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Re: [Discuss-gnuradio] control of noutput_items by the user

From: Zing Yu
Subject: Re: [Discuss-gnuradio] control of noutput_items by the user
Date: Tue, 4 Dec 2012 10:04:03 -0800 (PST)

Hi Martin,

>to be fair, this problem is not what you asked for in your initial post.

You are right. I realized it only during my second post. Apologies for not being clear during the first time.

>A couple of notes:
>- The output buffer does not have to be "full" in order for the scheduler
>to call the following downstream block.

Good to know.

>- Undeterministic latency is one inherent problem of GNU Radio
>- 200 ms seems a bit much, though. Have you tried decreasing the buffer
>sizes between blocks? (Try set_max_output_buffer()).

So far, I have added the following line in the constructor of my custom block:
std::cout << max_output_buffer(0) << std::endl;
which returns -1. Does it mean some default value? If so, what is that value? Also, what is the range of value for 'size' in set_max_output_buffer(size)?

>- How many blocks are between your custom block and the UHD sink? Lots
>of blocks == lots of latency.

My flowgraph is the following:

uhd usrp source -> LPF -> my custom block -> uhd usrp sink

So essentially, there is no other block between my custom block and uhd usrp sink.

I have another question for you. I have now split the above flowgraph into two separate flowgraphs as following:
uhd usrp source -> LPF -> my custom block_1
my custom block 2 -> uhd usrp sink
where I have divided the functionality of my original custom block into custom block 1 and custom block 2. Now, when I relay the information from custom block 1 to custom block 2 by means of function probe, I get the error message AttributeError: 'gr_top_block_sptr' object has no attribute 'my_custom_block_1_0' which is expected (because the two flowgraphs are separate and independent). How can I pass the info from custom block 1 to custom block 2 in this case?


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