Re: [Discuss-gnuradio] Newbie wonders about latency

[Matt Ettus]

Quoting John Sidles <address@hidden>:

> Dear GnuRadio folks
>
> We at the University of Washington are quite interested
> to apply the Gnu Universal Software Radio Peripheral (USRP)
> as a nanomechanical device controller:
>
>     http://www.gnu.org/software/gnuradio/doc/exploring-gnuradio.html#usrp
>
> Basically, our task is to observe the complex amplitude
> of a MHz-carrier nanomechanical oscillator, then apply a
> controlling force that damps thermal oscillations.

Very interesting application!

> For this to work, the phase lag of the USRP processing
> chain
>
>
>      analog in ->
>        Rx daughterboard ->
>                 linear filter ->
>                      Tx daughterboard ->
>                                    analog out
>
>
> should be no more than about 100 microseconds.
> Is this kind of latency achievable?

Since you don't have a round-trip over the USB bus, there isn't much latency at
all.

I don't know how complex your "linear filter" is, but the rest of the stuff
should have a latency of significantly less than 1us.  More like in the 20-50
ns range.

The FPGA itself can be clocked at 128 MHz (or even 192MHz for small
computations), so that is what you should use to figure out the filtering
speed.

> Any advice you folks can give us would be *very* welcome.
>
>     Sincerely
>     John Sidles
>     http://courses.washington.edu/goodall/MRFM/


Thanks for your interest,
Matt