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Re: [Discuss-gnuradio] Can a tagged stream block be a source block?

From: Martin Braun
Subject: Re: [Discuss-gnuradio] Can a tagged stream block be a source block?
Date: Thu, 04 Dec 2014 16:08:28 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0

On 12/04/2014 02:17 PM, David Marmoy wrote:
> I am implementing a complete protocol in a module where most of the MAC
> layer will be placed in a tagged stream block. I intend to start out
> implementing the transmit chain and then the receive chain. 
> The problem I have run into is that until I get to the receive chain,
> the MAC layer block will need to function as a source, but is that at
> all possible based on a tagged stream block? 

Short answer: Erh, maybe. But not without changing the runtime.

Long answer: This a known shortcoming of tagged stream blocks. For 3.8,
we will most likely be changing the structure of those blocks, and this
will become possible.

Right now, we could update the code in tagged_stream_block to make this
happen, but it would involve more testing and branches in the work
function. It would not be a big problem to fix, though, you're just the
first to actually request this.

Actually, it's probably something I should fix before people start
writing tags by hand. David, until I have that ready you should change
that offending line to:

102     if(!d_n_input_items_reqd.empty() && d_n_input_items_reqd[0] ==
0) { // Otherwise, it's already set from a previous call

parse_length_tags() will then never be called.
calculate_output_stream_length() however should return a valid length.


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