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: http://www.dsprelated.com/showmessage/33285/1.php No wonder it is so hopeless. HTH Manu _______________________________________________ linux-dvb mailing list linux-dvb@xxxxxxxxxxx http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
