On 06/14/2018 09:12 PM, Walter Maguire via USRP-users wrote:
Hi all,
I have a few questions concerning the connectivity capability of the
RFNoC system w.r.t the FPGA and the UHD driver.
The first of these concerns the limit of 16 CE blocks on the bus.
In an early RFNoC presentation it was suggested that a bridging CE
block could be designed to add another RFNoC network to the first
RFNoC network in a sort of daisy chain mode . Do Ettus have any
examples available which do this? Does the current UHD driver
handle CE discovery or enumeration over nested RFNoC buses? My
understanding is that whilst possible at a FPGA level it probably is
not very practical and is not supported by the current UHD driver.
Moving on from the situation described above, we could potentially
spread our RFNoC blocks over several USRP3 type devices using the SFP
10GSPs links to transfer between them. For example have one USRP3
device do the high speed front end processing and then pass the
results via SFP to a second USRP device to do complex algorithms of
the received data at a lower rate. How does the UHD driver and
GNURadio handle this scenario? Do we have to have 2 versions of
GNURadio running or does the UHD and GNURadio support seamless
connectivity of the entire system, assuming all blocks are
communicating using RFNoC packets?. Assuming the SFP connecting blocks
are RFNoC bridge how does the system handle multiple RFNoC connections
spread over multiple devices?
Another network type application might be looking at the same signal
received in different locations where the USRP3 radios are connected
by network to the one other USRP3 or PCs. How would this application
be accommodated for using the current UHD and GNURadio systems?
Regards
Walter
Certainly the scenario where one or more PCs are connected to one or
more USRPs can be made to work with existing tooling.
The simplest scenario is the well-supported "multi-usrp" on a single
host PC with one or more USRP devices connected. Various larger-scale
MIMO demos use this all the time from what I understand.
Once you move beyond a single PC, and view your collection of USRPs and
PCs as a kind of "radio processing fabric", then, no, UHD itself has
no inherent support for this, but one could probably put together a
working application scenario ON TOP, using UHD underneath.
Similarly, there's no inherent support for view a collection of
USRPs-with-RFNoC as a kind of "radio processing fabric", although one
could probably
make this work with a lot of custom "stuff" with existing hardware
and FPGA infrastructure. There's no existing "just use this API" that
enables
this mode of operations. I rather suspect that if you want more than
one FPGA to be working on a given radio stream, it may not make
economic sense to drag an entire USRP (X or N) into it, just for the
FPGA resources--you're dragging a lot of other hardware along
"for the ride".
I'm sure that Martin and others also have opinions on this. This was
just my first reaction...
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