Re: [hatari-devel] 2 crossbar questions:

[David Savinkoff <dsavnkff@xxxxxxxxx>]

On Sunday 29 January 2012 08:25, Laurent Sallafranque wrote:
> Hi,
>
> I've playing around with the Warum demo and Moongame game.
>
> Both are using stereo 8 bits in the crossbar, but are using 16 bits
> transfers into the SSI (CRA bits 12, 13 = 10 (16 bits transfers))
>
> This brings me 2 questions about the crossabr and the sound matrix of
> the Falcon :
>
> - When the crossbar is in 8 bits, does the DAC swift the data to 16 bits
> (data can come from the DMA or the DSP)  ?

It looks like the DMA chip switches the data from 8 to 16 bits.

> - in non handshake mode,  the crossbar asks the DSP to send it the
> datas. I guess it gets 8 bits (left or right sample), then the 8 other
> bits, while in the same time the DSP transfers 16 bits before
> considering that it has transferred the whole data. Does it sound right ?

Here is what I can see; by looking at the schematics:
- The DSP56K is connected to the DMA chip.
- The Codec chip is connected to the DMA chip.
- The Codec chip is Not directly connected to the DSP56K
- The Codec chip is 16 bits stereo serial data only.
- The DSP56k can serialize data in many ways from 8 to 24 bits,
   and beyond 2 channel stereo.

Here is my guess:
- The crossbar is either in the DMA chip or connected to it.
- The crossbar communicates 16 bit stereo serial data to the Codec.
- The crossbar converts Non 16 bit stereo serial data to
   16 bit stereo serial data before sending the data to the codec.
- The crossbar probably zero-pads 8 bit data to 16 bits if required,
  and may duplicate mono data for the stereo codec.

> I've recoded the transfer as wriiten above.
> The sound is different for Warum (not better, but different)
> Actually, this breaks Chaos AD which freezes (I don't know why yet, I
> search).
>
> Should I upload this, as I think it's the good way to proceede or not ?
>
> Regards
>
> Laurent