I was debugging a problem with a flowgraph when I realized that I wasn't getting the amount of samples I expected passing out of the USRP source block. If I set a sample rate too low, it tells me it has to set the sample rate to 0.125MSps. Currently I have a single stream from my source block, 30MHz clock rate, 500kHz sample rate.
If I run for 20 seconds streaming the data to a file (unbuffered set to off) as a complex, I would expect to see 20s * 8B * 500KHz = 80MB of data in the file. Instead, running it empirically (so the numbers will have to be ballpark and not exact), I see file size of 116153944. If I make the assumption that the sample rate was really 500kHz, that means it ran for 29.03s. This is obviously off by 50%. If I assume that 10s of data was really collected, that means I had an actual sample rate of 1.451924MSps. If I run these tests with the minimal 125kHz sample rate, I see things off by about double what I would expect. Moving my sample rate around the 1MSps range seems to work closer to what I expect, but of course I can't write files that fast without getting 'O' on the screen. Ultimately I need to use two receivers, so I don't believe that I can push the clock rate above 30.72MHz. I am running UHD-3_14 with RFNoC enabled (though I am not using RFNoC in this particular flowgraph). What am I missing here?
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