Re: [Discuss-gnuradio] Constant output message source

[ichigo.san]

Cool thanks for the reply.

The reason I am doing this is because I am trying to transmit signals at
different times... and testing shows the interleave block acts like the sync
type blocks you mention. I am guessing the same idea can be applied and make
a new interleave block and inherits from the gr_block.

Though I am just wondering that this has to be a common problem with the
dual usrp TX usage, I was wondering if anyone else has done similar work
already or has an more "standard" solution using the tools already built
into GNU radio. As I am not too familiar with the build toolchain and the
C++ backbones behind the python, however I will be reading up on it now.




Tom Rondeau wrote:
> 
> On Sat, Feb 19, 2011 at 4:52 AM, ichigo.san <address@hidden> wrote:
> 
>>
>> Hi,
>>
>> I was wondering if there is a method to have a source block constantly
>> sending out "0" and once it recieves a message from python, e.g a packet,
>> it
>> will then stream the message and switch back to sending "0" when done.
>>
>> I've tried:
>> Message Source ----------------------------> (Add, 0)
>> Constant Source/Vector Source with 0 -----> (Add, 1) ---> output
>>
>> However, the add block (and all blocks in gnuradio) waits for stream
>> items
>> from both inputs to be ready (i.e no interpolation) before making a
>> output
>> stream item. This effectively nullifies the const source in the above
>> example.
>>
>> I was wondering if there is any possible way to solve this problem?
>>
>> The reason I am asking this is I am using a dual TX setup on a single
>> USRP
>> which interleaves output signals. I have I output signal that is
>> constantly
>> sending (beacon) and one that is only sending sometimes, however the
>> interleaving of output signals means that both streams needs to be
>> constantly sending.
>>
> 
> Right, the add block needs to see items from both streams so that it can
> add
> them together. If there is no data on one stream, there is nothing to add
> and it does not assume zeros.
> 
> My advice is to make a new block. The easiest would probably to make a new
> add block that inherits from gr_block instead of gr_sync_block. In this
> block, you tests the length of both inputs and add which items together
> that
> you want, substituting zeros when there is no more data on the incoming
> message stream. It will be pretty specific to your needs, and be careful
> with your consume() and return item numbers to account for what you've
> done
> with both streams.
> 
> Tom
> 
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> 

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