Re: Stop GRC flow graph after defined time

Dear Josh,

Your method below doesn’t work on GNU Radio v3.6.5.1
In this case, how to stop the flow graph in v3.6.5.1 …?

Thanks & regards,
activecat

Subject: Re: [Discuss-gnuradio] Stop GRC flow graph after defined time
Date: Wed, 29 Sep 2010 08:33:49 -0700
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.12)
Gecko/20100915 Thunderbird/3.0.8
You can use the Misc->Head block to limit the samples. Then set the flow
graph options to “run to completion”, this option is only available in
non-gui mode. See the options blocks.

-Josh

On 09/29/2010 04:31 AM, Thorsten Laude wrote:
Hallo,

I’m executing a flow graph in GRC and want to stop this flow graph
after some defined time, for example 3 seconds, or after a defined
amount of samples.

Currently I stop the flow graph by clicking on “Kill the flow graph”.
How can I implement, that the flow graph is stopped automatically?

Thorsten


Discuss-gnuradio mailing list
[email protected]
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio

http://lists.gnu.org/archive/html/discuss-gnuradio/2010-09/msg00420.html

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That run-to-completion method has never failed me; the only
explanation for that kind of behavior would be if your flowgraph
employed message passing. Is that the case?

Anyway, to make GNU Radio stop the flowgraph when your source is
empty, you shouldn’t call stop().
The source’s work() method returns the number of produced items. A
zero there should make the flowgraph realize you’re done. If you want
it explicitely (and right), let the work method return WORK_DONE (==-1).

Greetings,
Marcus

On 01.02.2014 13:57, Activecat wrote:

(X11; U; Linux i686; en-US; rv:1.9.1.12) Gecko/20100915
after some defined time, for example 3 seconds, or after a defined
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio

http://lists.gnu.org/archive/html/discuss-gnuradio/2010-09/msg00420.html

_______________________________________________ Discuss-gnuradio
mailing list [email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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Dear Marcus,

Thanks. This solves the problem completely.

In summary, to stop the flowgraph when the source is empty, we need to:
1). The source block’s work() method returns “WORK_DONE” ( which is -1
)
2). The sink block’s work() method returns “noutput_items”

Additional Questions:
1). In general, shouldn’t a sink block’s work() method always return 0
instead of “noutput_items”?
(Sink block doesn’t produce any output, isn’t the number of output
produced is zero?)

2). In practical cases, under what circumstances we should let the
source
block’s work() method return 0?
When it returns 0, the sceduler will still continue to call the
source
block’s work() method repeatly.

3). Under what scenario we will need to use the stop() method ?
(In python script we see stop() method quit often, but it seems
never
needed in c++ code)

Thanks.
activecat

Note:
This flow graph doesn’t involve any message passing at all.

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Hi Activecat!

On 02.02.2014 03:30, Activecat wrote:

Thanks. This solves the problem completely.
:slight_smile: Cool.

In summary, to stop the flowgraph when the source is empty, we need
to: 1). The source block’s work() method returns “WORK_DONE” (
which is -1 ) 2). The sink block’s work() method returns
“noutput_items”
Well, 2. is not really true.
To explain the mechanism (to understand better, maybe read about sync,
fixed ratio and general_work blocks in the wiki):

In normal operation, when a block downstream is finished with one
iteration of work, the scheduler knows how much items on its input
buffer have been consumed, determining the free space for the upstream
work(), since that work’s output is the same as the formers input
buffer, to avoid unnecessary copying.

So, if an upstream block says “hey, I’m done forever” (WORK_DONE),
then the scheduler knows that there is nothing new to do for the
downstream block.
It therefore continues to process the samples that are still in
buffers, until there are no blocks that could produce any output since
there is not enough input anymore.

So, in summary:

  1. yes,
  2. the downstream blocks are used as long as there is still work to do.
    Which of course will end fastest when they consume all their input
    items.

Additional Questions: 1). In general, shouldn’t a sink block’s
work() method always return 0 instead of “noutput_items”? (Sink
block doesn’t produce any output, isn’t the number of output
produced is zero?)
You should define your sink’s output IO signature to have an itemsize
of zero on all zero output streams. Since sinks are usually sync
blocks, there are as many output as input samples; if the former are
of size 0, then there are no buffers to shuffle around, though you can
still tell the runtime that you produced X samples, consuming X.

alternatively, return 0 and call “consume_each(X)” before.

2). In practical cases, under what circumstances we should let the
source block’s work() method return 0?
Never, unless you really can’t produce nothing. If your block is sync,
your flowgraph will start to stall.
When it returns 0, the sceduler will still continue to call the
source block’s work() method repeatly.
That sounds only right to me if downstream blocks don’t consume all
available buffer at once. The flowgraph will usually stop if a block
consumes 0 input items, since the runtime then assumes the block can’t
process anymore.

3). Under what scenario we will need to use the stop() method ? (In
python script we see stop() method quit often, but it seems never
needed in c++ code)
Wrong perspective: In Flowgraph code you often see start() stop()
since it is used to manage flowgraphs from a higher view.

inside work functions, you should never call stop(). Just say you’re
WORK_DONE, since you can’t say anything about the work in progress at
the rest of the flowgraph. Let the runtime manage shutting down the FG.

If your FG doesn’t contain message passing blocks (not even inside
hier blocks), the python main program will stop when it’s done, I’m
fairly certain. Can you share more about your flowgraph?

Greetings
Marcus
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Dear Marcus,

Thanks for thorough explanation.

Let me summarize the information, as below.
Correct me if I am wrong.

1). For sink block derived from gr::sync_block, its work() function
should
return noutput_items,
even though sink block doesn’t produce any output.
This is a norm.

2). We could opt to let the above work() function returns 0 instead of
noutput_items.
In this case it should call consume_each(noutput_items) before the
return.
All other remain the same, this should work.

3). Can we derive a sink block from gr::block ?
In this case we must explicitly call consume_each(noutput_items)
in
its general_work() function.
Should the general_work() return 0, or return noutput_items, or
either one will do?
The forecast() is defined to include
ninput_items_required[0] = noutput_items;

Question 1:
Sink block doesn’t produce any output, hence, noutput_items=0.
If this noutput_items has a non-zero value, what does this value means,
how
is it calculated?

Question 2:
Referring to
http://gnuradio.org/redmine/projects/gnuradio/wiki/OutOfTreeModules#Sources-and-sinks
it says that “Sources and sinks are derived from gr::sync_block”.
Why should sink block be categorised as sync block?
Sync block is defined as block that has the same number of input items
and
output items,
but sink block doesn’t fulfill this condition (sink block has no
output).

Regards,
activecat

Note:
My flow graph is very simple. It consists of only two blocks, namely a
source block and a sink block.
The source block sends out a series of integer numbers.
The sink block receives the integers, and print it out (std::cout).
Below is the code of the sink block.
Filename: gr-activecat/lib/integer_sink_impl.cc

namespace gr {
namespace activecat {

integer_sink::sptr  integer_sink::make()
{ return gnuradio::get_initial_sptr (new integer_sink_impl()); }

// private constructor
integer_sink_impl::integer_sink_impl()
  : gr_sync_block("integer_sink",
          gr_make_io_signature( 1, 1, sizeof(int) ),
          gr_make_io_signature( 0, 0, 0 ))
{ }

// virtual destructor
integer_sink_impl::~integer_sink_impl()
{ }

int
integer_sink_impl::work( int noutput_items,
          gr_vector_const_void_star &input_items,
          gr_vector_void_star &output_items)
{
    const int *in = (const int *) input_items[0];
    std::cout << "integer_sink receives: ";
    for (int i=0; i < noutput_items; i++)
        std::cout << in[i] << ", ";
    std::cout << std::endl;
    return noutput_items;  // Don't return 0, else the flowgraph 

won’t
stop even after the source block’s work() fucntion return -1
}

} /* namespace activecat /
} /
namespace gr */

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