Re: [Discuss-gnuradio] self.set_min_noutput_items() is not a valid python command in gnuradio ?

[Activecat]

Dear Marcus,

1). The line 299 of gnuradio-runtime/lib/block_executor.cc is:
      noutput_items = min_available_space(d, m->output_multiple(), m->min_noutput_items());

     If this line shows that set_min_output_items() works on the fly, does this also shows set_out_multiple() works on the fly?

     (just to confirm because I do not fully understand the source code).

2). Regarding the returning 0 issue, let me share my experience of experiments.

I am creating a custom interpolation block with its interpolation factor can be changed on the fly.  Hence it is inherited from gr::block.  It has one input port and one output port.

During runtime, there will be no problem if the general_work() return 0, provided it consume a non-zero value.

The flow graph may become unresponsive when the general_work() return 0 and consume zero.

My explanation:

Says, the instantaneous interpolation factor is 800. The general_work() is now called with noutput_items=699 and ninput_items[0]=3. In this case the only correct thing that general_work() should do is to consume 0 and return 0.

But later the general_work() will be repeatedly called again with the same arguments, i.e. noutput_items=699 and ninput_items[0]=3. In this case again the general_work() has to consume 0 and return 0.  This may repeat few thousand rounds, or infinite rounds. When this happens the flow graph becomes unresponsive (hang).

That's why it is important to set_min_output_items() to the instantaneous interpolation factor (which is 800), if the set_output_multiple() doesn't work on the fly.

If there is no better workaround, we have to stick to this trick at the moment.

Regards,

Activecat

On Fri, Mar 7, 2014 at 6:00 PM, Marcus Müller <address@hidden> wrote:

Hi Activecat,

to answer question 1):
grepping for "min_noutput_items" instantly shows that in gnuradio-runtime/lib/block_executor.cc line 299, your block's min_noutput_items() is called every iteration. If there isn't enough space, the block thread sleeps until there is more. So yes, it works on the fly.

I remember there was something with returning 0, and I know that producing 0 items used to mark a source as done, but this mechanism was commented out about a year ago (l. 483ff, I think for some good reason), but I can't remember that being an issue for a non-source block; have you tried it and did you run into problems?

Greetings,
Marcus

On 03/07/2014 02:26 AM, Activecat wrote:

Dear Sir,

Let me explain the reason of why to use the function: set_min_noutput_items().

I am creating a custom interpolator block. 

Says, the interpolation factor is 1000.  Hence it is important to call set_output_multiple(1000).

Meanwhile, for this block the interpolation factor depends on Sample Rate (samp_rate). In this flow-graph the samp_rate could be changed by the user during runtime. This means the interpolation factor may change during runtime, and hence we need to call set_output_multile() with different values during runtime !

The problem arisen when there is no guarantee that set_output_multiple() will work if you change it on the fly.

(Refer http://lists.gnu.org/archive/html/discuss-gnuradio/2010-11/msg00504.html)

The workaround is to use set_min_noutput_items() if it work on the fly.

Says, after changing samp_rate, the new interpolation factor is recalculated as 800.

If the set_output_multiple(800) doesn't work, the general_work() can still consume 1 input and produce 800 output if the noutput_items is at least 800. This enables the flow graph continue to work.

If the noutput_items is less than 800, the only correct thing the general_work() can do is to consume_each(0) and return 0. This may be problematic and can cause unforeseen behavior. So it is important to make sure the noutput_items is at least 800.  Hence I call:  set_min_noutput_items(800)

This means we can make use of set_min_noutput_items() as a workaround, if set_output_multiple() doesn't change on the fly.

The questions are:

1).  Can we use this to change setting on the fly:  set_min_noutput_items() 

2).  Is there any better workaround for this?

Regards,

Activecat

On Thu, Mar 6, 2014 at 11:36 PM, Tom Rondeau <address@hidden> wrote:

On Thu, Mar 6, 2014 at 2:12 AM, Activecat <address@hidden> wrote:
> Dear Sir,
>
> In c++ we have:  set_min_noutput_items()
> What is it equivalent syntax in python ?
>
> I try this:
>   self.set_min_noutput_items()
>
> Error message:
>   AttributeError: 'quadrator_upconverter_python1' object has no attribute
> 'set_min_noutput_items'
>
> Note:
> The self.set_output_multiple() in python seems accepted, is it functional
> ..?
>
> Regards,
> Activecat

Looks like when this feature was added, it didn't make it into the
block.i swig file. I'll push a patch for this soon.

But before you try and use this, be very careful. This is an advanced
issue that's really only meant to be used if you a) really really need
it and b) really really know what you are doing and why.

Tom

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