Re: [PATCH] stv090x: use lookup tables for carrier/noise ratio

[Joerg Riechardt <J.Riechardt@gmx.de>]

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Am 11.11.2014 um 11:28 schrieb Mauro Carvalho Chehab:
> Em Wed, 18 Sep 2013 01:05:20 +0200
> Joerg Riechardt <J.Riechardt@gmx.de> escreveu:
>
>> The stv090x driver uses the lookup table for signal strength already,
>> with this patch we use the lookup tables for carrier/noise ratio as well.
>> This has the advantage, that values for DVB-S and DVB-S2 are now
>> corresponding, while before they were way off. The values are now
>> proportional to real carrier/noise ratio, while before they were
>> corresponding to register values. So now applications are able to give
>> the user real carrier/noise ratio.
>>
>> Because the output has to be within 0x0000...0xFFFF the three negative
>> values for DVB-S2 are omitted. This is no significant loss, because
>> reception is lost at 7.5 dB already (TT S2-1600, Cine S2), so the
>> negative values are not really important, and also for DVB-S they don´t
>> exist.
>>
>> Signed-off-by: Joerg Riechardt <j.riechardt@gmx.de>
>>
>> Regards,
>> Joerg
>>
>> --- stv090x.c.bak	2013-09-06 20:59:01.132365872 +0200
>> +++ stv090x.c	2013-09-10 03:21:48.884115191 +0200
>> @@ -173,9 +173,9 @@
>>
>>   /* DVBS2 C/N Lookup table */
>>   static const struct stv090x_tab stv090x_s2cn_tab[] = {
>> -	{ -30, 13348 }, /* -3.0dB */
>> -	{ -20, 12640 }, /* -2d.0B */
>> -	{ -10, 11883 }, /* -1.0dB */
>> +//	{ -30, 13348 }, /* -3.0dB */
>> +//	{ -20, 12640 }, /* -2d.0B */
>> +//	{ -10, 11883 }, /* -1.0dB */
>>   	{   0, 11101 }, /* -0.0dB */
>>   	{   5, 10718 }, /*  0.5dB */
>>   	{  10, 10339 }, /*  1.0dB */
>
> Instead of commenting, just truncate the value at the DVBv3 stats
> function.

Ok, done.
Changed patch attached.

>
>> @@ -3697,9 +3697,10 @@
>>   			}
>>   			val /= 16;
>>   			last = ARRAY_SIZE(stv090x_s2cn_tab) - 1;
>> -			div = stv090x_s2cn_tab[0].read -
>> -			      stv090x_s2cn_tab[last].read;
>> -			*cnr = 0xFFFF - ((val * 0xFFFF) / div);
>> +			div = stv090x_s2cn_tab[last].real -
>> +			      stv090x_s2cn_tab[0].real;
>> +			val = stv090x_table_lookup(stv090x_s2cn_tab, last, val);
>> +			*cnr = val * 0xFFFF / div;
>>   		}
>>   		break;
>>
>> @@ -3719,9 +3720,10 @@
>>   			}
>>   			val /= 16;
>>   			last = ARRAY_SIZE(stv090x_s1cn_tab) - 1;
>> -			div = stv090x_s1cn_tab[0].read -
>> -			      stv090x_s1cn_tab[last].read;
>> -			*cnr = 0xFFFF - ((val * 0xFFFF) / div);
>> +			div = stv090x_s1cn_tab[last].real -
>> +			      stv090x_s1cn_tab[0].real;
>> +			val = stv090x_table_lookup(stv090x_s1cn_tab, last, val);
>> +			*cnr = val * 0xFFFF / div;
>>   		}
>
> As, with this patch, C/N will be a properly scaled value, the best
> is to add support for DVBv5 stats. With DVBv5 stats, the scale can
> be sent to userspace.

Sorry, I have no plans to add DVBv5 stats, although I agree, it would be 
nice, if someone did.

Signed-off-by: Joerg Riechardt <j.riechardt@gmx.de>

Regards,
Joerg


>
>>   		break;
>>   	default:
>
> Regards,
> Mauro
>

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diff -Nru A/stv090x.c B/stv090x.c
--- A/stv090x.c	2015-06-25 14:33:58.000000000 +0200
+++ B/stv090x.c	2015-08-29 16:07:44.889861230 +0200
@@ -3726,9 +3726,12 @@
 			}
 			val /= 16;
 			last = ARRAY_SIZE(stv090x_s2cn_tab) - 1;
-			div = stv090x_s2cn_tab[0].read -
-			      stv090x_s2cn_tab[last].read;
-			*cnr = 0xFFFF - ((val * 0xFFFF) / div);
+			div = stv090x_s2cn_tab[last].real -
+			      stv090x_s2cn_tab[3].real;
+			val = stv090x_table_lookup(stv090x_s2cn_tab, last, val);
+			if (val < 0)
+				val = 0;
+			*cnr = val * 0xFFFF / div;
 		}
 		break;
 
@@ -3748,9 +3751,10 @@
 			}
 			val /= 16;
 			last = ARRAY_SIZE(stv090x_s1cn_tab) - 1;
-			div = stv090x_s1cn_tab[0].read -
-			      stv090x_s1cn_tab[last].read;
-			*cnr = 0xFFFF - ((val * 0xFFFF) / div);
+			div = stv090x_s1cn_tab[last].real -
+			      stv090x_s1cn_tab[0].real;
+			val = stv090x_table_lookup(stv090x_s1cn_tab, last, val);
+			*cnr = val * 0xFFFF / div;
 		}
 		break;
 	default: