[linux-dvb] [RFC] [PATCH] Make S/N values to appear at cx24123 frontend

Yeasah Pell yeasah at schwide.com
Mon Apr 17 06:11:01 CEST 2006


>So I think THIS is the curve you should be trying to use to convert BER to
>SNR.  The question I have it, what are the units of the 22-bit value read from
>the chip?  How do you convert this to the fraction of the bits in error?
>Divide by the gross bitrate (bandwidth in MHz times two)?
>  
>
The meaning of the 22-bit error counter value is configurable, but it's 
always a count of some type of error over a fixed window. Per the 
datasheet, the demod is currently configured by the driver to return a 
count of reed-solomon block errors with a window size of 65280 blocks 
(which is the maximum)

If the datasheet is accurate, I don't see how the value would ever be 
greater than 65280 given its configuration (since you can't have more 
than 100% of the blocks in the window bad), so we're only looking at 16 
bits of significance out of the 22. I assume the extra bits are there 
because you can request error rate for bytes or bits as well, which 
would give correspondingly greater maximum counts.




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