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
|
Type0 CommandsCommand 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
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.