[USRP-users] b200 Overflows

Simon Brown simon at sdr-radio.com
Mon Sep 29 12:50:30 EDT 2014


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).

 

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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