Re: [Discuss-gnuradio] about USRP2_MIN_RX_SAMPLES

[Mattias Kjellsson]

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"). 
>
> 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?)
>
>   
I think it had something to do with 371items*4bytes = 1484 bytes. I 
think it was excluding the header, which I can't remember the exact size 
of on top of my head. But I have a feeling that the size of a packet was 
1498 bytes or so. I have a feeling that I sent a code- snippet to Eric 
Blossom last summer which read/re- wrote the MTU of the NIC, but as he 
pointed out, the code should work on a whole bunch of platforms and 
systems. The code should work in most cases, since MTU=1500 is more or 
less standard, except some odd cards which have 1400 bytes MTU.

I think it was set to 371 in order to minimize overhead.

//Mattias