[hpsdr] about latency growth with HPSDR

[Riho B., ES7AAZ]

Steve,

It may be right that SDR is not capable to run time sensitive applications.
I was scoping 10Mhz WWV today, output shows that real time/SDR time
varies, escpecially while minimizing and maximizing PowerSDR window
which causes higher CPU load. IIt was @ 48kHz sampling rate  all over
the path, biggest buffers, no audioble drop-outs, max DPC latency 170?s.
Anyway, it's now clear why's there are drop-outs while listening DRM, why's
there are out of sync line blocks in SSTV, why's digital SSTV misses the 
blocks.
I'm not struggling with it anymore. All the other, CW and SSB works just 
fine.





73's,
Riho, ES7AAZ.


29.09.2011 23:56, Steve Bunch kirjutas:
> Riho,
>
> I can't answer your question exactly, but this can happen because of 
> buffering somewhere in your sample chain, when the sampling rate of 
> your system is slightly slower than realtime so the samples aren't 
> being consumed as fast as they're generated.  The unread samples are 
> saved up somewhere, and accumulate there.  I had this happening to me 
> in an ALSA-based Linux system -- I would over time be listening 
> several seconds behind realtime when using a USRP to listen to FM 
> radio.  Restarting the chain will clear out the buffered data; when 
> you restart it will grow again.
>
> I don't know if the Ozy/Mercury sample chain is capable of buffering 
> this much data (someone familiar with it should be able to tell you 
> exactly how much can be buffered there), but in my case it was in my 
> audio system.  Unfortunately, I don't know the various Windows audio 
> systems well enough to give you any help, but that is where I would 
> look first.
>
> Steve, K9SRB
>
> On Sep 29, 2011, at 3:07 AM, Riho B., ES7AAZ wrote:
>
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> Hi,
>>
>> I have a program called Faros which is a beacon monitor.
>> Faros gets his time sync from ntp GPS time servers.
>> NCDXF network beacons have GPS dicsiplined controller
>> which allows path delay calculation and Faros does it.
>>
>> After 2h running I see 120ms latency growth (linear graph)
>> and it's growing on. Which means that radio waves are traveling
>> about one  more circle around the world. It can't be so. Restarting
>> PowerSDR brings the latency back to its initial state. Exactly the same
>> effect with CWSkimmer console. It's almost same vith VAC and with
>> analog audio cable.
>>
>> The question is not even about latency itself or how much it is.
>> The question is why's latency growing and how much it does?
>>  Is it somewhere in USB connection ?  I'm Ozy user.
>>
>>
>>
>> 73,
>> Riho, ES7AAZ
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