Re: [Discuss-gnuradio] timed dual channel B210 capture gives error "UHD source block got error code 0x2" (ERROR_CODE_LATE_COMMAND)

[Marcus D. Leech]

On 02/22/2015 04:26 PM, Martin wrote:
> Small addition.
> I just want to start capturing on both channels of a B210 at the exact 
> same time. I do not mind which time that is, as long as the samples 
> are aligned.
>
> I have read a discussion on this mailinglist which made it clear that 
> you do need to set a start_time (timed_capturing) with dual-channel 
> capturing with a B210 to have both channels synchronized.
> You should not set the internal B210 clock with set_time_now, since 
> this would set a slightly different time in the two different channels.
> This would then result in a random clock misalignment betwen the 
> channels of up to 250 usec.
>
> it was advised to use set_time_unknown_PPS or leave the time at the 
> default internal initiated time. This way both channels should have an 
> aligned internal clock.
>
> Then using a start_time in the near future should result in perfectly 
> aligned captures. But as I said in my previous mail, this results (for 
> me) in the UHD error.
> "UHD source block got error code 0x2"
>
>
> Martin
I use a GR flow-graph to do this for interferometry, without having to 
specify anything special.

I use a subdev spec of "A:A A:B"  and specify two channels in the source 
block.  Everything lines up nicely.  You might look at the code that
  situation generates if you're hand-coding.


> On 22-02-15 21:53, Martin wrote:
> > When you start a dual channel timed capture in the near future with a
> > B210, the work method of usrp_source_impl.cc prints out
> >
> > "UHD source block got error code 0x2"
> >
> > error codes are defined in:
> > metadata.hpp line 99:
> > //! A stream command was issued in the past.
> > ERROR_CODE_LATE_COMMAND = 0x2,
> >
> > No matter what starttime (in the future) was chosen, UHD always thinks a
> > command is scheduled to be run in the past (too late)
> >
> > When I do the same with a single-channel script on the same B210
> > everything works fine without errors.
> >
> >
> > The dual channel always prints out the error, and the single channel
> > always seems to work fine.
> > I have tried different settings for the delay, which sets how long in
> > the future the capture is set to start.
> > But 0.1 0.2 1.0 2.0 5.0 seconds all seem to fail.
> >
> > I also tried with or without using 1 PPS to set the clock time, but that
> > did not help either.
> >
> > code snippet:
> >
> > usrp_source_impl.cc
> > line 663:
> > switch(_metadata.error_code) {
> > ...
> > line 692:
> > default:
> > std::cout << boost::format("UHD source block got error code 0x%x")
> > % _metadata.error_code << std::endl;
> > return num_samps;
> >
> >
> > I created an issue on gnuradio.org and attached example python scripts
> > there to demonstrate the error. Dual channel script fails, single
> > channel works.
> > http://gnuradio.org/redmine/issues/769
> > The defaults are fine for demonstrating the behaviour so you do not need
> > to give any arguments.
> > Note that I used a B210 with an embedded GPSDO, which might be 
> > important.
> >
> > It is also very possible that I am doing something very wrong.
> > Please let me know.
> >
> >
> > With best regards,
> >
> > Martin Dudok van Heel
> >
> > _______________________________________________
> > Discuss-gnuradio mailing list
> > address@hidden
> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>
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