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

[From: Simon Pickering]

> 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.

The SIO_ functions are documented in the SPRU404l.pdf file available from
the Ti website (just Google for it).

It would be nice if Nokia could release some example code for the use of
these documented functions and the other useful undocumented functions that
are built into the avs_kernel. Specifically those instructions that are used
to produce sound and video output (and things like volume control which is
what the EAP_CC_* commands appear to do).

Regards,


Simon