I'm pretty sure the B200 defaults are:
send_frame_size = 8192
num_send_frames = 16
https://github.com/EttusResearch/uhd/blob/maint/host/lib/usrp/b200/b200_impl.cpp#L532
Ron
On 08/05/2017 12:00 AM, Dan CaJacob via USRP-users wrote:
Hi,
I have a GnuRadio modem I've developed and I'd like to reduce latency.
It does IP encapsulation and for testing, I use two USRPs to implement
an OTA connection between the modems.
I've reduced latency so far by 1) adding fill frames/bytes only at the
very last block before the USRP sink and 2) increasing the sample rate
to the device. This has gotten my slightly under 100 ms latency, which
is good compared to what I started with, but I think we can do better.
My assumption is that there is still some latency in the last buffer
between the last block and the USRP sink and perhaps some in the USRP
USB transport itself. I am using B200s in this case, BTW.
I suspect that what I really must do is now tweak the usrp buffer
params from here:
https://files.ettus.com/manual/page_transport.html But, I have no idea
what they are set to by default (any way to tell)? And some naive
manipulation of them hasn't improved anything.
I also tried tweaking the mx output buffer size on the last block
before the USRP sink without any improvement.
Any advice from Ettus folks would be appreciated :) I am giving a talk
at GRCon that addresses the latency reduction work so far, so if we
can get any more, I'll throw that in as well.
- Dan
--
Very Respectfully,
Dan CaJacob
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