Re: [Discuss-gnuradio] USRP2 modulated signal tx error

[Ronaldo Nunez]

Hi Eric,
Thanks for your answer.
I will take a look at that. I'll work hard to patch it. I promise, I
need the USRP2 working fine as soon as possible.
When I finish I'll send it gnuradio the patch.

Thanks for all help.
Regards,

Ronaldo

2009/3/25 Eric Blossom <address@hidden>:
> On Tue, Mar 24, 2009 at 04:03:36PM -0300, Ronaldo Nunez wrote:
>> Hi folks,
>>
>> I tried to TX a FM modulated signal using USRP2 BasicTX.
>> The signal was a 440 Hz sinusoid, and the carrier 1 MHz.
>> I used the signal generator and fm modulator blocks provided by GNURadio.
>>
>> When I tx it the follow message appeared on the screen:
>>
>> USRP2::Tx_RAW: FIXME: short packet: 1 item (32 bytes)
>>
>> Sometimes the item number changes to 4 or 8...
>> What that mean?
>>
>> I took a look at the usrp2_impl.cc (last revision) and i couldn't
>> identify any problem...
>>
>> Any suggestion is welcome.
>> Regards,
>>
>> Ronaldo
>
> Hi Ronaldo,
>
> There's a bug in the on-the-wire format for the USRP2 where we're not
> currently transmitting the valid length of the packet.  With ethernet,
> the minimum packet size is 64-bytes, and there are some times where
> the host code is naively fragmenting the received samples in a way
> that produces a packet that is too short for ethernet.
>
> I've opened ticket:378 on this.  It will be properly fixed when we
> rework the on-the-wire format as part of the VRT work, but I think
> there's an intermediate step that can avoid most cases of the problem
> happening.  I'm not sure that I can find time to fix this in time for
> 3.2.0, but if you'd like to take a look at it, we'd love a patch for
> it.  What needs to happen is that the loop in usrp2_impl.cc(tx_raw)
> that fragments the nitems items needs to be a little smarter about
> breaking the items into ethernet frames.  Each piece needs to be
> between 9 and U2_MAX_SAMPLES samples long.  (9 works out to the
> smallest number of samples that plus the headers ends up being >= 64
> bytes).
>
> Eric
>



-- 
__________________________________
Ronaldo A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil