[USRP-users] Rx/Tx Loopback

mleech at ripnet.com mleech at ripnet.com
Thu Apr 2 10:51:48 EDT 2015


Well, I wonder if our gr-uhd maintainer has a comment. 

This seems very odd to me, and perhaps there's a subtlety in the way
gr-uhd tries to be helpful and setup a bunch of stuff involving sample
timing automatically. 

On 2015-04-02 10:28, Rob Kossler wrote: 

> On Wed, Apr 1, 2015 at 11:45 PM, Marcus D. Leech <mleech at ripnet.com> wrote:
> On 04/01/2015 11:41 PM, Rob Kossler wrote: 
> Yes, those are the sync options. Since there is only one device, I only selected "unknown PPS" for one of the two streamers. Is that correct? 
> Rob
 That would be correct for a device that had 1PPS. I don't recall
whether X3xx has a "fake" internal 1PPS signal or not. Since this is a
single device
 at this point, just choose "don't sync" for both of them. 

I tried "don't sync" for both as well as putting constant multiply
blocks in between the source / sink. Neither seems to fix my "Late"
issue. However, if I exit GRC and simply run benchmark_rate in full
duplex, it has no issues even at higher sample rates.

Attached are 3 files: the modified GRC flowgraph as well as two text
files showing the results obtained when running this flowgraph from GRC
as compared to running benchmark_rate. The flowgraph sample rate is 1
MS/s while the benchmark_rate is running at 10 MS/s (BTW, it also runs
fine at 1MS/s).


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