DSP Memory Region

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)

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• 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.

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.

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.

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.