Re: [Discuss-gnuradio] Packet Flowgraph and underflows

[Wolfgang Nagele]

Hi Julian,

Thanks for the pointer. I'm using a HackRF - doesn't look like the
Osmocom sink supports the same construct. Any way of doing something
like this in a more generic approach?

Cheers,
Wolfgang

On Thu, Aug 6, 2015 at 8:50 PM, Julian Arnold <address@hidden> wrote:
> Hi Wolfgang,
>
> no, you do not need to use something like a mute block.
> The functionality you are looking for is already build into UHD (I'm
> assuming you are using a USRP as your transmitting device)
>
> The UHD sink in GNU Radio is able to react to some specific stream tags [1]
> one of which is the length tag.
> You can assign a name for this tag in the UHD source block ('Length tag
> name' field).
>
> Now, if you have assigned a value to this 'Length tag name' field the UHD
> sink is somehow reacting as a tagged stream block [2].
> If samples arrive at the UHD sink, the USRP will only transmit that amount
> of samples specified in the length tag starting from that length tag.
> Therefore, you should not see any 'U' messages no more as the USRP
> automatically stops transmitting and does not expect any more samples
> follow.
>
> However, keep in mind that with tagged streams every first sample of a
> 'packet' needs to have the length tag attached.
>
> E.g consider the following stream of samples where the first sample has a
> length tag assigned to it with value 10:
>
> 1 2 3 4 5 5 7 8 9 10 11
> |                             |
> length tag                next length tag needs to be exactly here
> value = 10 samples
>
> Hope that helps.
> Cheers,
> Julian
>
> [1] https://gnuradio.org/doc/doxygen/page_stream_tags.html
> [2] https://gnuradio.org/doc/doxygen/page_tagged_stream_blocks.html
>
>
> On Thu, Aug 6, 2015 at 12:05 PM, Wolfgang Nagele <address@hidden> wrote:
>>
>> Hi,
>>
>> I've been looking for a solution to this and can't seem to find any
>> examples.
>>
>> If I have a flowgraph that transmits packets for instance from a TCP
>> stream - if this TCP stream only receives data occasionally it will
>> create underflows (showing up as U characters on STDOUT).
>>
>> What is the proper way of handling such a scenario? I thought of using
>> something like the Mute block to transmit a 0 data stream during
>> periods of no data. However that seems excessively complicated to
>> implement and I think I am missing some pointer here ...
>>
>> Thanks,
>> Wolfgang
>>
>> _______________________________________________
>> Discuss-gnuradio mailing list
>> address@hidden
>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>
>
>
>
> --
> Julian Arnold