| From | Kamal Mostafa <> | Subject | [PATCH 3.19.y-ckt 001/128] vf610_adc: Fix internal temperature calculation | Date | Wed, 16 Dec 2015 09:37:21 -0800 |
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3.19.8-ckt12 -stable review patch. If anyone has any objections, please let me know.
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From: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
commit 6219f432ec037317a77c40910da12a626c34af1c upstream.
Calculate ADCR_VTEMP25 using VTEMP25 at VREFH_ADC 3V3. Existing calculations consider the typical values provided in datasheet. Those typical values are valid for VREFH_ADC at 3.0V. VTEMP25 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.
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@toradex.com> Acked-by: Fugang Duan <B38611@freescale.com> Signed-off-by: Jonathan Cameron <jic23@kernel.org> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- 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 60617ed..cf56404 100644 --- a/drivers/iio/adc/vf610_adc.c +++ b/drivers/iio/adc/vf610_adc.c @@ -98,6 +98,13 @@ #define VF610_ADC_CALF 0x2 #define VF610_ADC_TIMEOUT msecs_to_jiffies(100) +/* 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, @@ -513,11 +520,13 @@ 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); -- 1.9.1
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