameters

Command 0x1

Index Byte	Size	Description
0x2	2	CmdID 0x1
0xC	4	Value
0x10	0x10	Unused, all-zero.

This command triggers playing the audio channel from the beginning of the audio data, when the audio channel was already playing this results in the audio channel restarting from the beginning. The result is the same with values 0 and 1, even when the audio channel was already playing.

Command 0x3

Index Byte	Size	Description
0x2	2	CmdID 0x3
0xC	4	Physical address of the first audio sample in the loop.
0x10	4	Total byte-size of the loop sample-data.

This initializes state for looping, when looping is used. This command is used immediately after command 0x8.

Command 0x8

Index Byte	Size	Description
0x2	2	CmdID 0x8
0xC	4	s32 value = (s32)(6.7027964E+07f / ((float)samplerate * 1.0f))

This sets the sample rate. This command is used immediately after command 0xE.

Command 0x9

Index Byte	Size	Description
0x2	2	CmdID 0x9
0xC	4	Unknown
0x10	0x10	Usually zero?

This command must be used after command 0x8(user processes use cmd8 a second time before using this command). The parameter values seem to have no affect when not using IMA-ADPCM encoding?

Command 0xB

Index Byte	Size	Description
0x2	2	CmdID 0xB
0xC	2	User processes set this to: cwav_imaadpcminfo.data
0x10	1	User processes set this to: cwav_imaadpcminfo.tableindex
0x11	0xF	Unused, all-zero.

This command is used for initializing IMA-ADPCM state(when IMA-ADPCM encoding is used), prior to using command 0xE.

Command 0xE

Index Byte	Size	Description
0x2	2	CmdID 0xE
0x8	4	See below.
0xC	4	See below. Usually zero?
0x10	4	See below. Usually zero?
0x14	4	Physical address for the audio data, for the main channel.
0x18	4	Physical address for the audio data, for the second channel when not 0x0(stereo audio).
0x1C	4	Total byte-size for the audio data.

This initializes the CSND channel registers located at: 0x1EC03400 + (channel_index*0x20). Whether mono/stereo audio is used is determined via an unknown flag.

Parameter word 0x8

Bit	Description
5-0	Channel index
9-6	?
11-10	1 = enable looping, 2 = disable looping.
13-12	This sets the encoding, the names for the following encodings are from here. 0 = PCM8 and DSPADPCM, 1 = PCM16, 2 = IMAADPCM.
15-14	?
31-16	Sample rate clamped to the following range(by the user process): 0x42-0xFFFF. This is the same value used with Cmd 0x8, except clamped.

Parameter word 0xC

Bit	Description
15-0	Unknown, this value is clamped to the following range(by the user process): 0x0-0x8000.
31-16	Unknown, this value is clamped to the following range(by the user process): 0x0-0x8000.

Parameter word 0x10

Bit	Description
15-0	Unknown, this value is clamped to the following range(by the user process): 0x0-0x8000.
31-16	Unknown, this value is clamped to the following range(by the user process): 0x0-0x8000.

Command 0x300

Index Byte	Size	Description
0x2	2	CmdID 0x300
0x8	0x18	Unused, all-zero.

CSND module writes state info(including state from CSND registers) for each audio channel to shared-memory for this command.