Hi Vladimir, exactly! So, if you directly write to a file from the USRP Source, then don't use float – there's no more information in the floating point numbers than in the 16 bit integers. But if you need to do mathematical operations on the samples, it's usually helpful to have them in float.
Best regards, Marcus On 08/29/2017 08:23 PM, Vladimir Rytikov wrote: > Marcus, > > I see your point. In GNU Radio flow chart when you instantiate USRP > source - you can set out put datatype. The default is complex float - > two floats per sample which is 4*2=8 bytes. you mentioned on USB wire > we got 2*2 bytes per sample = 4 bytes per sample. so we got double > data rate coming out of USRP sink when we process it in GNU Radio. if > we have 20 MHz sample rate we got 20*4 = 80 MB/s data rate coming out > device. and we got 160 MB/s coming out of USRP Source to the > filesystem. Does it make sense ? > > -- Vladimir > > On Tue, Aug 29, 2017 at 11:15 AM, Marcus Müller > <[email protected] <mailto:[email protected]>> wrote: > > Hi Vladimir, > > because you're mentioning "float", what you're referring is the > data type on the host, ie. what UHD converts the data that comes > in through USB to. > > On the USB cable itself, there's already signed 16 bit integer > complex, by default. > > Yes, you can further reduce that (change the "OTW" data format to > sc12, sc8, whatever your device supports), but it of course > reduces dynamic range / increases quantization noise, so you > normally wouldn't want to do that. > > You do that by using an appropriate stream_args_t [1] when getting > the RX streamer. In GNU Radio Companion, you simply select the > other OTW format in the drop down menu labeled "Wire Format". > > Best regards, > > Marcus > > [1]https://files.ettus.com/manual/structuhd_1_1stream__args__t.html > <https://files.ettus.com/manual/structuhd_1_1stream__args__t.html> > > > On 08/29/2017 08:08 PM, Vladimir Rytikov wrote: >> will it help to change data type from float to complex16 to >> reduce data rate ? >> >> On Tue, Aug 29, 2017 at 11:02 AM, Marcus Müller via USRP-users >> <[email protected] <mailto:[email protected]>> >> wrote: >> >> 20 MS/s is already 80 MB/s, which is 0.64 Gb/s. It's not that >> little data to shuffle around! So you already need a halfway >> decent USB3 setup to do that. Also, your computer mustn't be >> very slow. What is your computer, in fact? >> >> Best regards, >> >> Marcus >> >> >> On 08/29/2017 05:07 PM, Cho, Daniel J (332C) via USRP-users >> wrote: >>> >>> Hello – >>> >>> >>> >>> I am having issues with overflow with the USRP B210 at 20 >>> MSPS. I am using a LiveUSB that has Ubuntu and Gnuradio in >>> it. The gnuradio flow chart is just the USRP source going >>> into a file sink with the destination being just /dev/null. >>> Since the data is going to /dev/null, there should be no >>> reason for an overflow to occur but for some reason, I get >>> one or two about every 10 seconds. >>> >>> >>> >>> Thanks, >>> >>> Daniel Cho >>> >>> >>> >>> _______________________________________________ >>> USRP-users mailing list >>> [email protected] <mailto:[email protected]> >>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com> >> _______________________________________________ USRP-users >> mailing list [email protected] >> <mailto:[email protected]> >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com> >> >>
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