USRP2 latency calculations


#1

I foud this wery usefull:
http://www.gnuradio.org/trac/wiki/UsrpFAQ/Latency

Is there similar calculations about the latency of the USRP2?

If there is not, could someone please do those calculations?

  • Pauli Rikula

#2

Hi,

If USRP2 can respond to PING and reply back, then one should be able to
measure the delay.

Regards,

Firas


#3

Hi,

Wouldn’t one be able to use for instance “set_freq()” or find() as a
messure? Although there might be some overhead, you will receive an “ok
I have set the freq”/“Ok here I am”- packet from the usrp2. Although one
could think of more elaborate schemes involving a special OP_CODE
(usrp2_eth_packet.h)…

Cheers
//Mattias K.


#4

On Wed, Nov 05, 2008 at 01:01:14PM +0200, Pauli Rikula wrote:

I foud this wery usefull: http://www.gnuradio.org/trac/wiki/UsrpFAQ/Latency

Is there similar calculations about the latency of the USRP2?

If there is not, could someone please do those calculations?

  • Pauli Rikula

I did some preliminary measurements a while ago. A round trip from
the host to the USRP2 and back was taking about 47us. It mostly
depends on how much data you’ve queued for transmission on the
ethernet. YMMV.

Eric


#5

set_freq would not be a good measure, since it takes a while to
configure the daughterboard. find() isn’t great either, since it
waits 10ms to ensure that it’s gathered all responses to it’s
broadcast.

set_rx_decim should give a reasonable measurement, as long as you’re
not streaming data.

BTW, I also have code which can be run which actually measures the
latency on USRP1, rather than just theoretical calculations that you’ve
found on the wiki:
https://www.cgran.org/wiki/ArchitectureLatencyMeasurements

It uses pings and some modifications to the Linux kernel to measure
latency from host->kernel->USRP, etc.

  • George

#6

On Wed, Nov 05, 2008 at 04:26:04PM +0100, Mattias K. wrote:

set_freq would not be a good measure, since it takes a while to
configure the daughterboard. find() isn’t great either, since it
waits 10ms to ensure that it’s gathered all responses to it’s
broadcast.

set_rx_decim should give a reasonable measurement, as long as you’re
not streaming data.

Eric