[linux-dvb] DVB API update
abraham.manu at gmail.com
Tue Sep 18 04:25:02 CEST 2007
Johannes Stezenbach wrote:
> On Sat, Sep 15, 2007, Wolfgang Wegner wrote:
>> - dvb_fe_type: DVB-S2 is missing and I personally would also like
>> to see ASI here...
> See my other mail, IMHO we should add the ASI defines at
> the same time we merge a driver which uses it.
>> - frontend status:
>> - BER is lacking a proper definition (to which base is it calculated?)
>> - signal strength: same problem, what are the ranges?
>> - snr: again, no base and ranges given
> The original Nokia DVB API spec had proper definitions, but
> Holger Waechtler and me decided to drop them in favour of
> "read hw register and scale to range 0..0xffff". The reasons
> for this were:
> - for some hw we didn't have info to implement it properly
> - for those hw where we had info we saw it wasn't worth the
> effort -- I believe the implementation in the demod firmware
> is just such a coarse approximation that it doesn't
> even make a difference if you take the logarithm or not
> (provided you scale back into the 16bit range)
> (of course you get different numbers, but none of them
> maps any better to what you'd expect)
As an example, BER is not just a dump of some registers. It depends on
the symbols being acquired, averaged etc. If you have a lower symbol
rate, you have a larger acquisition time frame, also lower the symbols,
the larger the number of snapshots required for proper averaging.
Also when you start a measurement, all of it has to be ideally at the
same snapshot of time, eventhough you can't get the exact same snapshot,
you must be somewhere quite near.
Just take a look over here:
No wonder it is so hopeless.
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