[mythtv-commits] Ticket #841: Approach to scanning 'other'
frequencies
MythTV
mythtv at cvs.mythtv.org
Tue Dec 20 06:22:48 EST 2005
#841: Approach to scanning 'other' frequencies
----------------------------------------+-----------------------------------
Reporter: mythdev at penyball.cix.co.uk | Owner: ijr
Type: enhancement | Status: new
Priority: minor | Milestone: 0.20
Component: mythtv | Version: head
Severity: low |
----------------------------------------+-----------------------------------
The current DVB-T scan ignores 'other frequencies' which means that it is
broken for some transmiters eg Moel Y Parc - which is a UK DVB-T
transmitter
This note is here as "low priority enhancement" because there is an easy
workaround - import channels.conf - I'm submitting this to summarise what
I have found to date - to help anyone who looks at this in the future.
MoelYParc maintains 6 transport streams reported in the NIT as below:
(all transports have the Other_Frequency flag set to 1,
the frequencies marked with ** are those which carry the signal
associated with the transport,
those marked with a single * also tune because they are carrying the
signal for "other" transports)
{{{
tsid: 4158 Centre Frequency 546000.000 (*)
Other Frequencies:
530166.067
746000.000
505833.033
722000.000
682166.067
** 738000.000
530166.067
706000.000
tsid: 8205 Centre Frequency 578000.000 (*)
Other Frequencies:
562166.067 kHz)
825833.033 kHz)
481833.033 kHz)
690000.000 kHz)
714166.067 kHz)
** 770000.000 kHz)
482166.067 kHz)
* 738166.067 kHz)
tsid: 12289 Centre Frequency 625833.033
Other Frequencies:
489833.033
777833.033
529833.033
642000.000
618000.000
** 794000.000
506166.067
* 770166.067
tsid: 16384 Centre Frequency 705833.033
Other Frequencies:
513833.033
801833.033
561833.033
666000.000
641833.033
** 818000.000
562166.067
* 794166.067
tsid: 20480 Centre Frequency 649833.03
Other Frequencies:
538166.067
850000.000
474000.000
482166.067
665833.033
** 546000.000
538166.067
* 818166.067
tsid: 24576 Centre Frequency 673833.033
Other Frequencies:
570166.067
834166.067
553833.033
530166.067
697833.033
** 578000.000
570166.067
674000.000
}}}
The issue with the current scan against this nit is that it does not look
at 'other frequencies' and inserts only the centre-frequencies into
dtv_multiplex
therefore in the case above the scan will only detect channels for tsid
4158 and 8205. (Which are actually the channels for tsid 20480 and 24576
respectively - but this doesn't matter because we never use the tsid as a
crosscheck) An additional consequence is that the transports stored in
dtv_multiplex are invalid in that either the frequency doesn't tune or -
in all cases the transportid is associated with the wrong frequency.
My reading of the DVB-T specifications suggest that it is not clear
whether or not:
a) The centre frequency may carry a signal when the 'other_frequency' flag
is set
b) A single transport may be carried on multiple frequencies from a single
transmitter.
or c) There is any standardised or dependent 'ordering' of
transports/frequencies in the NIT
The sample code in the checknit attached assumes that:
If the other_frequency is set - the centre frequency is not in use for
that transport.
A single transport may be carried on multiple frequencies from the same
transmitter - so all 'other' frequencies need to be scanned if the
'other_frequency' flag is set.
The sample code checks the 'other frequencies as follows:
Tune to each frequency.
if SYNC bytes are detected then save the frequency, the tsid and signal
strength as 'valid'
When the scan is complete:
Sort the saved frequency list in ascending order of frequency and
transportid
- the nit above produces the following 'valid frequency' list:
{{{
546000.000 20480
578000.000 24576
738000.000 4158
X 738166.067 8205
770000.000 8205
X 770166.067 12289
794000.000 12289
X 794166.067 16384
818000.000 16384
X 818166.067 20480
}}}
Then scan through this list, in order, removing any frequency that is
within 2 offsets of the previous frequency. - this removes all those above
marked with an X.
(At the moment the code doesn't use the signal strength but at some point
the strongest signal for a given transport id may need to be chosen?)
This works for the moelyparc transmitter and accidentally? gets the
transport id associated with the right frequency. However the approach as
coded looks unsatisfactory - eg if 8205 had 793834.000 as a possible
'other frequency' then the 12289 transport would be 'lost'.
I think that what is needed is to ensure that all valid frequencies are
captured (those within 2 offsets being equivalent) and to ensure that
these have a 'unique' transportid as a key into the multiplex table. Its
not clear to me at the moment what sort of convoluted parsing of this list
would be necessary to ensure that is true!
The first patch below should be 'safe' it simply decodes the
other_frequency flag.
The second patch implements the approach above - it modifies the commented
out parts of the existing CheckNIT and provides a 'tuneTransport' function
in DVBChannel. The updates to 'wait_for_backend' work on bt878 and
ttusb_dec but the comments already in here look like this is a minefield
:)
other_frequency patch:
{{{
Index: mythtv/libs/libmythtv/siparser.cpp
===================================================================
--- mythtv/libs/libmythtv/siparser.cpp (revision 8325)
+++ mythtv/libs/libmythtv/siparser.cpp (working copy)
@@ -1743,6 +1743,10 @@
default:
retval.TransmissionMode = "auto";
}
+
+ //Other_frequency - true if additional frequency is in use
+ retval.Other_frequency = (( buffer[8] & 0x01 ) == 1);
+
return retval;
}
Index: mythtv/libs/libmythtv/sitypes.h
===================================================================
--- mythtv/libs/libmythtv/sitypes.h (revision 8325)
+++ mythtv/libs/libmythtv/sitypes.h (working copy)
@@ -419,6 +419,8 @@
QString GuardInterval;
QString TransmissionMode;
QString Inversion;
+ // other_frequency true if one or more of additional frequencies is
in use
+ bool Other_frequency;
//Additional frequencies
QValueList<unsigned> frequencies;
Index: mythtv/libs/libmythtv/sitypes.cpp
===================================================================
--- mythtv/libs/libmythtv/sitypes.cpp (revision 8325)
+++ mythtv/libs/libmythtv/sitypes.cpp (working copy)
@@ -344,6 +344,7 @@
GuardInterval = "auto";
TransmissionMode = "a";
Inversion = "a";
+ Other_frequency = false;
}
void NetworkObject::Reset()
}}}
CheckNIT patch:
{{{
Index: mythtv/libs/libmythtv/dvbchannel.h
===================================================================
--- mythtv/libs/libmythtv/dvbchannel.h (revision 8325)
+++ mythtv/libs/libmythtv/dvbchannel.h (working copy)
@@ -65,6 +65,7 @@
bool SwitchToInput(const QString &inputname, const QString &chan);
bool SwitchToInput(int newcapchannel, bool setstarting);
bool Tune(const dvb_channel_t& channel, bool force_reset=false);
+ uint TuneTransport(const DVBTuning& tuning, uint signalTimeout=5);
// Set/Get/Command just for SIScan/ScanWizardScanner
void SetMultiplexID(int mplexid) { currentTID = mplexid; };
Index: mythtv/libs/libmythtv/dvbchannel.cpp
===================================================================
--- mythtv/libs/libmythtv/dvbchannel.cpp (revision 8325)
+++ mythtv/libs/libmythtv/dvbchannel.cpp (working copy)
@@ -686,6 +686,59 @@
return true;
}
+/** \fn DVBChannel::TuneTransport(const DVBTuning&, uint)
+ * \brief Tunes the card to a frequency but does not deal with PIDs.
+ *
+ * \param tuning Transport to tune to
+ * \param signalTimeout Maximum time to wait for FE_HAS_SYNC
+ * \return signal strength on success, 0 on failure
+ */
+uint DVBChannel::TuneTransport(const DVBTuning& tuning, uint
signalTimeout)
+{
+ bool has_diseq = (FE_QPSK == info.type) && diseqc;
+ struct dvb_frontend_parameters params = tuning.params;
+
+ if (fd_frontend < 0)
+ {
+ ERROR("DVBChannel::TuneTransport: Card not open!");
+ return 0;
+ }
+
+ // Remove any events in queue before tuning.
+ drain_dvb_events(fd_frontend);
+
+ // Send DisEq commands to external hardware if we need to.
+ if (has_diseq && !handle_diseq(tuning, diseqc, true))
+ {
+ ERROR("DVBChannel::TuneTransport: Failed to transmit DisEq
commands");
+ return 0;
+ }
+
+ CHANNEL("TTOld Params: "<<toString(prev_tuning.params, info.type));
+ CHANNEL("TTNew Params: "<<toString(tuning.params, info.type));
+
+ // Adjust for Satelite recievers which offset the frequency.
+ params.frequency = tuned_frequency(tuning, info.type, NULL);
+
+ if (ioctl(fd_frontend, FE_SET_FRONTEND, ¶ms) < 0)
+ {
+ ERRNO("DVBChannel::TuneTransport: "
+ "Setting Frontend tuning parameters failed.");
+ return 0;
+ }
+ if ( !wait_for_backend( fd_frontend, signalTimeout) )
+ return 0;
+
+ prev_tuning.params = params;
+ CHANNEL("DVBChannel::TuneTransport: Frequency has signal.");
+
+ uint16_t sig = 0;
+ if (ioctl(fd_frontend, FE_READ_SIGNAL_STRENGTH, &sig) < 0 )
+ return 100;
+ else
+ return sig;
+}
+
/** \fn DVBChannel::GetTuningParams(DVBTuning& tuning) const
* \brief Fetches DVBTuning params from driver
* \return true on success, false on failure
@@ -815,15 +868,34 @@
*/
static bool wait_for_backend(int fd, int timeout_ms)
{
- struct timeval select_timeout = { 0, (timeout_ms % 1000) * 1000
/*usec*/};
- fd_set fd_select_set;
- FD_ZERO( &fd_select_set);
- FD_SET (fd, &fd_select_set);
+ struct timeval select_timeout;
+ struct dvb_frontend_event event;
+ bzero(&event, sizeof(struct dvb_frontend_event));
- // Try to wait for some output like an event, unfortunately
- // this fails on several DVB cards, so we have a timeout.
- select(fd+1, &fd_select_set, NULL, NULL, &select_timeout);
+ MythTimer t;
+ t.start();
+ while (((event.status & FE_TIMEDOUT)==0) &&
+ ((event.status & FE_HAS_SYNC)==0) && (t.elapsed()<
timeout_ms))
+ {
+ select_timeout.tv_sec = 0; select_timeout.tv_usec = 10000;
+ fd_set fd_select_set;
+ FD_ZERO( &fd_select_set);
+ FD_SET (fd, &fd_select_set);
+
+ // Try to wait for some output like an event, unfortunately
+ // this fails on several DVB cards, so we have a timeout.
+ if (select(fd+1, &fd_select_set, NULL, NULL, &select_timeout) >
0)
+ {
+ bzero(&event, sizeof(struct dvb_frontend_event));
+ if (ioctl(fd, FE_GET_EVENT, &event) < 0)
+ {
+ if (errno != EOVERFLOW)
+ return false;
+ }
+ }
+ }
+
// This is supposed to work on all cards, post 2.6.12...
fe_status_t status;
if (ioctl(fd, FE_READ_STATUS, &status) < 0)
@@ -833,10 +905,13 @@
.arg(strerror(errno)));
return false;
}
-
VERBOSE(VB_CHANNEL, QString("dvbchannel.cpp:wait_for_backend: Status:
%1")
.arg(toString(status)));
- return true;
+
+ if ( status & FE_HAS_SYNC )
+ return true;
+ else
+ return false;
}
/** \fn handle_diseq(const DVBTuning&, DVBDiSEqC*, bool)
Index: mythtv/libs/libmythtv/siscan.cpp
===================================================================
--- mythtv/libs/libmythtv/siscan.cpp (revision 8325)
+++ mythtv/libs/libmythtv/siscan.cpp (working copy)
@@ -707,9 +707,6 @@
return ok;
}
-#undef SIP_RESET
-#undef SIP_PMAP
-
void SIScan::ScanTransport(const transport_scan_items_it_t transport)
{
QString offset_str = (transport.offset()) ?
@@ -1554,10 +1551,43 @@
#endif // USE_SIPARSER
#ifdef USE_SIPARSER
+/** \fn SIScan::CheckNIT(NITObject& NIT)
+ *
+ * Check 'other' frequencies in the NIT transports. The
transport.frequency
+ * may not be valid - ie one or more of the transport.frequencies may be
used
+ * by the network so
+ *
+ * If the other_frequency flag is set this check should
+ * a) Tune to each frequency in the frequencies table
+ * b) If the tuning works - check the transportid of packets received
+ * if these match - the frequency is valid for the transport
+ * (The frequency could have tuned because it is valid for a
different transport)
+ *
+ * However its not easy to check the transportid in any packets received
in this part
+ * of the code - therefore we just use the first one identified in the
transport
+ *
+ */
+class TsFrequency
+{
+public:
+ TsFrequency() : fr(0),tsid(0) {}
+ TsFrequency( unsigned transportid, unsigned frequency, uint
signalStrength )
+ : fr(frequency),tsid(transportid),sstr(signalStrength) {}
+ virtual ~TsFrequency() {}
+ unsigned fr; // Frequency
+ unsigned tsid; // Transport stream ID
+ uint sstr; // Signal Strength
+ bool operator <( const TsFrequency& f1)
+ { return ( ( fr < f1.fr ) ||
+ ((fr == f1.fr) && (tsid < f1.tsid)) ); }
+};
+
void SIScan::CheckNIT(NITObject& NIT)
{
(void) NIT;
dvb_channel_t chan_opts;
+ QValueList<TsFrequency> validFrequencies;
+
QValueList<TransportObject>::Iterator t;
for (t = NIT.Transport.begin() ; t != NIT.Transport.end() ; ++t )
{
@@ -1602,30 +1632,61 @@
else //Lets hope we never get here
break;
-#if 0 // disable for now
- //Start off with the main frequency,
- if (GetDVBChannel()->TuneTransport(chan_opts, true,
channelTimeout))
- {
-// cerr << "Tuned to main frequency "<< transport.Frequency
<< "\n";
- continue;
- }
+ // If the 'other frequency in use' flag is set then tune to each
+ // otherwise just check the main frequency
+ //
+ uint sstr = 0;
+ DVBChannel *dvbc = GetDVBChannel();
+ if ( !transport.Other_frequency )
+ {
+ SIP_RESET();
+ sstr = dvbc->TuneTransport(chan_opts.tuning, signalTimeout);
+ if ( sstr > 0 )
+
validFrequencies.append(TsFrequency(transport.TransportID,transport.Frequency,sstr));
+ }
+ else // other_frequency is in use
+ {
+ emit TransportScanUpdateText(QString(
+ "Checking alternative Frequencies for Transport: %1")
+ .arg(transport.TransportID));
- //Now the other ones in the list
- QValueList<unsigned>::Iterator f;
- for
(f=transport.frequencies.begin();f!=transport.frequencies.end();f++)
- {
- unsigned nfrequency = *f;
- chan_opts.tuning.params.frequency = nfrequency;
-// cerr << "CheckNIT " << nfrequency << "\n";
- if (GetDVBChannel()->TuneTransport(chan_opts, true,
channelTimeout))
+ QValueList<unsigned>::Iterator f;
+ for
(f=transport.frequencies.begin();f!=transport.frequencies.end();f++)
{
-// cerr << "Tuned frequency "<< nfrequency << "\n";
- transport.Frequency = nfrequency;
- break;
+ unsigned nfrequency = *f;
+ chan_opts.tuning.params.frequency = nfrequency;
+ SIP_RESET();
+ sstr = dvbc->TuneTransport(chan_opts.tuning,
signalTimeout);
+ if ( sstr > 0 )
+
validFrequencies.append(TsFrequency(transport.TransportID,nfrequency,sstr));
}
}
-#endif
}
+ // sort the valid frequencies in order of frequency, transportid
+ qHeapSort(validFrequencies);
+ // Run through the valid list removing frequencies within 33400Hz of
the previous frequency
+ unsigned lastFrequency = 0;
+ QValueListIterator<TsFrequency> it;
+ for ( it = validFrequencies.begin(); it != validFrequencies.end(); )
+ {
+ if (((*it).fr - lastFrequency ) < 334000 )
+ it = validFrequencies.remove(it);
+ else
+ { lastFrequency = (*it).fr; ++it; }
+
+ }
+
+ // finally update the transports with the first valid frequency
+ // if signal strength was being reported we could pick the
strongest here
+ for (t = NIT.Transport.begin() ; t != NIT.Transport.end() ; ++t )
+ {
+ for ( it = validFrequencies.begin(); it !=
validFrequencies.end(); ++it )
+ {
+ if ( (*t).TransportID == (*it).tsid )
+ { (*t).Frequency = (*it).fr; break; }
+ }
+ }
+
}
#endif // USE_SIPARSER
}}}
--
Ticket URL: <http://cvs.mythtv.org/trac/ticket/841>
MythTV <http://www.mythtv.org/>
MythTV
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