synchronizing sound cards in a cluster

[alvin]

Jim Lux wrote:

> Anybody have any good ideas on how to synchronize the sampling from 
> multiple sound cards in a cluster using Ethernet as the interconnect. 
> The application would grab data from the sound card (notionally at 100 
> ksamples/second total, for two channels) and do a ton of signal 
> processing.  At some point in the processing, the streams of data need 
> to be shared between processors (i.e. to do beamforming), and so, 
> needs to be time registered.
> The bandwidth isn't a real challenge here (with, say, 16 processors, 
> that's only about 32 Mbps total), nor is latency, but synchronization is.
>
> One can fairly easily synchronize to a millisecond over Ethernet, but 
> this application needs sync to, at worst, 1 sample time (20 
> microseconds) although order of a microsecond would be nice.
>
>
>
> James Lux, P.E.
> Spacecraft Telecommunications Section
> Jet Propulsion Laboratory, Mail Stop 161-213
> 4800 Oak Grove Drive
> Pasadena CA 91109
> tel: (818)354-2075
> fax: (818)393-6875
>
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you could use ntp to synchronize the systems I believe that with a 
little effort you can get ntp to sync the clocks on systems to sub 
milisecond times.

A much better solution would be to inject a signal into all the input 
streams that you can extract and sychronize to.

Another possibility would be to connect all the serial ports on all the 
systems and use one of the modem control lines to inject a square wave 
that you use for synchronization.

-- 
Alvin Starr                   ||   voice: (416)785-4051
Interlink Connectivity        ||   fax:   (416)785-3668
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