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

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
>>
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>> Discuss-gnuradio@gnu.org
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>
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