[USRP-users] b200 Overflows

Marcus D. Leech mleech at ripnet.com
Mon Sep 29 12:53:27 EDT 2014


On 09/29/2014 12:50 PM, Simon Brown wrote:
>
> Ah,
>
> So -- is this overrun on the B200 itself or as I assumed inside the 
> UHD.dll's own buffering? If it's inside the B200 then it would 
> possibly be firmware?
>
> Apart from this overrun and something bloody odd errors with USRP1 on 
> USB3 I am, at the moment, a happy camper (I'll report these errors later).
>
USB-3 controllers very-often aren't happy "downshifting" to support 
USB-2.0 devices.  The USRP1 may just be one of those.   I've found the same
   with the RTLSDR dongle devices as well--they *don't work* on a 
USB-3.0 port.


> Ian -- everything helps, I do understand hardware, it's what people 
> buy. Software on the other hand is assumed to be free...
>
> Simon Brown G4ELI
> http://v2.sdr-radio.com
>
> *From:*Ian Buckley [mailto:ianb at ionconcepts.com]
>
> Simon,
>
> Just to give you the H/W picture, you can visualize Rx data in the 
> B200 as flowing through the following in order:
>
> DSP->Packetization Logic-> FIFO's
>
> There actually quite a few FIFO's before the USB interface is reached 
> and they all run (in H/W) much quicker than USB3 throughput.
>
> Thus data "falls through" and tends to accumulate at the last FIFO(s) 
> where it is rate limited by whatever the USB performance is.
>
> If the sustained USB throughput (over a significant period of time) 
> can't match the sample rate (rate over the USB wire...DSP output rate) 
> then that chain of FIFO's slowly fills and, when the packetization 
> logic can not add any more samples to the head of the FIFO chain then 
> and overflow error indication is signaled to the host in an error 
> packet (that bypasses the queued sample data).
>
> Not directly helpful for you I know, but always nice to have the big 
> picture.
>

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