[USRP-users] b200 Overflows

Marcus D. Leech mleech at ripnet.com
Mon Sep 29 10:04:23 EDT 2014


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 <mailto: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 <mailto: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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>
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>
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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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