audio streaming notes.txt

How it roughly works on the DVD Drive:
Audio Streaming works by telling the DVD Drive to Start Playing a Stream from disc offset X for Y length.
The drive will internally convert the adpcm like data to pcm and then ship it off to the DSP to be resampled/mixed in with any audio that may be playing.

How we can make it work with a DMA based DVD Drive replacement:
1. Install a custom Ext Interrupt handler which will check DVD reads if they are our Audio Streaming reads or normal.
2. On Audio Stream command received (DVDStopStreamAtEndAsync(0xE1000000,u32 addr, u32 len);), queue read for 4096 bytes of adpcm data.
2. On Audio Stream queued read complete (detected from our custom Ext Interrupt handler), decode the adpcm data + downsample from 48043Hz to 32000Hz.
3. On AIStartDMA, store the memory address and length somewhere from the DSP registers.
4. Watch out for the DSP mail message (in DSPReadMailFromDSP: 0xDCD10002) to arrive, mix in our decoded/downsampled stream in with the stream which is about to be played (the addr/len we stored in step 3). Then repeat from step 1 with stream offset+=4096;

Note1: 4096 bytes of adpcm decodes to 3584 samples per channel, so 3584 * 2 channels * 2 bytes per sample = 14336 bytes.
Note2: Implement a response to DVDLowRequestAudioStatus


Steps to implement this:
1. Use a standard DVD drive and an Audio streaming game (Wave Race: Blue Storm).
2. Log the DVD Audio Streaming & Read commands via a normal disc.
3. Disable the DVD Audio Streaming commands and then implement them with the method described above.
4. Try this on a DVD replacement (Wode, Wiikey Fusion).


DVD Functions from http://www.crazynation.org/GC/GC_DD_TECH/GCTech.htm:

-- 
DVDLowRequestAudioStatus E2xx0000

xx=0 is stream playing?
response: 0,0,0,y
y=1 yes;0=no

xx=1 what is the current address
response: y,y,y,y
y=address of current audio buffer that is burning on disk with 0x2000 granularity
remember address is actaul byte offset>>2
i.e. it has a granularity of 0x8000 bytes which is 0x2000

xx=2 what was the start address of currently playing audio stream
response: starting address of current audio stream >>2

xx=3 what was the length of currently playing audio stream
response: length of current audio stream
--

--
DVDCancelStreamAsync E1010000,xxxxxxxx,yyyyyyyy

response: 0,0,0,0
cancel current audio stream
--

--
DVDStopStreamAtEndAsync E1000000,xxxxxxxx,yyyyyyyy
response: 0,0,0,0
start audio stream at x with length y
if x and y are zero then will stop audio stream at end of buffer.
if not zero then will add another stream to queue, when current one finishes
then next one will be played.
Queue is only 1 level deep, and is replaced by last command issued.
--