[mythtv-users] fine tuning on Plextor ConvertX

Nathan Lutchansky lutchann-mythtvusers at litech.org
Fri Feb 17 04:42:38 UTC 2006

On Thu, Feb 16, 2006 at 11:14:40PM -0500, Dale E. Martin wrote:
> > I don't know if the Plextor has provision to change the tuning table to
> > accomodate non-broadcast channel frequencies, I know some devices just
> > relay on very wide AFC windows to deal with it.
> The driver looked to me like it takes tuning requests in terms of frequency
> specified as an integer in kilohertz.

The V4L2 API works with frequencies in increments of 62.5 kHz, and the
Sony tuner inside the Plextor supports tuning in this step size.  In
fact, it will do 31.25 kHz increments as well, although this isn't
supported in V4L2.

> Of course, I don't know if the hardware downstream of the ioctl is
> doing something 'clever' with the request either - the driver loads a
> binary blob into the hardware.  (And it's not like I have schematics
> or data sheets anyways ;-))

The tuner control works through the standard Linux I2C API, so it's all
completely transparent to anybody who looks at the code.  Geez, don't be
givin' me trouble over those firmware blobs for no reason...

Anyway, if you can specify fine-tuning in Myth, it should certainly work
with the TV402U.  I wouldn't be surprised, though, if the settings that
worked with the BTTV card didn't work with the Plextor, as every tuner
has different tolerances on tuning slightly offset carriers.  -Nathan
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