Re: [Discuss-gnuradio] Reading from USRP

[Stefan Bruens]

On Sunday 12 July 2009 08:09:24 Timur Alperovich wrote:
> Hey guys,
>
> I've been trying to read from the USRP by simply doing u->read(buf,
> 512, overrun). I used the usrp_inband_usb_packet class to extract the
> payload size and the payload from each USB packet received. As I
> understand, the USB packets contain pairs of I and Q for each (I
> didn't change the format from the default). I was expecting the
> payload size then to be a multiple of 4, since it is 2 shorts. I
> frequently see payload sizes such as 7, 13, etc. What is going on
> here? Are there examples of getting the data from a dbsrx using this
> method and processing it? I found the test_standard_rx example, but it
> doesn't do any processing and just reads.

If you want to use the inband code, of course you have to use the inband 
firmware as well. Most probably, you use the standard firmware, and the 
"payload size" you see is a normal sample.

USB packets produced by the standard firmware always contain 512 bytes/128 
complex samples (as long as you stick to standard sample resolution of 16 bit 
per component).

The inband firmware will produce packets containing 504 bytes of payload (126 
samples), and it will accept shorter packets.

Regards,

Stefan

-- 
Stefan Brüns  /  Bergstraße 21  /  52062 Aachen
phone: +49 241 53809034     mobile: +49 151 50412019