18 May
2012
18 May
'12
3:22 a.m.
So I have been trying figure out why I have been having problems with NID decoding in
later versions of ubuntu, and have tracked it down to a difference in the versions of
libitpp and libitpp-dev. After installing the versions from the 11.04 package repository
(4.0.7-1, as opposed to 4.2-4 in 11.10 and onwards), it started working. The offending
function call appears to be on line 177 in op25_decoder_bf.cc, which is a call to
itpp::BCH.encode. It would be good if someone else could give this a try just to verify
that it is an issue with later versions of libitpp (even though the bch source code
doesn't appear to have changed in over 2 years...). Hope this info is of use to
someone.
Thanks,
Mark
--- In op25-dev(a)yahoogroups.com, "Matt" <matt.robert80@...> wrote:
One thing I need to clarify - when I say type 2 is a 3600 baud 2FSK system, I am
referring to the control channel only. The voice channels are, of course, C4FM.
The really strange thing is that I have been over the DSD source code, and it decodes
voice by specifically looking for LDU1 and LDU2 frames. If OP25 is detecting HDU frames,
then DSD should be also..
Cheers,
Matt
--- In op25-dev(a)yahoogroups.com, "rrgsti" <bobrich@> wrote:
Interesting! I did see on the MARCS page at Ohio.gov say that they were planning to
upgrade to P25, which was a bit confusing.
These are the control channels I'm able to see in UniTrunker with my little home-brew
antenna. These are all around central/western ohio. The first one is the only analog
system, and the signal is pretty poor.
http://i.imgur.com/CoNGl.png
I am able to decode the voice channels a bit in DSD on Windows as well. It's
somewhat odd, as the voice, when it's smoothly decoded, is very high quality, but it
drops out quite a bit. I'm doing it through the audio output of HDSDR, though, which
is probably where the issue is.
Anyway, DSD does kick out some diagnostic info as well if that's of any use. I can
also get snapshots from Wireshark of the P25 CAI.
I do appreciate any effort put into this but please enjoy your weekend first and
foremost. :)
Take care.
--- In op25-dev(a)yahoogroups.com, "Matt" <matt.robert80@> wrote:
Aha - the plot thickens. Ohio MARCS isn't a true P25 system - its an old Type 2, 3600
baud 2FSK Motorola trunk system that has Motorola ASTRO CAI compatible voice channels.
These systems were implemented between 1996 and 2002 which is after Motorola ditched
VSELP as their codec and went to the CAI IMBE format that was ratified in 2002 as the real
P25 standard. These systems supported analog voice also, however MARCS has dropped that
and is only using digital voice.
These ASTRO voice channels use the same IMBE vocoder as a true P25 system, and a very
similar CAI compatible format, but the usual P25 fields are used for other purposes. The
NSWGRN used to use this before it went pure P25.
OP25 has been implemented to the P25 specs, which differ slightly form these systems.
The NAC values are calculated on these systems by a combination of the Type 2 System ID,
and the Analog connect tone code. Anyone who played with the old classic trunker on 3600
baud systems will recall this.
If you could list which site you are listening to and the system ID, I can look into it
further from some old notes that I have lying around.
--- In op25-dev(a)yahoogroups.com, "rrgsti" <bobrich@> wrote:
The capture is from a local repeater in the Ohio MARCS system. I get pretty strong
signals from a few of them, I believe this one in particular was from London, Ohio in
Madison county (the control channel may actually be in there as well). I do know that
RadioReference streams this repeater through a Uniden BC796D digital scanner.
I'd be happy to capture more if it's of any use or upload the files to another
location.
Thanks
--- In op25-dev(a)yahoogroups.com, Matt Robert <matt.robert80@> wrote:
>
> I thought the same thing but then recalled that 000 is not available as a NAC - the
standard defines the value as having the range 0x001-0xFFF.
>
> I think a capture file would be ideal - this is a curly one for sure!
>
> Bob - which system is this coming off?
>
> Cheers,
> Matt
>
>
> ________________________________
> From: Steve Glass <stevie.glass@>
> To: op25-dev(a)yahoogroups.com
> Sent: Thursday, 3 May 2012 11:31 AM
> Subject: Re: [op25-dev] Re: OP25 GRC - Almost but not quite working
>
>
> Â
> The 64 bit NID consists of the NAC+DUID (the low order 16 bits) and the error
correction bits (the high order 48 bits). Its possible the NAC is zero for a data frame
since it has its own addressing information within the frame itself. That would leave you
with just the DUID and the appropriate BCH code for that value. Its possible (but not very
likely) that this would mean the high order bits would be mostly zeroes.
>
>
> On 3 May 2012 01:02, rrgsti <bobrich@> wrote:
>
>
> >Â
> >Hi folks,
> >
> >I'm still tinkering with this but am running into a bit of a wall with
regards to P25 data.
> >
> >These two lines are dumped to stderr using a call to the dump_cw function that I
added to the code. I'm only dumping the first 30 bytes for brevity:
> >
> >
> >55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe
fc 25 ed
> >
> >55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 5b 10 ba 16 de 2e 82 69 36 3d 98 1f 9b
f8 8e c6
> >
> >
> Based on what I've been able to determine so far, the first 48 bits are frame
sync, and they should be fixed at 0x5575f5ff77ff, which is what we see above.
> >
> >The next 64 bits are supposed to be NID, which includes the DUID.
> >
> >I could be wrong, but I believe the 02 (which alternates between 02 and 03 in
the lines below) at the 9th byte, is the status bit-pair that is interleaved every 70
bits (9 bytes * 8 bits - 72 bits into the frame). Once removed, that shifts the remaining
bits to the left 2, which still leaves the NID essentially filled with zeroes except for
the last two bits. Immediately after the NID, however, the bits start flying again.
> >
> >Does this seem normal? I can't really find any annotated hex dumps of a P25
frame to try to line things up, but it seems that the NID should be populated with
something other than zeroes. If you bit shift the 15th bit 2 to the left, we'll get
a parity bit set every now and then (again, unless I'm messing something up), but
nothing else.
> >
> >I'm completely open to the fact that this could just be a bad signal, but I
can get very clear decodes of the voice if I force the type to LDU1 or LDU2, and I have
never seen anything but all zeroes here (across many minutes of decoded voice data)
> >
> >Any thoughts?
> >
> >
> >--- In op25-dev(a)yahoogroups.com, "rrgsti" <bobrich@> wrote:
> >>
> >>
> >> Hi Matt!
> >>
> >> Thanks for the info, it sounds like that is a very possible option. Is
there a way to see the state of the fsk4 demodulator? I did try running with the updated
OP25.py that Balint put out on Saturday (uses _op25.fsk4 instead of the Radio Raush
module, and it doesn't seem to behave any differently.
> >>
> >> I did find dump_cw in op25_imbe_frame.h and used it to dump frames right
before their duid is read. I don't know if these will be meaningful, but I'll
paste them in here. Moments of silence have the clusters of 0xff's on the right,
while portions where there is audio has more random numbers.
> >>
> >> I did note that about 9 bytes into this dump there is a byte that keeps
flipping between 2 and 3. Is it possible this is where the DUID is (shifted a bit or two).
Each row starting with 0x55 0x75 is a new frame dumped, I only dump the first 32 bytes or
so of each one.
> >>
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff
ff fe fc 25 ed
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff
ff fe fc 25 ed
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff
ff fe fc 25 ed
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff
ff fe fc 25 ed
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 03 0f 68 4f ff ff ff ff
ff fe fc 25 ed
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff
ff fe fc 25 ed
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff
ff fe fc 25 ed
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 5b 10 ba 16 de 2e 82 69 36 3d 98
1f 9b f8 8e c6
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 74 35 56 de 42 7b ac 05 90 af 5a
0e 12 84 81 6b
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 52 0b 37 d6 c5 a6 11 79 56 f5 9b
1a 1e 22 8a 35
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 7e 2d f0 82 d0 4f f8 4d a2 61 34
94 52 a4 f8 ec
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 4e 46 60 ce 5d a8 8b 27 7f 62 78
ab c2 52 ee 0f
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 00 00 00 02 55 75 f5 ff 77 ff 2d
6f ae e2 78 2e
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff
ff fe fc 25 ed
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff
ff fe fc 25 ed
> >> 55 75 f5 ff 77 ff 00 00 03 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff
ff fe fc 25 ed
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff
ff fe fc 25 ed
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff
ff ff fc 25 ed
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 45 5e a4 8b 59 7f 74 31 29 f3 ed
d2 36 6c fa 30
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 46 33 55 22 52 69 8e 51 5c 01 0b
ae 5a eb 36 8f
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 5b 10 ba 16 de 2e 82 69 36 3d 98
1f 9a f8 8e c6
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 00 00 00 02 55 75 f5 ff 77 ff 2d
6f ae e2 78 2e
> >> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff
ff fe fc 25 ed
> >>
> >>
> >>
> >
> >> --- In op25-dev(a)yahoogroups.com, Matt Robert <matt.robert80@> wrote:
> >> >
> >> > Hi Bob,
> >> >
> >> > Its more than likely a result of a bad signal. The FSK4 demod tends to
output zeros when it loses sync which is why the DUID is erroneously coming up as 0x00.
> >> >
> >> > LDU1/2 are the two types of voice frames. LDU1 has signalling data
embedded and LDU2 has encryption sync data embedded.
> >> >
> >> > The kludge diff posted below will work - but only for valid frames
with a corrupt DUID value.
> >> >
> >> >
> >> > I'm sure the root cause is the FSK4 demod isn't locking
properly and causing a bad DUID value to be outputted. I have seen similar behaviour in
other areas of OP25 - for example I was looking at the IV/MI value (72 bits) on a local
P25 system here. Whenever the demodulator ran out of talent, it would output steams of
constant zeros.
> >> >
> >> > Ohio MARCS is a Type 2 Smartzone Omnilink System with CAI compatible
ASTRO voice channels - so its essentially P25 compatible. The P25 CAI spec was based on
the ASTRO CAI from the same era, so its essentially the same thing.
> >> >
> >> > Is the system running any form of simulcasting?ÃÂ
> >> >
> >> > Cheers,
> >> > Matt
> >> >
> >> > ________________________________
> >> > From: rrgsti <bobrich@>
> >
> >> > To: op25-dev(a)yahoogroups.com
> >> > Sent: Thursday, 26 April 2012 10:59 PM
> >> > Subject: [op25-dev] Re: OP25 GRC - Almost but not quite working
> >> >
> >> >
> >> > ÃÂ
> >> > Quick update from my end.
> >> >
> >> > It looks like every frame coming out of the fsk4 demodulator (I'm
assuming, still a n00b here) is marked with a 'duid' of 0x0. Consequently, when
data_unit.cc initializes a new data_unit from the frame, it is always creating it as an
HDU (P25 header) type. This then prevents the IMBE decoder from being executed b/c
it's not a voice data unit type (LDU1/LDU2 (no idea what these mean)).
> >> >
> >> > I figured maybe it has something to do with our system (Ohio MARCS)
not being full P25 compliant and not including metadata of any sort, so I just made the
following change to data_unit.cc and re-ran it:
> >> >
> >> > --- op25-orig/blocks/src/lib/data_unit.cc 2012-04-24
10:31:29.139694592 -0400
> >> > +++ op25/blocks/src/lib/data_unit.cc 2012-04-26 08:12:35.183962129
-0400
> >> > @@ -39,7 +39,8 @@
> >> > uint8_t duid = extract(frame_body, 60, 64);
> >> > switch(duid) {
> >> > case 0x0:
> >> > - d = data_unit_sptr(new hdu(frame_body));
> >> > + //d = data_unit_sptr(new hdu(frame_body));
> >> > + d = data_unit_sptr(new ldu1(frame_body));
> >> > break;
> >> > case 0x3:
> >> > d = data_unit_sptr(new tdu(frame_body, false));
> >> >
> >> > This seemed to sort of work as I now get rather garbled, but
intelligible, audio from the decoder.
> >> >
> >> > I've uploaded the baseband capture (1Msps) and resulting audio
.wav file that I get at the following URLS:
> >> >
> >> > http://s3.amazonaws.com/public-xrp/p25.iq.bz2
> >> > http://s3.amazonaws.com/public-xrp/p25.wav
> >> >
> >> > Not sure if this is of any use, but it is encouraging to hear voices
at least. :)
> >> >
> >> > Thanks!
> >> >
> >> > Bob
> >> >
> >> > --- In op25-dev(a)yahoogroups.com, Andy Knitt <andyknitt@> wrote:
> >> > >
> >> > > It looks like imbe_decoder_factory.cc in OP25 defaults to
> >> > > 'software_imbe_decoder'. I manually changed the IMBE
environment variable
> >> > > to "soft" and confirmed it with printenv, but I'm
still getting a flat line
> >> > > at the output of the OP25 block. Any other ideas?
> >> > >
> >> > > Thanks,
> >> > >
> >> > > Andy
> >> > >
> >> > > On Mon, Apr 23, 2012 at 11:47 PM, Balint <balint256@>
wrote:
> >> > >
> >> > > > **
> >> > > >
> >> > > >
> >> > > > I *still* haven't checked out the latest code, but in my
old code the
> >> > > > default voice frame output was (null?).****
> >> > > >
> >> > > > There are options for file output, null, external (hardware)
decoder and
> >> > > > internal decoder. You used to be able to spec this on the
command line as
> >> > > > an environment variable:****
> >> > > >
> >> > > > export IMBE=soft****
> >> > > >
> >> > > > I changed my default to be the internal decoder (see
> >> > > > `imbe_decoder_factory.cc').****
> >> > > >
> >> > > > ** **
> >> > > >
> >> > > > *From:* op25-dev(a)yahoogroups.com
[mailto:op25-dev@yahoogroups.com] *On
> >> > > > Behalf Of *Andy Knitt
> >> > > > *Sent:* Tuesday, 24 April 2012 12:45 PM
> >> > > > *To:* op25-dev(a)yahoogroups.com
> >> > > > *Subject:* [op25-dev] OP25 GRC - Almost but not quite
working****
> >> > > >
> >> > > > ** **
> >> > > >
> >> > > > ****
> >> > > >
> >> > > > I have the OP25 GRC demo that Balint provided up and
running.
> >> > > > Everything seems to working except I'm not getting any
audio out of
> >> > > > the OP25 block. I'm getting the "four line"
output from the dibit
> >> > > > output port when there is traffic on the channel, and the
autotune
> >> > > > output is outputting data. However, no audio. I put a scope
on the
> >> > > > audio output and it's a flat line at zero, even when the
dibit output
> >> > > > is "four lines". Any tips on how to further
troubleshoot?
> >> > > >
> >> > > > Thanks,
> >> > > >
> >> > > > Andy****
> >> > > >
> >> > > > ****
> >> > > >
> >> > > >
> >> > > >
> >> > >
> >> >
> >>
> >
> >
>