[linux-dvb] Re: Another issue: frontend timeout value and low symbol rates

[Andrew de Quincey <adq_dvb@lidskialf.net>]

On Saturday 21 February 2004 17:16, Johannes Stezenbach wrote:
> Andrew de Quincey wrote:
> > Just noticed another problem.. I've never been able to lock on to low
> > symbol rate channels before... however, in diagnosing the other STV0299
> > problems, I disabled the FE_TIMEDOUT bit in dvb_frontend.c.
> >
> > Now, I'm able to lock on to low symbol rate signals... I've just managed
> > it with a 4340000 symbol rate... getting a REALLY good signal from it,
> > but it took about 10 seconds to tune (the current timeout is hardcoded to
> > 2 seconds). The STV0299B docs say it needs a certain number of symbols
> > before being able to get a lock... perhaps we need to have a timeout
> > which is based on the symbol rate. Again, I can just hack my userspace
> > app to ignore this bit, but IMO, it should be fixed in the driver.
> >
> > Opinions? If no one disagrees, I can sort something out....
>
> The ves1893 data sheet has some formlas for calculating the
> maximum sync time. Maybe some of them also apply to
> other demods. 10 sec could happen if you have too much noise and
> a worst case FEC, but I think the sync time depends only linearly
> on the symbol rate.

Thanks, I'll give them a look.

Hmm, I think I've tracked down one of the issues: stv0299_check_inversion(). 
This seems to not use the actual inversion value specifed in the frontend 
parameters... instead it just seems invert the inversion bit on every 
FE_SET_FRONTEND ioctl. This was causing my attempts to fail randomly. If I 
modify it to actually use the requested inversion, its getting more reliable 
(although not perfect yet).


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