Re: [Discuss-gnuradio] How to predict output buffer size

[Marcus Müller]

Hi Igor,

no, forecast() does **not** require your to predict the number of output
items.

It **gives** you a number of output items and a vector, into which you
fill in your **forecast of the necessary input items**:

Where's that documentation you're referring to? Maybe we have to improve
that!

anyway, I must admit that I don't understand what your block does. What
is a "sequence"?

Best regards,
Marcus
On 01/28/2017 07:03 PM, Igor Volodin wrote:
> Hi all,
>
> I am creating a block which will count number of "1" values in a
> sequence, and output it number (I am trying to convert PWM encoded bits).
> Block has 1 input (numpy.int32) and 1 output (it's also has
> numpy.int32 type)
>
> So, it should work following way:
>
> [1,1,1,0,0,1,0,0,0,1,1,1,1,1] -> [MyBlock] -> [3,1,5]
>
> Documentation says that i should predict number of output items in a
> forecast() method.  But i can't predict how many sequences will be in
> the input items.
> Could anybody suggest a solution for this case?
>
> Here is my Python code:
>
>
> import numpy
> from gnuradio import gr
>
> class hold_and_sum(gr.basic_block):
>     """
>     docstring for block hold_and_sum
>     """
>     def __init__(self):
>         gr.basic_block.__init__(self, name="hold_and_sum",
> in_sig=[numpy.int32], out_sig=[numpy.int32])
>         self.summary = numpy.int32(0)
>         self.in_accumulation = 0
>         self.out_bytes = [numpy.int32]
>
>     def forecast(self, noutput_items, ninput_items_required):
>         #setup size of input_items[i] for work call
>         for i in range(len(ninput_items_required)):
>             ninput_items_required[i] = noutput_items
>
>     def general_work(self, input_items, output_items):
>         in0 = input_items[0]
>         out = output_items[0]
>         for smpl in in0:
>             if smpl == 1:
>                 self.in_accumulation = 1
>                 self.summary = numpy.sum([self.summary, smpl],
> dtype=numpy.int32)
>             else:
>                 if  (self.in_accumulation == 1): #previous sample was 
> 1, and now we have 0, it's end of a pulse
>                     print self.summary # print pulse length
>                     self.out_bytes.append(self.summary)
>                     self.summary = 0 #empty counter
>                     self.in_accumulation = 0 #Reset flag
>         print self.out_bytes
>         if len(self.out_bytes) == 0:
>             self.out_bytes.append(0)
>         #out[:] = numpy.array(self.out_bytes) ???
>         del self.out_bytes[:]
>         #self.consume(0, len(input_items[0]))
>         self.consume_each(len(input_items[0]))
>         return (len(out))
>
>
>
> Best regards,
> Igor
>
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