[USRP-users] sampling rate issue

Michael Dickens michael.dickens at ettus.com
Fri Jan 24 10:43:30 EST 2020

Hi Massoud - The 'O' and 'U' mean overflow and underrun, respectively; see
also:< https://files.ettus.com/manual/page_general.html#general_ounotes >.
Note that if the O/U occur regularly during runtime they -will- impact data
flow; these are best avoided! Any that occur during flowgraph startup or
shutdown can generally be ignored.

Whether your B210 can support bi-directional 10 MS/s or 20 MS/s or 28 MS/s
depends on a number of factors, such as the quality of the USB cable, the
USB chipset in the host computer, the general speed / power of the host
computer to do CPU-based processing, and whatever application is generating
(for Tx) and/or processing (on Rx) the data.

Since you're using GNU Radio, the actual flowgraph you're executing impacts
the max supported throughput: UHD will generate a 'U' for underrun on Tx if
the host computer isn't supplying data fast enough to UHD (and thence to
the USRP), and an 'O' for overflow on Rx if the host computer isn't
consuming data fast enough from UHD (and thus from the USRP). A faster
computer might help here, but a "better" flowgraph might also do the trick.

You can test out pure-UHD (no GNU Radio or anything else) Tx, Rx, or Tx/Rx
max rates for your setup via the UHD "benchmark_rate" example; for example:
"benchmark_rate --rx_rate 2e6 --tx_rate 2e6" will test simultaneous Tx and
Rx at 2MS/s each way. In this manner, you can figure out what the max rates
supported by your setup are.

On my setup, I can get 28 MS/s bidirectional without issues; my setup is a
2019 8-core MacBook Pro with USB-C, and the cable is high quality ... so
I'm confident my overall computer setup is very capable!

If, after testing with just UHD, your system can't support the your desired
28 MS/s bidirectional, then you should explore (1) a better USB cable,
since they are relatively inexpensive; and then (2) a better host computer.
If testing with just UHD shows good throughput, then it's a GNU Radio issue
and you should explore a better GNU Radio flowgraph (whatever that might
mean for your specific needs here).

Hope this is useful! - MLD

On Fri, Jan 24, 2020 at 3:00 AM massoud pourmandi via USRP-users <
usrp-users at lists.ettus.com> wrote:

> Dear colleagues,
> Based on the USRP B210 datasheet, I can increase the sampling rate of the
> device to 28 MS/s if I use RFA (TX/RX, RX2) ports simultaneously as
> transmitter and receiver, respectively. Thought, for sampling rate greater
> than 2MS/s, I start getting messages at the output terminal. I attached the
> messages in the following.
> First: theses ‘O’ and ‘U’ signs, what are the meanings of these signs?
> Second: I need to be able to use the highest sampling rate of B210, should
> I have to use a more powerful PC?
> I would appreciate if you explain the solutions of this issue in more
> detail.
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

Michael Dickens
Ettus Research Technical Support
Email: support at ettus.com
Web: https://ettus.com/
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