[hpsdr] Ozy/Mercury Protocol

[Andrea Montefusco]

Alberto I2PHD wrote:
> ***** High Performance Software Defined Radio Discussion List *****

[...]
Many thanks for detailed explanation of WinRad code, Alberto.

 > Of course, all the above is true if the demodulated data are sent again
 > to the FPGA, which uses the same
 > exact clock for input and for output.
> If instead the output goes to a sound card, which has its own sampling 
> clock, things become a little more
> complicated. A difference in the clocks is _unavoidable_ and must be 
> taken into account. Some do drop
> samples or insert empty samples, but this causes clicks or bops.
> This is how I solved the problem in Winrad.

I was seeking this info, because I believe the John (and my) problem in Linux
arises at this point.
The problem now becomes: how do it resample the output stream (to
take in account the audio card clock skew) ?

Indeed, searching better in jack wiki, our case is very similar to
using 2 or more soundcards not synced via wordclock (common clock).
See:
http://trac.jackaudio.org/wiki/WalkThrough/User/AlsaInOut

A crude solution could be to configure jack to ignore audio card (via the dummy driver),
connect DttSP and John's ghpsdr module to the jack patchbay.
Next start

alsa_out -d hw:1 -f 30000

and patch it to the DttSP output via jack patchbay.

Or we can grab the sophisticated Alberto's code, creating a utility program to be used
instead of alsa_out.

      73 *am*

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Andrea Montefusco iw0hdv        http://www.montefusco.com
tel: +393356992791                     fax: +390623318709
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