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Re: [Discuss-gnuradio] Scheduling a block even with no input items RE: F


From: Martin Braun
Subject: Re: [Discuss-gnuradio] Scheduling a block even with no input items RE: Flow graph blocking when doing 2x1 transmission
Date: Tue, 03 Jun 2014 16:25:04 +0200
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On 06/03/2014 03:59 PM, David Halls wrote:
> Hey Martin,
> 
> Good to hear from you as always. Gnuradio scheduling baffles me more
> than anything else on this planet. The day I get my head around it will
> be a happy day indeed. :0

Some things aren't meant for us mere mortals :)

> The problem with using 'sob', 'eob' is because I have two inputs to the
> USRP UHD sink. One is constantly transmitting and has items coming in
> from time=0, but the other has no input items from time=0, they only
> arrive later on. As a result the sink seems to block waiting for items
> on *both* inputs before it will transmit anything. I don't want the USRP
> to have to wait for the second stream to be populated before it
> transmits anything...

Hm, this is an interesting use case I think we might want to address at
some point. But this doesn't help you right now.

> I thought 'forecast' may help me out, but wasn't sure what to put in the
> function to make it schedule even when there are no input items?

Haven't tried this, but maybe you can just tell it that
ninput_items_required = 0 for some values of noutput_items.

Again, this might produce too many zeros. Maybe you need something more
sophisticated.

Cheers,
Martin

> 
> David
> 
> -----Original Message-----
> From: Martin Braun [mailto:address@hidden
> Sent: 03 June 2014 14:53
> To: David Halls; address@hidden <mailto:address@hidden>
> Subject: Re: [Discuss-gnuradio] Scheduling a block even with no input
> items RE: Flow graph blocking when doing 2x1 transmission
> 
> On 06/03/2014 03:30 PM, David Halls wrote:
>> Dear All,
>>
>> Had anyone tried to implementing a gnuradio block that will output
>> zeros if there are no items at the input, and will simply copy the
>> input to output otherwise?
>>
>> I find that if there are no items at the input, the block never gets
>> scheduled.
>>
>> I want this block to feed zeros to my USRP until actual data is ready
>> to be passed to it.
> 
> Hey David,
> 
> any reason you can't use eob/sob?
> 
> Also, did you set forecast accordingly?
> 
> Note that this can go wrong easily: If this blocks produces a bajillion
> zeros very quickly, nothing will happen until the USRP has consumed them
> all.
> 
> M
> 
> 
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