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

[Johannes Stezenbach <js@convergence.de>]

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.

Johannes


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