Hello,
I am trying to make a simple FFT flow chart using a RFNoC FFT block
and a signal source as input. I am finding that the maximum FFT size I
can use is limited by the MTU of my Ethernet connection. While
connected to the 1GB Ethernet I had a MTU of 1500 and was able to use
an FFT size of 1024 but if I tried to use 2048 I would get a timeout
on chan0 error message, similar to this case
http://comments.gmane.org/gmane.comp.hardware.usrp.e100/13915 . I was
able to increase the FFT size to 1024 because I stayed in the RFNoc
layer to display data instead of moving back up to the host. If I move
up to the host layer then I am limited to FFT size of 512 like the
previous case.
I switched to a 10GB connection which supports a MTU of 9000. This
gave me a new max FFT size of 2048 if I stay in the RFNoC layer and
1024 if I move back up to the host layer. To do this I had to edit the
code for the RFNoC block like in this case
http://comments.gmane.org/gmane.comp.hardware.usrp.e100/16564. In that
example it is mentioned that it may be possible to break up larger
FFTs into multiple packets and recombine them.
I am wondering if there is a way to increase the FFT size past 2048
with a limited MTU. It aslo seems that the max packet size for the
USRP is 8000 so increasing the MTU further may be of little use.
FInally I am wondering if it is possible to have an FFT size up to
8192 and if not, will it be in the future?
I have attached my flowchart below