[USRP-users] b200 Overflows

Simon Brown simon at sdr-radio.com
Sat Sep 27 15:15:17 EDT 2014


Hi,

 

Thanks, that's invaluable information. I was wondering whether some of the
Ettus radios maybe supported 24-bit resolution, apparently not.

 

I'll try sc12 tomorrow and see what happens, currently running backups for
the rest of the evening.

 

Simon Brown G4ELI
http://v2.sdr-radio.com

 

From: Marcus D. Leech [mailto:mleech at ripnet.com] 
Sent: 27 September 2014 19:41
To: Simon Brown
Cc: usrp-users at lists.ettus.com
Subject: Re: [USRP-users] b200 Overflows

 

On 09/27/2014 02:30 PM, Simon Brown via USRP-users wrote:

Hi Marcus,

 

I'll try sc12 tomorrow, possibly later this evening. I'm currently preparing
food and adding some diagnostics.

 

It's probably in the manual, but is there a way to determine the most
efficient format for a device without losing resolution, for example sc12
for b200, (maybe) sc16 or fc21 for the N210 etc.? I would like to reduce any
network / bus traffic where possible.

 

Simon Brown G4ELI
http://v2.sdr-radio.com

The number of over-the-wire-formats is strictly-limited---it's not
open-ended.

For all products other than B200, the only available formats are sc16 and
sc8.   B200 has the additional sc12 over-the-wire format.

These "wire formats" are then converted by the driver into one of a few
host-side formats, the most natural for a lot of work being
  fc32.

The idea behind "wire formats" is to preserve a strictly-limited resource,
namely, over-the-wire bandwidth.  No amount of "buying the very best"
  1GiGe controller, for example, will get you beyond 1Gigabit of bandwidth
over that medium.  Which is why to support 50Msps on the N2xx, you
  have to use 8-bit wire format.    On the B200, you can reduce USB bus
bandwidth, but preserve ADC/DAC dynamic range by using SC12.  I think
  that only really "plays out" (normally) over USB-2.0.  Over USB-3.0, you
*should* have plenty of bandwidth available, at least over the USB-3.0
  bus and inside the controller.   But outside the controller, there may be
host-bus limitations that may drive on to using more
byte-per-second-conserving
  formats.





 

From: USRP-users [mailto:usrp-users-bounces at lists.ettus.com] On Behalf Of
Marcus D. Leech via USRP-users
Sent: 27 September 2014 19:11
To: usrp-users at lists.ettus.com
Subject: Re: [USRP-users] b200 Overflows

 

On 09/27/2014 02:00 PM, Simon Brown via USRP-users wrote: 

Thanks,

 

I've tried changing these, still get overruns with sample rates of 8MS/s or
higher.

 

Simon Brown G4ELI
http://v2.sdr-radio.com

 

Are you sure that your USB-3.0 interface is actually dealing with the device
as a USB-3.0 and not a USB-2.0 device?  

If you specify a wire-format of sc8 or sc12, do the overruns go away?  This
will help distinguish between cases involving CPU exhaustion, and interior
  bus deficiencies  (I found this on one of my embedded systems--could
sustain only 6.4Msps with full-width samples, but was perfectly happy to
  stream 12.8Msps with 8-bit samples).






From: USRP-users [mailto:usrp-users-bounces at lists.ettus.com] On Behalf Of
Marcus D. Leech via USRP-users
Sent: 26 September 2014 20:03
To: usrp-users at lists.ettus.com
Subject: Re: [USRP-users] b200 Overflows

 

On 09/26/2014 02:18 PM, Simon Brown via USRP-users wrote:

Hi,

 

Windows 64-bit: I'm streaming nicely, none of my threads indicate CPU
problems (plenty of headroom). At 8MB/s and higher I'm getting fastpath
Overrun messages every second or so even though I'm pulling data from the
b200 as fast as it's available, I am not CPU limited in any way. Using Intel
USB 3.

 

FWIW I don't see any way to tune the uhd::rx_streamer - bigger / more
buffers, also I don't see any way to flush either.

 

Interestingly if I get my CUDA card working harder (more work on the bus)
the Overrun messages appear more frequently. I7 4770k, good motherboard
(can't remember what).

 

Any suggestions?

 

Simon Brown G4ELI
http://v2.sdr-radio.com

 








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The USB transport parameters can be tweaked:

http://files.ettus.com/manual/page_transport.html#transport_usb_params





 
 
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-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org






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