Re: [Discuss-gnuradio] how does Packet Header Generator module handle tags

[Martin Braun]

Before myths about tagged stream blocks start perpetuating the webs:
TPP_DONT on a tagged stream blocks does the same as on any other type of
block; however, TSB tags still get through.

A closer inspection of packet_headergenerator_bb (either by reading the
source code or the manual page
(http://gnuradio.org/doc/doxygen/classgr_1_1digital_1_1packet__headergenerator__bb.html#details)
reveals that the actual processing is done in a separate kernel, the
header formatter object, which is user-defined. See
packet_header_default for an example.

M

On 07/20/2014 04:54 PM, Marcus Müller wrote:
> Hi Tiankun,
> 
> On 20.07.2014 15:50, hutiantian wrote:
>> Hi Marcus,
>> My tx_ofdm.py is gen by tx_ofdm.grc, there are a
>> 'packet_headergenerator_bb' module in it. This module use
>> 'set_tag_propagation_policy(TPP_DONT)' to handle tags by itself.
> Ah ok!
>> I didn't find any code has touch tags in this module, but when I
>> connect it to Tag Debug module, I can find the tags output.
> This is indeed strange. However, packet_headergenerator_bb is a subclass
> of tagged_stream_block [1].
> 
>> In my opinion, if one module use
>> 'set_tag_propagation_policy(TPP_DONT)', and it does not handle it,
>> tags will not pass down.
> That's generally correct, but there's the tagged stream block exception:
> [1], "A note on tag propagation" tells us that one most of the time
> would use TPP_DONT to handle all non-length tags, whilst length tags are
> always passed forward.
> 
> Hope that helped!
> 
> Greetings,
> Marcus
> 
> 
> [1] http://gnuradio.org/doc/doxygen/page_tagged_stream_blocks.html
>>
>> Thanks
>> Tiankun
>>
>> 于 2014年07月20日 21:15, Marcus Müller 写道:
>>> Hi Tiankun,
>>>
>>> what's your GNU Radio version [1]? Where did you find that tx_ofdm.py?
>>> There is no tx_ofdm.py in my GNU Radio source tree (in none of v3.7.4,
>>> v3.6.5 or v3.4.2). There is a tx_ofdm.grc, which can be used to generate
>>> a tx_ofdm.py, but that does not (and shouldn't) contain a
>>> "set_tag_propagation_policy" line.
>>>
>>> Greetings,
>>> Marcus
>>>
>>> [1] you can find out by running "gnuradio-config-info -v"
>>> On 20.07.2014 14:54, Tiankun Hu wrote:
>>>> Hi Experts,
>>>> I was reading tx_ofdm.py. I found this module use
>>>> 'set_tag_propagation_policy(TPP_DONT)' to handle tags by itself, but I
>>>> cann't find the code that used to handle tag in this module.
>>>> I knew this module will call 'packet_header_ofdm.header_formatter()'
>>>> and
>>>> 'packet_header_default.header_formatter()', but I also cann't find the
>>>> handle tag code in these functions.
>>>> Anyone can help me figure out where does this module process tags?
>>>>
>>>> Thanks
>>>> Tiankun
>>>>
>>>>
>>>>
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>>>
>>>
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> 
> 
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