On Fri, 2014-04-25 at 17:22 -0400, Andy Walls wrote: [snip] > > On Fri, Apr 25, 2014 at 2:14 PM, Andy Walls > > <a...@silverblocksystems.net> wrote: > > Hi. > > > > What is the recommended gr-ais repo/branch/commit that yields > > a working > > gr-ais with GnuRadio 3.7.x (git commit > > 3831dd37c8df19e25fa258db4d393ee068889dae) > > and the Ettus UHD 3.7.1 > > > > GitHub shows this fork network: > > https://github.com/bistromath/gr-ais/network > > > > Right now I'm using bistromath/gr-ais commit > > 754c13ca4f1c3fb0d079d3a42002b0dade2268ff > > (master HEAD, IIRC), but I'm not getting *any* !AIVDM output > > to the terminal window.
Well, I've identified one problem. The "unstuff" operation is being applied before the correlator for the start flag of 01111110 (0x7e). The start flag, end flag, and preamble are not subject to bit stuffing per ITU-R M.1371-4 Annex 2 Sections 3.2.2.1 through 3.2.2.4. I suspect this causes a problem with proper detection of the start of the message, as the unstuff, as I understand it, will change the start flag from 01111110 to 0111110m, where m is the first bit of the message payload. Putting the unstuff operation after the correlators doesn't fix everything though. All potential message decodes still fail the CRC check. Bypassing the CRC check and inspecting the output !AIVDMs with gpsdecode verifies they are junk. :( Regards, Andy _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
