Re: [PATCH 1/5] rtl2832 ver 0.3: suport for RTL2832 demodulator revised version

[Antti Palosaari <crope@iki.fi>]

On 14.05.2012 04:37, Antti Palosaari wrote:
>
>> +    else {
>> +        /* if_agc is read as a 10bit binary */
>> +        ret = rtl2832_rd_demod_reg(priv, DVBT_IF_AGC_VAL,&if_agc_raw);
>> +        if (ret)
>> +            goto err;
>> +
>> +            if (if_agc_raw<  (1<<  9))
>> +                if_agc = if_agc_raw;
>> +            else
>> +                if_agc = -(~(if_agc_raw-1)&  0x1ff);
>> +
>> +            *strength = 55 - if_agc / 182;
>> +            *strength |= *strength<<  8;
>
> That calculation shows doubtful. Why not to scale directly to the
> counter. Now you divide it by 182 and after that multiply 256 (<< 8
> means same as multiply by 256). It is stupid calculation.

I was playing with RTL2830 statistics and thus it is quite similar I 
ended up looking that again. It is not so wrong as I commented. The idea 
of whole calculation is to underflow unsigned 8 bit value to the 
*strength. But it goes wrong here because you don't cast it as unsigned 
char (this should be *strength = (u8) (55 - if_agc / 182);.

I implemented that rather similarly for the RTL2830. But it is very poor 
resolution for some reason... :-(

regards
Antti
-- 
http://palosaari.fi/