On Wed, 14 Feb 2018 01:08:35 +0000
Richard Lai <richard@xxxxxxxxxxxxxx> wrote:
> The resistance member in ccs811_reading struct is an unsigned 16-bit
> integer variable used to store RAW_DATA register bytes read from CCS811.
> It is kind of misleading to name this struct member as resistance.
>
> About the RAW_DATA register bytes, the CCS811 datasheet states that:
> -----
> Two byte read only register which contains the latest readings from the
> sense resistor.
>
> The most significant 6 bits of the Byte 0 contain the value of the current
> through the sensor (0μA to 63μA).
>
> The lower 10 bits contain (as computed from the ADC) the readings of the
> voltage across the sensor with the selected current (1023 = 1.65V)"
> -----
>
> Hence, the RAW_DATA register byte contains information about electric
> current and voltage of the CCS811 sensor. Calling this struct member
> 'resistance' is kind of misleading, although both electric current and
> voltage are needed to calculate the electrical resistance of the sensor
> using Ohm's law, V = I x R, in which a new channel type of IIO_RESISTANCE
> may be added to the driver in the future.
>
> Signed-off-by: Richard Lai <richard@xxxxxxxxxxxxxx>
This seems logical to me, but I'd just like to let it sit for a few
more days to let Narcisa have time to respond.
Feel free to give me a poke if it looks like I have forgotten this
in a week or so.
Thanks,
Jonathan
> ---
> drivers/iio/chemical/ccs811.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iio/chemical/ccs811.c b/drivers/iio/chemical/ccs811.c
> index 8e8beb7..e6f6bc4 100644
> --- a/drivers/iio/chemical/ccs811.c
> +++ b/drivers/iio/chemical/ccs811.c
> @@ -66,7 +66,7 @@ struct ccs811_reading {
> __be16 voc;
> u8 status;
> u8 error;
> - __be16 resistance;
> + __be16 raw_data;
> } __attribute__((__packed__));
>
> struct ccs811_data {
> @@ -202,12 +202,12 @@ static int ccs811_read_raw(struct iio_dev *indio_dev,
>
> switch (chan->type) {
> case IIO_VOLTAGE:
> - *val = be16_to_cpu(data->buffer.resistance) &
> + *val = be16_to_cpu(data->buffer.raw_data) &
> CCS811_VOLTAGE_MASK;
> ret = IIO_VAL_INT;
> break;
> case IIO_CURRENT:
> - *val = be16_to_cpu(data->buffer.resistance) >> 10;
> + *val = be16_to_cpu(data->buffer.raw_data) >> 10;
> ret = IIO_VAL_INT;
> break;
> case IIO_CONCENTRATION:
--
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