On 11/10/15 15:05, Jonathan Cameron wrote:
> On 08/10/15 03:01, Duan Andy wrote:
>> From: Jonathan Cameron <jic23@xxxxxxxxxx> Sent: Sunday, September 27, 2015 11:53 PM
>>> To: Bhuvanchandra DV; linux-iio@xxxxxxxxxxxxxxx
>>> Cc: stefan@xxxxxxxx; maitysanchayan@xxxxxxxxx; Duan Fugang-B38611;
>>> knaack.h@xxxxxx; lars@xxxxxxxxxx; pmeerw@xxxxxxxxxx; shawn.guo@xxxxxxxxxx;
>>> linux-kernel@xxxxxxxxxxxxxxx; 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.dv@xxxxxxxxxxx>
>>> 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 <B38611@xxxxxxxxxxxxx>
> Applied to the fixes-togreg branch of iio.git and marked for stable.
> Thanks,
> Jonathan
Actually, change of plan. I'll hold this until Stefan's query is answered.
(naughty me - I hadn't read the whole thread!)
>>
>>>> ---
>>>> 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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