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Re: [Discuss-gnuradio] (Python) Source Block Outputs All 0's

From: David Halls
Subject: Re: [Discuss-gnuradio] (Python) Source Block Outputs All 0's
Date: Tue, 18 Feb 2014 22:11:43 +0000

Hi Nathan,

Thanks for your reply :)

I've done little python before, am trying to incorporate a collaborators code into my system and he's used python.

I am used to C, where it would copy the pointer. I understand your advice - thanks, I will look at the link.

The return value is mimicking the WORK_CALLED_PRODUCE (-2) and WORK_DONE return values that can be used when you have multiple outputs which may output different number of items and the produce function is used.

I am not sure why the block keeps repeating if I use -2 as I use successfully in many c++ blocks - I'm not used to writing source blocks... maybe others have comments?

From: West, Nathan address@hidden
Sent: 18 February 2014 21:06
To: David Halls
Cc: GNURadio Discussion List
Subject: Re: [Discuss-gnuradio] (Python) Source Block Outputs All 0's

On Tue, Feb 18, 2014 at 12:50 PM, David Halls
<address@hidden> wrote:
> Hi All,
> I have implemented a python source block:
> def __init__(self, kA1=4,kB1=4,k2=4,NA1=8,NB1=8,N2=8,M=8):
> gr.sync_block.__init__(self,
> name="blsd_enc_b",
> in_sig=None,
> out_sig=[numpy.uint8,numpy.uint8])
> but I can't get it to output anything but 0's....
> def work(self, input_items, output_items):
> out_cA = output_items[0]
> out_cB = output_items[1]
> out_cA = [ 5, 6, 7, 8, 9, 10 ] #cA[0]
> out_cB = [ 5, 6, 7, 8, 9, 10 ] #cB[0]
> self.produce(0,len(out_cA))
> self.produce(1,len(out_cB))
> print 'out_cA = ', out_cA, ', len(out_cA) = ', len(out_cA)
> print 'out_cB = ', out_cB, ', len(out_cB) = ', len(out_cB)
> return -1 #-2
> I connect both outputs to a file sync of type byte, and it stores 6 bytes
> but its all "\00\00\00\00\00\00"
> The print lines give:
> out_cA = [5, 6, 7, 8, 9, 10] , len(out_cA) = 6
> out_cB = [5, 6, 7, 8, 9, 10] , len(out_cB) = 6
> as expected.
> Any advice?
> Regards,
> David


The problem here is that you're not inserting items in to the out_cA
(and out_cB) arrays, you're actually reassigning out_cA to be this new

Honestly, I've never written a python block, but my understanding is
that you'd have to do something like this http://dpaste.com/1634971/

The items in the out_items list are actually numpy arrays, and they
need to be indexed. The [:] indexing is a shortcut of indexing the
entire array.

Another thing I'm not really sure about is whether the -1 will work or
not. I think you might have to return 6 so that the scheduler knows
there are 6 items to work on, and then the next time work is called
you return -1 ( assuming you're wanting to stop the flowgraph here?).
Somebody else might chime in here if I'm wrong.



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