Hi Fugang,
On 09/27/2015 09:23 PM, Jonathan Cameron wrote:
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.
Can you please give your ACK if the patch looks fine.
Best regards,
Bhuvan
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);
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
