[linux-dvb] pcHDTV HD2000 card (ATSC) driver

Johannes Stezenbach js at linuxtv.org
Sat Feb 19 22:01:19 CET 2005

Rusty Scott wrote:
> Isn't that essentially what this code is doing? (providing relative values
> between 0x0000 and 0xFFFF)  The log calculation provides relative values for
> those that don't care and a % of a 30dB signal for those that do care.  I don't
> think we should remove value from those cards that can provide information
> simply because "most cards" can't or don't.
> I'm not sold on factoring it out to dvb-frontend unless there is another card
> that wants it outside of the HD2000 and HD3000.  These cards are from the same
> manufacturer and use similar demodulation chips, so naturally they would use
> the same functions.  My personal preference is to factor the code at the third
> duplication.

A fair number of demods provide signal strength values which are
linear, and we should really deliver a logarithmic value (dB)
to user space. But IMHO you can't get accurate values from
consumer equipment, I think this is what Holger meant. So far
we just delivered raw values from the hardware (possibly scaled
from 8bit to 16bit) to userspace,and it worked surprisingly well.
So, the question is if it is worth it to take the logarithm (it
should be in theory), and if yes, is your log function
general purpose (i.e. does it take a linear u16 in range 0-0xffff
and return a logarthmic value in range 0-0xffff), so it can be used
for any other demod.

> I will provide a "clean-up" patch with the rest of Johannes' suggestions but for
> now will leave the strength code where it is.

That's OK, someone else will take care of it if it matters.


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