[linux-dvb] [RFC] SNR units in tuners

Andreas Oberritter obi at linuxtv.org
Sun Oct 19 13:46:12 CEST 2008

Matthias Schwarzott wrote:
> On Freitag, 17. Oktober 2008, Devin Heitmueller wrote:
>> Hello,
>> In response to Steven Toth's suggestion regarding figuring out what
>> the various units are across demodulators, I took a quick inventory
>> and came up with the following list.  Note that this is just a first
>> pass by taking a quick look at the source for each demodulator (I
>> haven't looked for the datasheets for any of them yet or done sample
>> captures to see what the reported ranges are).
>> Could everybody who is responsible for a demod please take a look at
>> the list and see if you can fill in the holes?
>> Having a definitive list of the current state is important to being
>> able to provide unified reporting of SNR.
>> Thank you,
>> Devin
>> mt312.c         unknown
> The hardware provides two values:
> * AGC: For now the AGC feedback value (14 bit) is returned unchanged.
> * ERR_db: Also available is a 10-bit value representing the signal level 
> difference between AGC-Reference and received signal level (most likely in 
> 1dB steps).
> If an absolute value is needed: I don't get it how to calc absolute signal 
> levels from AGC-Reference.
> so code for now:
> mt312.c: agc-feedback 0-0x3FFF
> @Obi:
> Any additions?

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