Re: [Discuss-gnuradio] Reading from USRP

[Timur Alperovich]

> 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.

Thank you Stefan. That definitely explains it! What is the
advantage/reason for using the inband firmware? I was working on
adapting some of the OpenBTS code for what I'm trying to do and I
didn't realize they're using the inband firmware and didn't realize
the differences in the data returned by the different firmware.
Searching gnuradio.org, I couldn't find anything on the wiki about it.

> 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

-- 
Cheers,
Timur