[USRP-users] b200 Overflows

Simon Brown simon at sdr-radio.com
Mon Sep 29 11:58:00 EDT 2014


Hi Everybody,

 

Many thanks, this info is/was missing from the change log. Or maybe I’m just thick J .

 

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

 

From: Robert Kossler [mailto:Robert.D.Kossler.3 at nd.edu] 
Sent: 29 September 2014 15:09
To: Marcus D. Leech
Cc: Simon Brown; usrp-users at lists.ettus.com
Subject: Re: [USRP-users] b200 Overflows

 

Even after upgrade, sc12 only works with cpu format fc32 (not sc16).  So, if you want to use sc12, you need to choose fc32 as cpu format.

Rob

 

On Mon, Sep 29, 2014 at 10:04 AM, Marcus D. Leech via USRP-users <usrp-users at lists.ettus.com> wrote:

On 09/29/2014 03:00 AM, Simon Brown wrote: 

Marcus,

 

Using the 007.003.001 codebase uhd::stream_args_t(“sc16”, “sc12”) crashes inside usrp->get_rx_stream. I don’t see any reference to sc12 in the https://github.com/EttusResearch/uhd/blob/master/CHANGELOG, so I’m a bit lost now.

 

Please clarify (I’ve read the source) if I get an overrun then the data is being delivered from the B200 faster than the UHD.dll is reading it? If this is the case I also believe that there’s no way I can tell the underlying code to flush the LibUSB buffers?

 

I’m currently having considerable success with all Ettus hardware flavours but am a tad stuck with the whole UHD concept / way of life, your help is greatly appreciated.

 

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

http://files.ettus.com/manual/structuhd_1_1stream__args__t.html#aa54b7dc3e2c71d11c774d8b4a15984cc

Describes the components of stream_args_t.  In particular, the first component is the desired host-side ("CPU") format, the second the wire-side
  format.

I think sc12 was introduced after UHD 3.7.1, so upgrade.







 

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


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