Re: [Discuss-gnuradio] USRP1 problem, UHD problem, and one suggestion

[Brett L. Trotter]

Replying to self- here's another case on the USRP2/UHD-

TX Path: Sig Source -> UHD (USRP2) Sink

RX Path: UHD (USRP2) Source -> Band Pass Filter -> Scope Sink

It seems that any kind of filter, even with appropriate calculation of
the rate coming out of the filter taking into account decimation will
yield a very delayed signal on the scope sink. The same problem does not
happen on USRP1 when the sinks are swapped out and the sample rates
adjusted appropriately.


On 05/26/2011 07:29 PM, Brett L. Trotter wrote:
> USRP1:
> - When we have a very simple flowgraph with a USRP1 sink connected to a
> signal source and a USRP1 source connected to a WX scope- trying to shut
> down the app using the close box causes the USB on the host system to
> freeze up requiring a reboot. Yanking USRP power or ctrl+c'ing avoids
> this problem. This problem exists on many flowgraphs, both GRC generated
> and not- as far as I know it is limited to flowgraphs with both USRP1
> source and sink. This is a serious problem that has hit us on multiple
> platforms and machines and causes unnecessary reboots. It is honestly an
> unacceptable bug.
>
> USRP2 / UHD:
> - With a similar flowgraph to the one above, changing the secs/div
> causes the various traces to change phase relative to one another but
> this doesn't happen when a USRP1 source is substituted. However, I
> believe this is indicative of a deeper problem. We also see with the
> same flowgraph and a slider that controls both the TX and RX frequencies
> simultaneously, the flowgraph gets into a place where it seems to be
> getting data but it no longer represents the state of what's coming in
> and we also see the phase slippage. Long story short, create a flowgraph
> with a UHD (USRP2) sink and source with a siggen at a fixed
> frequency/amplitude, a wx scope, and a slider that sets the TX+RX
> frequencies to the slider value. Direct connect the TX to the RX with an
> SMA cable. Run the flowgraph and move the slider. At least on LFTX/RX
> this seems to give various results. Do the same thing with a USRP1 for
> comparison. To me it seems like UHD is losing data or the various paths
> in the flowgraph get out of whack with eachother. There were no O's or
> U's printed.
>
> We were trying to do a simple VNA in UHD and it just doesn't work as
> expected, but switching it all over to a USRP1 its fine and dandy.
>
>
>
>
> On a general note- I think there should be two new block sets added:
> 1) A simple source block that provides samples in the appropriate format
> (float, complex, etc depending on the _f / _c etc) which generates as
> fast as possible and counts how many it generates in a second which gets
> output on a float output.
>
> 2) The same thing but a consumer.
>
> The idea being it would help diagnose blocks that end up putting out
> more or less data than they take in and whose decimation/interpolation
> rates aren't apparent. For instance, I have a decimating filter block
> that appears to actually be producing more samples than it takes in,
> causing the data to show up almost 30 seconds later on the scope which
> is set at the source's data rate. I'd love to put the timed consumer and
> timed provider blocks on either side and see how the in/out amounts compare.
>
>
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