[linux-dvb] qam256 problem with Technotrend C2300 DVB-C card

Andrew de Quincey adq_dvb at lidskialf.net
Sat Nov 18 14:14:19 CET 2006

On Saturday 18 November 2006 10:07, e9hack wrote:
> Andrew de Quincey wrote:
> > On Sunday 08 October 2006 08:43, e9hack wrote:
> >> Hi,
> >>
> >> I've problems with the TT-C2300 DVB-C card and qam256 modulated
> >> channels. After switching to a qam256 channel, the card needs between
> >> 0.5 and 1 hour to get the lock. Possible it is a problem of the reduced
> >> i2c bus speed. If the stv0297 is accessed with a higher i2c bus speed,
> >> the card gets the lock within a few seconds like qam64. I've attach a
> >> patch, which does reduce the i2c bus speed for the tuner only. I've
> >> measured the time between 'after tuning' and 'start waiting for the agc
> >> lock' in stv0297_set_frontend(). Without the patch it needs 470ms and
> >> with the patch 60ms. This is a little bit strange, because the factor of
> >> the speed changing is two. Possible, there is a bug in the spec of the
> >> saa7146.
> >
> > Looks sensible to me; no point slowing the demod access just for the
> > tuner. Will commit once you send me a signed off by line for it...
> The i2c-bus speed problem is already fixed by
> http://linuxtv.org/hg/v4l-dvb?cs=4a4213dbb9b8;style=gitweb. It was a
> problem of the max loop count in saa7146_i2c_writeout(). The saa7146 can
> transfer three bytes over the i2c-bus with one upload. The TT-C2300 uses
> a reduced i2c speed of 137.5kHz. This is necessary, because the pll chip
> (tda6405) has a max i2c-speed of 150kHz. The time for a transfer of
> three bytes is ca. 200us. With the old max loop count of 20, I got an
> additional delay of 1ms for the half of the transfers. This has
> increased the initialization time of the stv0297.
> I think. it isn't necessary to commit this patch.

Cool! Sorry - I was away for a bit and missed that. No need to commit as you 

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