On 08/10/15 03:01, Duan Andy wrote:
> From: Jonathan Cameron <ji...@kernel.org> Sent: Sunday, September 27, 2015
> 11:53 PM
>> To: Bhuvanchandra DV; linux-...@vger.kernel.org
>> Cc: ste...@agner.ch; maitysancha...@gmail.com; Duan Fugang-B38611;
>> knaac...@gmx.de; l...@metafoo.de; pme...@pmeerw.net; shawn....@linaro.org;
>> linux-kernel@vger.kernel.org; Duan Fugang-B38611
>> Subject: Re: [PATCH] vf610_adc: Fix internal temperature calculation
>>
>> On 23/09/15 14:43, Bhuvanchandra DV wrote:
>>> There is an observed temperature difference of ~20°C with the internal
>>> temperature reading and the temperature measured on SoC package.
>>> Existing calculations consider the typical values provided in
>>> datasheet. Those typical values are valid for VREFH_ADC at 3.0V.
>>> Voltage at 25°C is different for different VREFH_ADC voltages. With
>>> VREFH_ADC at 3.3V, voltage at 25°C is 0.699V. Hence update the VTEMP25
>>> to 0.699V which gives ADCR@Temp25 as 867 and the final temperature
>>> readings differs with ~5°C from the external readings.
>>>
>>> Formula for finding ADCR@Temp25:
>>> ADCR@Temp25 = (ADCR@Vdd * V@TEMP25 * 10) / VDDconv
>>>
>>> ADCR@Vdd for 12-Bit ADC = 4095
>>> VDDconv = VREFH_ADC * 10
>>>
>>> VREFH_ADC@3.3V
>>> ADCR@Temp25 = (4095 * .699 * 10) / 33
>>> ADCR@Temp25 ~= 867
>>>
>>> | VREFH_ADC | V@TEMP25 | VDDconv | ADCR@Temp25 |
>>> | 3.0V | 0.696mV | 30 | 950 |
>>> | 3.3V | 0.699mV | 33 | 867 |
>>>
>>> Signed-off-by: Bhuvanchandra DV <bhuvanchandra...@toradex.com>
>> Looks fine to me, but I'll need an Ack from Fugang on this one as I don't
>> know or have the part I'm afraid.
>>
>> Jonathan
>
> The patch is fine for me. Sorry for the late response due to vacation.
>
> Acked-by: Fugang Duan <b38...@freescale.com>
Applied to the fixes-togreg branch of iio.git and marked for stable.
Thanks,
Jonathan
>
>>> ---
>>> drivers/iio/adc/vf610_adc.c | 19 ++++++++++++++-----
>>> 1 file changed, 14 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/iio/adc/vf610_adc.c b/drivers/iio/adc/vf610_adc.c
>>> index f4df2a7..e7abc13 100644
>>> --- a/drivers/iio/adc/vf610_adc.c
>>> +++ b/drivers/iio/adc/vf610_adc.c
>>> @@ -103,6 +103,13 @@
>>>
>>> #define DEFAULT_SAMPLE_TIME 1000
>>>
>>> +/* V at 25°C of 696 mV */
>>> +#define VF610_VTEMP25_3V0 950
>>> +/* V at 25°C of 699 mV */
>>> +#define VF610_VTEMP25_3V3 867
>>> +/* Typical sensor slope coefficient at all temperatures */
>>> +#define VF610_TEMP_SLOPE_COEFF 1840
>>> +
>>> enum clk_sel {
>>> VF610_ADCIOC_BUSCLK_SET,
>>> VF610_ADCIOC_ALTCLK_SET,
>>> @@ -636,11 +643,13 @@ static int vf610_read_raw(struct iio_dev
>> *indio_dev,
>>> break;
>>> case IIO_TEMP:
>>> /*
>>> - * Calculate in degree Celsius times 1000
>>> - * Using sensor slope of 1.84 mV/°C and
>>> - * V at 25°C of 696 mV
>>> - */
>>> - *val = 25000 - ((int)info->value - 864) * 1000000 /
>> 1840;
>>> + * Calculate in degree Celsius times 1000
>>> + * Using the typical sensor slope of 1.84 mV/°C
>>> + * and VREFH_ADC at 3.3V, V at 25°C of 699 mV
>>> + */
>>> + *val = 25000 - ((int)info->value - VF610_VTEMP25_3V3) *
>>> + 1000000 / VF610_TEMP_SLOPE_COEFF;
>>> +
>>> break;
>>> default:
>>> mutex_unlock(&indio_dev->mlock);
>>>
--
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