On Wednesday 18 January 2012 14:40:09 Mauro Carvalho Chehab wrote:
> Em 18-01-2012 10:49, Patrick Boettcher escreveu:
> > On Tuesday 17 January 2012 19:45:28 you wrote:
> >> On ISDB-T, a few carriers are reserved for TMCC decoding
> >> (1 to 20 carriers, depending on the mode). Those carriers
> >> use the DBPSK modulation, and contain the information about
> >> each of the three layers of carriers (modulation, partial
> >> reception, inner code, interleaving, and number of segments).
> >>
> >> If the TMCC carrier was not locked and decoded, no information
> >> would be provided by get_frontend(). So, instead of returning
> >> false values, return -EAGAIN.
> >>
> >> Another alternative for this patch would be to add a flag to
> >> fe_status (FE_HAS_GET_FRONTEND?), to indicate that the ISDB-T
> >> TMCC carriers (and DVB-T TPS?), required for get_frontend
> >> to work, are locked.
> >>
> >> Comments?
> >
> > I think it changes the behaviour of get_frontend too much and in
> > fact transmission parameter signaling (TPS for DVB-T, TMCC for
> > ISDB-T) locks are already or should be if not integrated to the
> > status locks.
> >
> > Also those parameters can change over time and signal a
> > "reconfiguration" of the transmission.
> >
> > So, for me I would vote against this kind of implementation in
> > favor a better one. Unfortunately I don't have a much better idea
> > at hand right now.
>
> The current status are:
>
> typedef enum fe_status {
> FE_HAS_SIGNAL = 0x01, /* found something above the noise
> level */ FE_HAS_CARRIER = 0x02, /* found a DVB signal */
> FE_HAS_VITERBI = 0x04, /* FEC is stable */
> FE_HAS_SYNC = 0x08, /* found sync bytes */
> FE_HAS_LOCK = 0x10, /* everything's working... */
> FE_TIMEDOUT = 0x20, /* no lock within the last ~2
> seconds */ FE_REINIT = 0x40 /* frontend was reinitialized, */ }
> fe_status_t; /* application is recommended to
> reset */
>
> There are a few options that can be done:
>
> 1) only rise FE_HAS_LOCK if TPS/TMCC demod were locked. The
> "description" for FE_HAS_LOCK ("everything's working") seems to
> indicate that TMCC lock/TPS lock is also part of "everything".
HAS_LOCK includes TPS-lock, right. But TPS-lock can raise much before
HAS_LOCK and at worse signal conditions. In DVB-T and ISDB-T we can have
the parameters at -1 dB SNR (or below) whereas data reception at least
needs ~3 dB ( QPSK 1/2 in DVB-T) and much more for the modulations
used currently on earth.
> 2) create a new status for it.
Maybe that's the way to go then. FE_HAS_PARAMETERS.
> With regards to dvb-core get_frontend() call, it only makes sense if
> the TPS/TMCC is locked. So, I think that such call needs to be
> limited to happen only when the lock were archived, like the
> enclosed patch.
OK.
--
Patrick Boettcher
Kernel Labs Inc.
http://www.kernellabs.com/
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