[linux-dvb] Writing DVB Software - couple questions

Johannes Stezenbach js at linuxtv.org
Wed Feb 23 00:41:14 CET 2005


On Wed, Feb 23, 2005 at 12:24:49AM +0100, Robert Schlabbach wrote:
> From: "Johannes Stezenbach" <js at linuxtv.org>
> > It's all undefined, as each demod hardware and driver has it's
> > own idea about them.
> 
> Which is not good. Each driver should be required to norm its signal
> statistics, e.g. to a percentage. Only the driver can "know" how to do
> this, and if the driver doesn't do it, the application can't do it either.
> 
> The Linux API should define exact value ranges for every statistic which
> every driver would be required to scale its hardware readings to. Then the
> statistics would actually be useful to applications for display purposes.

Yeah. Some values *are* scaled into 0..0xffff (e.g. snr), but that
still doesn't mean that you get well-defined values. E.g. some cards
will return 0x1234 and others 0x2345 for the same input signal. I don't
know how you want to calibrate this, even if you'd have a zoo of cards
to compare against each other I guess that for consumer equipment
even two "identical" cards will return different values...

Johannes




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