[alsa-devel] Enabling in-kernel synch for M-Audio boards

[Ludovico Verducci]

Il giorno 18/set/07, alle ore 15:50, Clemens Ladisch ha scritto:

> John Rigg wrote:
>> On Tue, Sep 18, 2007 at 10:07:05AM +0200, Ludovico Verducci wrote:
>>> As far as I know the delta family boards drivers support the
>>> synchronization of up to 4 audio boards over PCI: at the moment I'm
>>> reverse engineering the hardware trying to understand how this  
>>> can be
>>> accomplished.
>>
>> I'm aware that some Windows users are using several Delta 1010s
>> without external sync, but I'm not sure how it is done (or how
>> good it sounds). AFAIK it would require a VCXO so that the frequency
>> of the card's clock could be varied by enough to keep it in sync
>> (ie. making the clock oscillator part of a phase locked loop).  
>> Looking
>> at the PCI card on the 1010, I can only see standard fixed-frequency
>> crystals. The only PLLs appear to be the internal PLL in the S/PDIF
>> receiver and the 4046 PLL chip for the word clock input signal.

Yes, I agree. If there's a way to achieve this kind of  
synchronization it isn't simple, at first sight. I'm trying to  
reconstruct the board's schematics and studying components' data  
sheets to figure out a way to make it work.

> In theory, it should be possible to use the PCI clock (between 25 and
> 33 MHz) as input for one of the PLLs, probably after dividing it down.

This could be also an option, but I really hope that the feature can  
be implemented in software because I surely cannot synch over  
ethernet the PCI clocks!
Let's see...

Regards,
Ludovico