[LAU] Many identical cards - how to keep them straight

[Arnold Krille]

Am Sonntag, 9. März 2008 schrieb Mark Knecht:
> On Sun, Mar 9, 2008 at 3:52 PM, drew Roberts <zotz at 100jamz.com> wrote:
> > On Sunday 09 March 2008 18:44:21 Mark Knecht wrote:
> >  > Hi,
> >  >    I'm aware of and use standard Alsa methods to keep different sound
> >  > cards in the same system straight as far as Alsa is concerned. I'm
> >  > wondering what the proper process would be to keep 3 HDSP9652's which
> >  > are physically in the same system, or multiple USB sound devices
> >  > external to the system, straight as far as Alsa is concerned. I'd like
> >  > to know that a certain card always will be always be card 0, card 1 or
> >  > card 2. I do not want Alsa or Linux to make this decision for me and I
> >  > certainly don't want Alsa to change them from boot cycle to boot
> >  > cycle.
> >  I needed to solve this problem a while back. The best help I got was
> > telling me it was not possible.
> Humm, that's a pretty glaring disappointment, assuming it's true, and
> I have no reason to believe it isn't.

Probably the one giving that answer was me. It is not entirely impossible. The 
solution is roughly:
1) You need to keep the clocks of the cards in sync.
   - Either you got professional cards which allow to sync to adat/world 
clock/spdif. Then its easy, just make them all sync to the same source.
   - If you don't have that high cards:
     Break out your soldering iron, unsolder the time-giving quartz on all the 
soundcards except one and feed the quartz-signal from that "master" to all 
the "slaves".
Now the cards don't fire interrupts at different times, because of different 
sample-rates. (48kHz on one card is _always_ different then 48kHz on another 
card if the clocks aren't synced.)
But they still fire individual interrupts...
2) Break out you kernel-hacking skills and mask all the interrupt from the 
soundcards except for one.
3) Fiddle around with an .asoundrc to create one big sound-device out of all 
these to-sync-devices.

There are people who did this. (Search the web and the archives for 
el-cheapo.)
But its not easy. And if you aren't fixed on "as cheap as possible" it is 
easier and more reliable and more stable and of higher soundquality to just 
buy a sounddevice that works and has the needed number of channels.

That is why my answer is: It is not possible. Because it involves fiddling 
with a lot of very advanced stuff and voids warranty on the devices if you 
unsolder the quartz...

Have fun,

Arnold
-- 
visit http://www.arnoldarts.de/
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