Re: [PATCH] thermal: generic-adc: Fix linear temperature approximation

["Paweł Jarosz" <paweljarosz3691@gmail.com>]

W dniu 21.10.2016 o 08:18, Laxman Dewangan pisze:
>
> On Thursday 20 October 2016 10:56 PM, Paweł Jarosz wrote:
>>
>>> It is Negative Coefficient Thermistor (NCT) and so adc reads are 
>>> different.
>>> Lower temp gives higher value.
>>>
>>> So table should be
>>>
>>> <7000 10
>>> 9000 8>;
>>>
>>> temp1 = gti->lookup_table[2 * i];
>>> temp2 = gti->lookup_table[2 * i - 2];
>>>
>>> and then use in following equation.
>>>
>>>>
>>>>     adc_hi = gti->lookup_table[2 * i - 1];
>>>>     adc_lo = gti->lookup_table[2 * i + 1];
>>>>     temp = gti->lookup_table[2 * i];
>>>>     temp -= (val - adc_lo) * (temp1 - temp2) / (adc_hi - adc_lo);
>>
>> val = 9
>> adc_hi = 10
>> adc_lo = 8
>> temp = 9000 - (9 - 8)*(7000 - 9000)/(10 - 8)
>> temp = 9000 - (1)*(-2000)/(2)
>>
>> temp = 9000 - (-1000) = 10000
>>
>> still wrong ... temp for val = 9 should be 8000
>
>
> Your temp1 and temp2 calculation is something wrong.
>
> temp1 = gti->lookup_table[2 * i];
> temp2 = gti->lookup_table[2 * i - 2];
> so temp1 = 9000, temp2 = 7000
>
There was nothing wrong with my calculation but you changed the order to 
fix your equation.

You can send the patch.


Paweł