Some of this is known to be incorrect. I'll correct this in a few months after a bit more RE work. Merry (talk) 21:10, 28 January 2016 (CET)
- Note that everything below will vary depending on the exact DSP firmware used and different variants have slightly different behaviours.*
The DSP communicates with the application through two shared memory areas 0x8000 bytes long each (at 0x1FF50000 and 0x1FF70000 respectively). The DSP alternates between the use of these two areas (much like a double-buffer). Each area has 15 structures within it. The location of these structures can be obtained by reading channel 2 of the DSP pipe. A list of structures in the order the DSP addresses are read from the pipe follows:
1. Frame count
2. Input configurations
3. Input status
4. Input ADPCM coefficients
5. DSP configuration
6. DSP status
7. Output samples
8. Intermediate mix samples
9. Compressor table
10. DSP debug statistics
11. Unknown Coefficients
12. Unknown Coefficients
13. Unknown Coefficients
14. Unknown Coefficients
15. Unknown Coefficients
The DSP has 24 inputs, each of which are individually configurable. These 24 inputs each produce three sets of 4 audio channels (two left, two right).
These four audio channels feed into three intermediate mixers. Two of these intermediate mixers are used for effects and aux.
Frame Count
Input Config
A 192 byte long structure. There are 24 of them.
| Offset | Type | Description |
| 0 | u32 | Dirty flags |
| 4 | 70 bytes | TODO |
| 74 | u16 | Bitmap of which buffers in queue are dirty |
| 76 | Buffer[4] | Buffer queue |
| 156 | u32 | - |
| 160 | u16 | Is Active |
| 162 | u16 | Sync Count |
| 164 | 8 | TODO |
| 172 | u32 | Physical address of current buffer |
| 176 | u32 | Number of samples in current buffer |
| 180 | u16 | bits[0:1]: 1 = mono, 2 = stereo; bits[2:3]: buffer format, bits[5]: fade in |
| 182 | u16 | ADPCM predictor/scale |
| 184 | s16 | ADPCM y[n-1] |
| 186 | s16 | ADPCM y[n-2] |
| 188 | u16 | bit[0]: ADPCM updated?; bit[1]: Is looping? |
| 190 | u16 | Buffer Id of this current buffer |
Buffer
| Offset | Type | Description |
| 0 | u32 | Physical Address |
| 4 | u32 | Sample Count |
| 8 | u16 | 4 bits: ADPCM Predictor, 4 bits: ADPCM Scale |
| 10 | s16 | ADPCM y[n-1] |
| 11 | s16 | ADPCM y[n-2] |
| 14 | u8 | ADPCM dirty? |
| 15 | u8 | Looping? |
| 16 | u16 | Buffer Id |
| 18 | u16 | - |
Simple Filter
This is a standard single-pole filter. The fall-off is 6dB per octave as you would expect.
| Offset | Type | Description |
| 0 | s16 | b0 |
| 0 | s16 | a1 |
Input status
Read only.
Input ADPCM coefficients
DSP configuration
Delay Effect
Delay with feedback.
Length of delay is a multiple of audio frames. There are 160 samples per audioframe.
Feedback arm only has a gain on it. Under the feedback arm is a single-pole filter with the delay.
Reverb Effect
DSP status
Read only.
Output samples
Read only.
PCM16.
Intermediate mix samples
Read/Write.
PCM32. Also serves an aux function, allowing the ARM11 to apply custom effects to audio.
Compressor table
A precomputed response curve lookup table for the compressor.