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Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and
From: |
Nowlan, Sean |
Subject: |
Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB |
Date: |
Tue, 21 Oct 2014 17:19:20 +0000 |
>From Marcus:
> ... and that (wut) might be a bug, because it implies that, if the stream has
> both a time tag and a sob tag, the
> question whether the tx metadata has a time tag depends on in which order
> these tags are sorted on the the
> tag storage multimap. Which might be random, because tags are sorted only by
> tag offset.
> @Martin: is there a reason that this is explicitely set to false here, or can
> one just fix this by deleting a line?
This appears to be handled correctly. Given the same tag offset, the order of
tx_time vs. tx_sob tags should not matter. If tx_time is found first, it sets
found_time_tag=true and _metadata.has_time_spec=true (lines 652 & 653). Then
_metadata.has_time_spec is overwritten in the tx_sob check (line 665) with
'false', but is set back to 'true' in line 743 due to found_time_tag being
true.
if (found_time_tag) {
_metadata.has_time_spec = true;
}
If instead tx_sob is found first and tx_time second, then the time spec will
also be set in line 743. So the question is whether setting
_metadata.has_time_spec=false is really necessary. I'd say it's worth keeping
in case the user doesn't always want to use tx_time stamps. The user may want
to schedule some bursts but force others to transmit as soon as possible while
still using the ATR functionality of the USRP.
I know all this logic can be hard to follow, but it has to handle so many
different cases and possibly span many calls to work and tag_work.
>From Frederik:
> Unfortunately, even with the newest version the USRP is still transmitting
> its carrier over the air. I tried both with
> the Message Burst Source as well as with the Stream to Tagged Stream Block
> combined with setting a Length Tag
> name in the USRP Sink. With the Tag Debug Block I see tx_sob+tx_eob and the
> Length Tag, respectively. They all
> seem to be at the right place and have the right value.
>
> The Length Tag should arrive properly at the Sink. I checked by changing the
> tag's name at the Stream to Tagged
> Stream Block to something stupid and finally got an "tG" printed out.
It should be mentioned that there are two burst tag interfaces that cannot be
mixed. if a Length Tag Name is specified to the constructor, all tx_sob and
tx_eob tags will be ignored in tag_work to ensure the interfaces are mutually
exclusive. If no Length Tag Name is specified, then tag_work will search for
tx_sob/tx_eob tags and won't look for length tags.
Sean
On 21.10.2014 15:53, Frederik Wing wrote:
> Hi Marcus,
>>>> I cannot believe that there is no solution to it since the
>>>> "tags_demo" application shows that it is indeed possible.
>>>> :-/
>> that makes the two of us! I didn't get that when using tags_demo,
>> you're not seeing the carrier that you use tags_demo; as far as I
>> understood, your application does exactly the same, sending bursts
>> with sob/eob tags?
>
> That's right. tags_demo works perfectly. No carrier in between the
> bursts. The flow graph I posted before sends exactly one burst with
> SOB and EOB tags. The only difference to tags_demo I could recognize
> so far is that I don't assign time stamps to the samples.
> But this shouldn't be a problem, should it?
>
> Frederik
>
>
> _______________________________________________ Discuss-gnuradio
> mailing list address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>
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- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, (continued)
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Martin Braun, 2014/10/20
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Frederik Wing, 2014/10/20
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Marcus Müller, 2014/10/20
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Frederik Wing, 2014/10/21
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Marcus Müller, 2014/10/21
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Frederik Wing, 2014/10/21
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Marcus Müller, 2014/10/21
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Frederik Wing, 2014/10/21
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Martin Braun, 2014/10/21
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Marcus Müller, 2014/10/21
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB,
Nowlan, Sean <=
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Marcus Müller, 2014/10/21
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Nowlan, Sean, 2014/10/21
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Marcus Müller, 2014/10/21
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Nowlan, Sean, 2014/10/21
- Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Frederik Wing, 2014/10/22
Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB, Frederik Wing, 2014/10/22