[linux-dvb] Re: Tuning problems with the refactored drivers

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

On Monday 18 Oct 2004 21:29, lamikr wrote:
> Andrew de Quincey wrote:
> >>First it tuned pretty badly. (Only 30 channels or so found) but after
> >>that I added the mdelay(200)
> >>command to line 116 of ves1820.c method ves1820_setup_reg0 and it
> >>started to tune channels very well.
> >>Now it can even find channels from out national tv channel! So maybe the
> >>mdelay-line should also be added in the
> >>CVS? (mdelay(50) got removed when you removed that hack)
> >>
> >>    ves1820_writereg(state, 0x00, reg0 & 0xfe);
> >>    ves1820_writereg(state, 0x00, reg0 | 0x01);
> >>    mdelay(200);                                                      //
> >>this is the new line!
> >
> >Does setting the dvb_override_tune_delay parameter to 200 have the same
> > effect as doing this? Its just that there is a mechanism defined for
> > solving exactly this problem which I would prefer to use rather than
> > putting an mdelay in the frontend itself.
> >
> >Glad to hear its getting better!
>
> How can I test this? Should I change in /build-2.6/insmod.sh
>
>     insmod ./ves1820.ko
> to
>     insmod ./ves1820.ko dvb_override_tune_delay=200
> ?

insmod ./dvb-core.ko dvb_override_tune_delay=200

> >>Is this ms line btw. CPU speed dependent. (Would slow PC's require
> >>longer delay and faster one shorter?)
> >
> >It shouldn't do - the demod has its own clock.
>
> I am just trying to understand a little bit bigger picture where this is
> delay is actually affecting on.
> Will this delay somehow cause tune function from usermode to block a
> little bit longer so that the demod hardware
> has a little bit more time to really find channels from the stream?

Pretty much - currently the tuning is done by a kernel thread. It tries 
different combinations of parameters successively until it gets a lock - the 
delay just causes it to wait longer between tries.

> Btw. even I can now tune all channels ok, I have still problems to get
> some of the channels locked. (these from the 162 mhz)
> (Some others locks very fastly)
>
> [lamikr@aragorn szap]$ ./czap "YLE TV1"
> using '/dev/dvb/adapter0/frontend0' and '/dev/dvb/adapter0/demux0'
> reading channels from file '/home/lamikr/.czap/channels.conf'
>  19 YLE TV1:162000000:INVERSION_AUTO:6900000:FEC_NONE:QAM_128:512:650:17
>  19 YLE TV1: f 162000000, s 6900000, i 2, fec 0, qam 4, v 0x200, a 0x28a

Does that channel have a low symbol rate? With DVB-S cards (STV0299B based) 
I've had problems locking on with such channels (say < 10000000) - can take a 
number of seconds to get a lock.