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[Discuss-gnuradio] timestamp tags and set_min_output_buffer


From: Juha Vierinen
Subject: [Discuss-gnuradio] timestamp tags and set_min_output_buffer
Date: Wed, 9 Oct 2013 14:59:20 -0400

Hi,

I'm writing a block that always outputs the same number of items as it gets in. 

The block is doing FFT on a fixed length vector, so I always need nfft samples in and nfft samples out. I've achieved this (I think) by using: set_min_noutput_items(nfft) and set_max_noutput_items(nfft). However, when I increase nfft to 8192, I get a message about not enough buffer space. I tested various things and ended up calling  
set_min_output_buffer(2*nfft)  as just nfft wasn't enough. It all seems to work nicely, except that the rx_time tags are screwed up -- I get a nearly random offset in the beginning, even though there are no dropped packets on the USRP. 

Is this a bug or a feature? What is the correct way to increase the value of noutput_items without breaking rx_time tags?

juha

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