The ADC conversion is actually not rail-to-rail but with a factor 1.5.
Make use of this factor when calculating actual voltage.
Fixes: 3a89b289df5d ("iio: adc: add support for mcp3911")
Signed-off-by: Marcus Folkesson <[email protected]>
Acked-by: Jonathan Cameron <[email protected]>
---
drivers/iio/adc/mcp3911.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/drivers/iio/adc/mcp3911.c b/drivers/iio/adc/mcp3911.c
index f8875076ae80..890af7dca62d 100644
--- a/drivers/iio/adc/mcp3911.c
+++ b/drivers/iio/adc/mcp3911.c
@@ -40,8 +40,8 @@
#define MCP3911_CHANNEL(x) (MCP3911_REG_CHANNEL0 + x * 3)
#define MCP3911_OFFCAL(x) (MCP3911_REG_OFFCAL_CH0 + x * 6)
-/* Internal voltage reference in uV */
-#define MCP3911_INT_VREF_UV 1200000
+/* Internal voltage reference in mV */
+#define MCP3911_INT_VREF_MV 1200
#define MCP3911_REG_READ(reg, id) ((((reg) << 1) | ((id) << 5) | (1 << 0)) & 0xff)
#define MCP3911_REG_WRITE(reg, id) ((((reg) << 1) | ((id) << 5) | (0 << 0)) & 0xff)
@@ -139,11 +139,18 @@ static int mcp3911_read_raw(struct iio_dev *indio_dev,
*val = ret / 1000;
} else {
- *val = MCP3911_INT_VREF_UV;
+ *val = MCP3911_INT_VREF_MV;
}
- *val2 = 24;
- ret = IIO_VAL_FRACTIONAL_LOG2;
+ /*
+ * For 24bit Conversion
+ * Raw = ((Voltage)/(Vref) * 2^23 * Gain * 1.5
+ * Voltage = Raw * (Vref)/(2^23 * Gain * 1.5)
+ */
+
+ /* val2 = (2^23 * 1.5) */
+ *val2 = 12582912;
+ ret = IIO_VAL_FRACTIONAL;
break;
}
--
2.36.1
On Mon, 4 Jul 2022 19:21:10 +0200
Marcus Folkesson <[email protected]> wrote:
> The ADC conversion is actually not rail-to-rail but with a factor 1.5.
> Make use of this factor when calculating actual voltage.
>
> Fixes: 3a89b289df5d ("iio: adc: add support for mcp3911")
> Signed-off-by: Marcus Folkesson <[email protected]>
> Acked-by: Jonathan Cameron <[email protected]>
? I doubt I gave a tag (mostly because I don't give tags to patches
I'll pick up and give a SoB on.
Note that tags have to be given explicitly in full form before you can
add them to a patch. If in doubt (people often given handwavey responses)
then ask people to give an explicit tag.
Jonathan
> ---
> drivers/iio/adc/mcp3911.c | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/iio/adc/mcp3911.c b/drivers/iio/adc/mcp3911.c
> index f8875076ae80..890af7dca62d 100644
> --- a/drivers/iio/adc/mcp3911.c
> +++ b/drivers/iio/adc/mcp3911.c
> @@ -40,8 +40,8 @@
> #define MCP3911_CHANNEL(x) (MCP3911_REG_CHANNEL0 + x * 3)
> #define MCP3911_OFFCAL(x) (MCP3911_REG_OFFCAL_CH0 + x * 6)
>
> -/* Internal voltage reference in uV */
> -#define MCP3911_INT_VREF_UV 1200000
> +/* Internal voltage reference in mV */
> +#define MCP3911_INT_VREF_MV 1200
>
> #define MCP3911_REG_READ(reg, id) ((((reg) << 1) | ((id) << 5) | (1 << 0)) & 0xff)
> #define MCP3911_REG_WRITE(reg, id) ((((reg) << 1) | ((id) << 5) | (0 << 0)) & 0xff)
> @@ -139,11 +139,18 @@ static int mcp3911_read_raw(struct iio_dev *indio_dev,
>
> *val = ret / 1000;
> } else {
> - *val = MCP3911_INT_VREF_UV;
> + *val = MCP3911_INT_VREF_MV;
> }
>
> - *val2 = 24;
> - ret = IIO_VAL_FRACTIONAL_LOG2;
> + /*
> + * For 24bit Conversion
> + * Raw = ((Voltage)/(Vref) * 2^23 * Gain * 1.5
> + * Voltage = Raw * (Vref)/(2^23 * Gain * 1.5)
> + */
> +
> + /* val2 = (2^23 * 1.5) */
> + *val2 = 12582912;
> + ret = IIO_VAL_FRACTIONAL;
> break;
> }
>
Hi,
On Sat, Jul 16, 2022 at 06:18:37PM +0100, Jonathan Cameron wrote:
> On Mon, 4 Jul 2022 19:21:10 +0200
> Marcus Folkesson <[email protected]> wrote:
>
> > The ADC conversion is actually not rail-to-rail but with a factor 1.5.
> > Make use of this factor when calculating actual voltage.
> >
> > Fixes: 3a89b289df5d ("iio: adc: add support for mcp3911")
> > Signed-off-by: Marcus Folkesson <[email protected]>
> > Acked-by: Jonathan Cameron <[email protected]>
> ? I doubt I gave a tag (mostly because I don't give tags to patches
> I'll pick up and give a SoB on.
>
> Note that tags have to be given explicitly in full form before you can
> add them to a patch. If in doubt (people often given handwavey responses)
> then ask people to give an explicit tag.
Sorry for that. I will remove the tag.
I interpreted your "Otherwise looks good to me." as an acked-by.
I will only go for explicit tags forward.
Thanks,
Marcus Folkesson
>
> Jonathan