Re: Re: au88x0 modem

[Manuel Jander <manuel.jander@gmail.com>]

Hi,

> The easy way is to create a PCM device "modem" on au8810
> 
> 
> DMA -> FIFO -> SRC -> MIXIN --------> MIXOUT -> MC97(Modem Out)
>                          |
> 		        +-----------> MIXOUT -> EQ -> AC97(Audio Left)
> 
>     				Modem Speaker  On or Off
> 
>                                    +-> MIXOUT -> EQ -> AC97(Audio Right)
>                                    |
> DMA <- FIFO <- SRC <- MIXOUT <- MIXIN <-------- MC97(Modem IN)
> 
> 
> or
> 
> 
> DMA -> FIFO -> SRC -> MC97(modem) (Playback)
> 
> DMA <- FIFO <- SRC <- MC97(modem) (Capture)
> 

Remove the samplerate converter, it does not make any sense on a modem.
You will only loose signal precision with the samplerate converter
anyway, and there are very few of them. 
A direct route from the fifo to the modem codec will do it and the modem
signal device will run at the codec native samplerate without any
precision loss.

> 
> What is the difference between modem application and audio application ?

Nothing. The only modem extra functionality is the ability to switch the
modem line off/on hook. It just sends and captures QAM modulated
signals.

> Do the modem application open two PCM streams (one for playback and the 
> other for capture )?

Yes, it should be full duplex. This will require 2 DMA's.

> Where is the class SND_PCM_CLASS_MODEM specificed in the driver ?

At least i did not.

Best Regards,
Manuel Jander




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