On 12/07/2024 20:25, Chris Kuethe wrote:
I've not played with the ZMQ blocks, but a number of other drivers can
operate in network mode, eg. UHD, SoapySDR, and rtlsdr. Since the
firehose appears to use 2-bit samples I feel like you could fairly
easily convert that into something resembling rtl_tcp
(https://github.com/osmocom/rtl-sdr/blob/master/src/rtl_tcp.c#L95).
Linux supports "raw" sockets that don't have to be attached to any of
the TCP/IP mechanisms--that's how sniffers
like Wireshark, etc, work.
https://www.opensourceforu.com/2015/03/a-guide-to-using-raw-sockets/
I've done this in the very distant past (like, a couple of decades
ago). So writing a driver would involve understanding
the semantics of a "raw" socket, and understanding the architecture
of Gnu Radio "sources".
On Fri, Jul 12, 2024 at 3:55 PM Walter Szeliga
<walter.szel...@gmail.com> wrote:
Hi all,
I have a GNSS Firehose
(https://transitiva.com/product/gnss-firehose-receiver-tri-band-quad-constellation/)
and have been trying to get it working, in a streaming capacity,
with Gnuradio. The Firehose sends packets over ethernet using the
experimental ethertype 0x88b5. I've tried a few things to get data
from the Firehose into Gnuradio, some have worked, others have
not. Things that work:
* Use tcpdump and filter on 0x88b5 and save to a file. Open and
repackage each packet in the pcap dump as interleaved bytes of I&Q
and save to a file. Read into Gnuradio.
* Write a custom program using libpcap to filter on 0x88b5 on a
selected interface, repackage the packets and write directly to a
file. Read into Gnuradio.
* Write a custom program using libpcap to filter on 0x88b5 on a
selected interface, repackage the packets and PUB them using ZMQ.
SUB to this PUB using a simple Python script and dump the message
contents to a file. Read into Gnuradio. Both tcp and ipc PUB/SUB
work equally well.
Some things that do not work:
* SUB to the ZMQ PUB/SUB using the Gnuradio ZMQ SUB Source block.
* Write a custom program using libpcap to filter on 0x88b5 on a
selected interface, repackage the packets and send them using UDP.
The UDP approach doesn't work because too many packets get dropped
and I have been unable to set sysctl values appropriately (on an
M1 Mac) to avoid dropping too many packets.
I'm not sure why the ZMQ approach does not work with Gnuradio.
I've tried many simple flowgraphs to convert from vector to
stream, ibyte to complex, you name it, and then dumping the data
back out to a file using a File Sink (just to use existing
software to check for data sanity). Data gets into Gnuradio, but
it clearly loses something because constellation diagrams of the
output data become blobs centered on the origin rather than pairs
of point clouds offset from the origin as one would expect from
the BPSK nature of the GNSS signals captured by the Firehose.
I've come to the realization that it's probably best to write some
sort of driver to get data straight from the Firehose into
Gnuradio, but I have no idea where to start with this. Any ideas
about how to fix my ZMQ approach or start writing a custom driver
would be appreciated. There's a lot in here, so let me know if you
would like code or flowgraph examples.
Cheers,
Walter
--
GDB has a 'break' feature; why doesn't it have 'fix' too?
