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Re: [Discuss-gnuradio] about USRP2_MIN_RX_SAMPLES

From: Ulrika Uppman
Subject: Re: [Discuss-gnuradio] about USRP2_MIN_RX_SAMPLES
Date: Wed, 16 Sep 2009 10:46:29 +0200

Thank you both Mattias and Eric for your replies!

However, I believe you are talking about the U2_MAX_SAMPLES and U2_MIN_SAMPLES 
defined in usrp2_eth_packet.h. So, is this U2_MAX_SAMPLES the same as the 
USRP2_MIN_SAMPLES since they are both set to 371 (but the later is not changed 
to 370 in later rev), or is USRP2_MIN_SAMPLES not used at all?


-----Ursprungligt meddelande-----
Från: Eric Blossom [mailto:address@hidden 
Skickat: den 15 september 2009 20:23
Till: Ulrika Uppman
Kopia: GNU Radio Discussion
Ämne: Re: [Discuss-gnuradio] about USRP2_MIN_RX_SAMPLES

On Tue, Sep 15, 2009 at 04:41:39PM +0200, Ulrika Uppman wrote:
> Hi all!
> I ran into the constant USRP2_MIN_RX_SAMPLES = 371 defined in 
> usrp2_base.h, but I don't get what it is used for (it comes with the 
> comment "BIG ASS FIXME: get from lower layer MTU calculation").

I believe you're referring to USRP2_MAX_RX_SAMPLES.  It's the largest number of 
samples that will fit in a 1500 byte ethernet packet including overhead.  The 
constant sizes some structures.  (BTW, it was recently adjusted downward to 370 
samples to ensure alignment for dual channel apps).

> Does anyone know anything about this constant and what it affects? 
> ... what is depending on that it has the value 371?

> (I got seg faults when trying to run less than 371 items out of a
> USRP2 source block, I believe this constant has something to do with 
> that perhaps?)

How we're you trying to do this?  Hint: don't change the constant.

We don't currently expose this in the gr-usrp2 interface.

We do expose it in the usrp2::usrp2::start_rx_streaming interface.
items_per_frame = 0 gets you the default (currently 370 or 371 depending on 
rev).  You can set it lower if you like.
usrp2_source_base::start currently passes 0 to get the default.


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