[maemo-developers] tremor for DSP Re: [maemo-developers] API of the DSP's avs_kernel

[From: SebastienB]

> Then definitely google for "sandvall thesis pdf". If you cannot find the
> source patch with DSP code on the net, let me know. Got it from one of
> rockbox developers.

Thanks, this looks good.

However, the problem for now is how to call into the avs_kernel to send our 
decoded audio to the hardware. Since there is no one at Nokia out there who 
would be willing to give me the specifications, I kept on analysing their 
system.

I took the pcm2.o codec (because it's the simplest one), linked it against a 
dummy kernel (with all empty functions) and disassembled the result. Scarcely 
commented output is at http://lekernel.lya.eu/nokia_dsp/.

I think it works like this :
* On codec initialization, we must first request a stream with the function 
EAP_CC_RequestStream(), then create a SIO (for whatever that means... serial 
input/output ?) with SIO_create().
* For power management, we must tell when we need audio output, using the 
functions SIO_idle() and SIO_reclaim() (but I'm very unsure of this point).
* The decoded audio is sent via SIO_issue().
* There are some extras such as EAP_CC_UnMute(), EAP_CC_Mute(), 
EAP_CC_SetVolume() and EAP_CC_SetPanning() which are probably not important 
for now.

I don't know the function parameters yet.

Sebastien