Re: Writing Drivers for Custom Hardware

On 12/07/2024 16:42, Walter Szeliga 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
Are these things actually in production?  What kind of price range, and
how tunable in terms of center frequency are they?