[linux-dvb] Re: DVB-T and zigzag scans question

[Holger Waechtler <holger@convergence.de>]

Andrew de Quincey wrote:
> With DVB-T, the zigzag scanning code chooses a step size as follows:
>
> stepsize = fe->info->frequency_stepsize * 2;
>
> frequency_stepsize for OFDM frontends seems to be set to 166667 usually, which 
> means it zigzags using a stepsize of 333334.
>
> Thing is, in my experience, frequency bending doesn't work for DVB-T either. 
> Using a stepsize of 166667 for trying to lock on to a slightly displaced 
> signal is way too large, let alone 333334.
>
> My guess for the problems with the tda100045h is that it loses the lock, kicks 
> off a zigzag scan, then never manages to tune again because the steps are so 
> large.
>
> Does zigzag scanning/frequency bending work for anyone with DVB-T cards? Or is 
> it some quirk here in the UK that means it achieves nothing useful?
>
> I notice for DVB-C cards, zigzag scanning is disabled: stepsize is hardcoded 
> to 0. 
Just add FE_CAN_RECOVER to the capabilities flags if your frontend does 
not needs to zigzag...

Holger



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