[linux-dvb] fmd1216 integration

Trent Piepho xyzzy at speakeasy.org
Sun Mar 11 09:40:17 CET 2007


I've been looking into integrating fmd1216 tuner support fully into dvb-pll
and removing the various code used in some drivers.

I've mostly figured out what the effect will be on the various users of
fmd1216 tuners, but there is something I'm not sure of.

In dvb-pll, the frequency offset, which is the IF frequency the tuner will
output at, is set to 36.213333 MHz.  It looks like this code was written
about two years ago by Patrick as part of the reverse engineered cxusb
driver.

In saa7134-dvb, there is some totally different code from programming
fmd1216 tuners, and it uses an IF frequency of 36.13 MHz.

So, why the difference?

The fmd1216 datasheet says the DVB-T IF frequency is 36.13 MHz.  But the IF
frequency is something also determined by the demodulator.  There are
several different demods using a fmd1216.  The cx22702 is used by a number
of cards, the product brief says it uses an IF of 36.17 MHz or 44.1 MHz.
There is a card using an mt352, which is using 36.16667 MHz in this case
(no code to re-program the IF frequency registers).  There are also two
cards using the tda10046 demod, which according to the driver is using a
36.13 MHz IF.

It seems like 36.13 MHz (probably 36 1/8 rounded to two digits) or
36.16667 (clearly 36 1/6) are the correct values.

So where did 36.213333 MHz come from?  It is supposed to be 36.13 plus 1/2
of the 1/6 MHz step size?



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