Re: [Discuss-gnuradio] UHD Announcement - July 6th 2010

[Zohair]

Hi Josh,

Just a quick note. I don't use ctrl+c to kill the graph. Instead I use the
kill button ( or F7).. Thanks again for the info provided.

Regards,

Zohair

Josh Blum-2 wrote:
> 
> 
>> It's working now! I changed it to 50ms instead of 10 and added the lines
>> in
>> the synchronisation for loop in mimo_usrp.cpp to see the amount of
>> deviation
>> between usrps if they are synchronised:
>>
>> float diff=(time_i.get_real_secs() - time_0.get_real_secs())*1000;
>> std::cerr<<  boost::format("Time was reset successfully for board %d with
>> deviation: %f ms relative to board 0")
>> % i %diff<<  std::endl;
>>   The output is:
>> Set time with unknown pps edge:
>>      1) set times next pps (race condition)
>>      2) catch seconds rollover at pps edge
>>      3) set times next pps (synchronously)
>> Time was reset successfully for board 1 with deviation: 1.095390 ms
>> relative
>> to board 0
>> Time was reset successfully for board 2 with deviation: 1.093340 ms
>> relative
>> to board 0
>> Time was reset successfully for board 3 with deviation: 1.096530 ms
>> relative
>> to board 0
>>
> 
> Your seeing the RTT between requests for the timestamp, since it is 
> working, the actual deviation is 0 and your boards are synced.
> 
> Thats why the test above is really just a sanity check to ensure that 
> the boards are not too far off (which otherwise implies that the 
> synchronization failed).
> 
>> However, I still have a few questions:
>> 1-Can't we make the deviation exactly zero? What factors affect this?
>>
>> 2- In my tries to run the flowgraphs, sometimes I receive these errors:
>> OError (usrp2 recv pirate loop): assertion failed: if_packet_info.has_tsi
>> and if_packet_info.has_tsf
>>    in void
>> usrp2_impl::io_impl::recv_pirate_loop(boost::shared_ptr<uhd::transport::zero_copy_if>,
>> boost::shared_ptr<usrp2_mboard_impl>, size_t)
>>    at /home/dave/uhd/host/lib/usrp/usrp2/io_impl.cpp:106
>>
>> you told me before it's save to neglect these errors but when i neglect
>> them
>> I receive rubbish data not what I am expecting, despite the fact that
>> boards
>> indeed synchronised. These errors disappear when I power cycle the USRPs.
>> Is
>> there anything I can do about this?
>>
> 
> If the setup does not shut down properly, some boards may be left 
> streaming. When a board begins to receive again, it may get partial 
> packets and recognize them as junk. You can ignore the warnings.
> 
> When you close the flowgraph does the application exit nicely or do you 
> have to control+C?
> 
> personal todo list: clean out the udp recv buffer chain on initialization
> 
>> 3- Also, sometimes a number of "O" characters get printed on the screen,
>> what does this mean?
>>
> 
> overflow, in the case of the usrp2, there is overflow in the socket 
> buffer, packets are dropped, and the uhd driver noticed a discrepancy in 
> the progression of sequence numbers and prints "O"
> 
>> 4- What is the least sampling freq that I can use?
>>
> 
> actual sample rates achievable by the hardware are 100e6 divided by 
> //_USRP2_RATES = range(4, 128+1, 1) + range(130, 256+1, 2) + range(260, 
> 512+1, 4)
> 
> so the smallest rate is 100e6/512 = 195312.5 Hz
> 
>> I am so glad that we have got something working now and Thank you very
>> much
>> indeed.
>>
> 
> glad to hear it too, i will fix the mimo source with a timeout 
> proportional to the number of channels
> 
> -Josh
> 
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> 

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