Re: [Discuss-gnuradio] Scheduler enhancement?

[Marcus Müller]

Hi Piotr,

As far as I grok the gr-osmosdr rtl_souce, this is an overflow
indication purely based on the fact that in the rtl_source itself, the
number of the last used buffer is compared with the maximum number of
buffers that should be – and if that happens, that is an indication that
the software side noticed things ran over how much buffer there's
available.

That's pretty different from the USRP approach: It is indeed a kind of
overflow indication, but it gives no chance whatsoever to recover, since
the rtl dongle isn't aware of it, and also has no means to actually time
stamp data. If things get really bad, and USB buffers get lost before
they even reach userland, librtl can't even notice, I think (the USB
bulk transfer packets are pretty much samples only, as far as I read
librtlsdr's librtlsdr.c in combination with rtl_source_c.cc), so there's
no timing/"original sample count" info available. USRPs actually keep
track of ACKs coming from the PC.

Best regards,
Marcus

On 22.07.2016 10:45, Piotr Krysik wrote:
> W dniu 22.07.2016 o 09:34, Sylvain Munaut pisze:
>> Hi,
>>
>>> It's a little bit off-topic but if someone will change the gr-osmosdr,
>>> it would be great to have other stream tags that we are used to see at
>>> the output UHD source. For example if the source prints on the output
>>> that there is some problem with transmission it would be great to add a
>>> stream tag at that moment. In Multi-RTL
>>> (https://github.com/ptrkrysik/multi-rtl/) currently any such event means
>>> that synchronization of channels is lost until user manually calls
>>> resynchronization. Because there is no way to detect samples loss
>>> resynchronization can't be called automatically.
>> rtl-sdr can't detect sample loss ...
>>
>> With USRP, the hw reports overflows to the host, but the rtl-sdr has
>> no such thing, it will drop sample silently if its internal buffers
>> overflow.
>>
> Here is some form of detection of overflows:
>
> http://git.osmocom.org/gr-osmosdr/tree/lib/rtl/rtl_source_c.cc#n305
>
>
> What you are saying means it doesn't detect 100% of overflows?
>
>
> Best Regards,
>
> Piotr Krysik
>
>
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