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. This flag is only set to value 1 for the first command(once processing for the entire command chain is finished) at the offset specified in the service command, not all type0 commands in the chain.
|
| 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 0x0
| Index Byte
|
Size
|
Description
|
| 0x2
|
2
|
CmdID 0x0
|
| 0xC
|
4
|
Flag, normally value 1.
|
| 0x10
|
0x10
|
Unused, all-zero.
|
User processes use this command prior to cmd3 for initializing looping.
Command 0x1
| Index Byte
|
Size
|
Description
|
| 0x2
|
2
|
CmdID 0x1
|
| 0xC
|
4
|
Value
|
| 0x10
|
0x10
|
Unused, all-zero.
|
This command starts playing the audio channel with value=1. Once the audio channel is playing, value=0 pauses the audio channel playback, and value=1 resumes the audio channel playback. Value=1 has no affect when the audio channel is already playing, likewise for value=0 when the audio channel is not playing.
Command 0x2
| Index Byte
|
Size
|
Description
|
| 0x2
|
2
|
CmdID 0x2
|
| 0xC
|
1
|
Encoding, this is the same as the values used with command 0xE.
|
| 0x10
|
0x10
|
Unused, all-zero.
|
This sets the encoding field in the CSND channel CNT register(that field is cleared to zero first), command 0xE also sets this field.
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. CSND module writes these fields to the channel register for the second physical-address, and the channel register for the byte-size.
Command 0x4
| Index Byte
|
Size
|
Description
|
| 0x2
|
2
|
CmdID 0x4
|
| 0xC
|
1
|
Looping value, this is the same as the values used with command 0xE.
|
| 0x10
|
0x10
|
Unused, all-zero.
|
This is the same as cmd2 except for the looping field. CSND will only write to this channel CNT register for updating the looping field if bit15 in the channel CNT register is value zero.
Command 0x5
| Index Byte
|
Size
|
Description
|
| 0x2
|
2
|
CmdID 0x4
|
| 0xC
|
4
|
Value
|
| 0x10
|
0x10
|
Unused, all-zero.
|
When value=0, CSND module will clear bit7 in the channel CNT register. Otherwise, CSND module sets bit7 in the channel CNT register.
Command 0x6
| Index Byte
|
Size
|
Description
|
| 0x2
|
2
|
CmdID 0x4
|
| 0xC
|
4
|
Value
|
| 0x10
|
0x10
|
Unused, all-zero.
|
This is the same as cmd5, except this updates channel CNT bit6 instead. CSND module will only update CNT here if bit15=0 in CNT.
Command 0x7
| Index Byte
|
Size
|
Description
|
| 0x2
|
2
|
CmdID 0x4
|
| 0xC
|
1
|
Value
|
| 0x10
|
0x10
|
Unused, all-zero.
|
This is similar to cmd2, except this updates channel CNT bit1-bit0.
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 value is written to the channel CNT high-u16, which command 0xE also writes to. 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 0xA
| Index Byte
|
Size
|
Description
|
| 0x2
|
2
|
CmdID 0xA
|
| 0xC
|
4
|
Main physical address
|
| 0x10
|
0x4
|
Audio data byte-size
|
| 0x14
|
0xC
|
Unused, all-zero.
|
Like command 0xE, this writes the specified parameters to the CSND channel slot registers for the main audio-data physical address, and the register for the data byte-size.
Command 0xB
This command is used for initializing IMA-ADPCM state(when IMA-ADPCM encoding is used), prior to using command 0xE. CSND channelslotregister+0x18 = (u16)cmdword[3] | ((cmdword[4] & 0xFF)<<16). CSND channelslotregister+0x1C = 0.
Command 0xC
This is used for initializing looping state for IMA-ADPCM encoding. channelslotregister+0x18 = (1<<31) | (u16)cmdword[3] | ((cmdword[4] & 0xFF)<<16).
Command 0xD
| Index Byte
|
Size
|
Description
|
| 0x2
|
2
|
CmdID 0xD
|
This command is invalid, using this command would result in CSND module immediately continuing to process the command(s) following this one(if any).
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(only needs set if a flag is set which enables using this address).
|
| 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. When looping is used, audio playback initially begins with playing from the first physical address(using the byte-size from the channel register when audio playback was triggered). Once looping begins after the initial audio playback finishes, the second physical address is used for the beginning of the audio data instead(using the same byte-size used with the initial audio playback).
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.