On Tue, May 31, 2016 at 10:45 AM, Alison Schofield <amsfield22@xxxxxxxxx> wrote:
> On Sun, May 29, 2016 at 07:53:08PM -0700, Matt Ranostay wrote:
>> Alison,
>>
>> Can you give a Tested-by: since I don't own this sensor anymore.
>>
>> Thanks,
>>
>> Matt
>
> Tested it. Verified temp & humidty calcs. Looks great!
>
> And, (seeing a pattern here ;)) this comes with another question,
> probably directed a Jonathan...
>
> with regards to temperature calculations:
>
> Datasheets give numbers for this method:
> temp = ((raw * scale) + offset)
> IIO drivers report numbers for this method:
> temp = ((raw + offset) * scale)
>
We do it this way in iio.. hence why the offset needs the scaling
value applied to it.
> I've figured out the math for translating between them and creating
> the offset for the driver to report in sysfs, but don't know why we
> are doing that. 'Our' way seems kind of ugly. For example, for HDC1008
> the offset is -40. It's the minimum expected temp value. But, we munge
> it to be -15887.515151 so we can apply it before scaling.
>
> Why do we do it this way in IIO?
>
> alisons
>
>>
>> On Sun, May 29, 2016 at 7:52 PM, Matt Ranostay <mranostay@xxxxxxxxx> wrote:
>> > Shifting sensor data to the right 2 bits was incorrect and caused the
>> > scaling values + offsets to be invalid.
>> >
>> > Reported-by: Alison Schofield <amsfield22@xxxxxxxxx>
>> > Signed-off-by: Matt Ranostay <mranostay@xxxxxxxxx>
>> > ---
>> > drivers/iio/humidity/hdc100x.c | 16 ++++++++--------
>> > 1 file changed, 8 insertions(+), 8 deletions(-)
>> >
>> > diff --git a/drivers/iio/humidity/hdc100x.c b/drivers/iio/humidity/hdc100x.c
>> > index 3070983..a03832a 100644
>> > --- a/drivers/iio/humidity/hdc100x.c
>> > +++ b/drivers/iio/humidity/hdc100x.c
>> > @@ -164,14 +164,14 @@ static int hdc100x_get_measurement(struct hdc100x_data *data,
>> > dev_err(&client->dev, "cannot read high byte measurement");
>> > return ret;
>> > }
>> > - val = ret << 6;
>> > + val = ret << 8;
>> >
>> > ret = i2c_smbus_read_byte(client);
>> > if (ret < 0) {
>> > dev_err(&client->dev, "cannot read low byte measurement");
>> > return ret;
>> > }
>> > - val |= ret >> 2;
>> > + val |= ret;
>> >
>> > return val;
>> > }
>> > @@ -212,17 +212,17 @@ static int hdc100x_read_raw(struct iio_dev *indio_dev,
>> > case IIO_CHAN_INFO_SCALE:
>> > if (chan->type == IIO_TEMP) {
>> > *val = 165000;
>> > - *val2 = 65536 >> 2;
>> > + *val2 = 65536;
>> > return IIO_VAL_FRACTIONAL;
>> > } else {
>> > - *val = 0;
>> > - *val2 = 10000;
>> > - return IIO_VAL_INT_PLUS_MICRO;
>> > + *val = 100;
>> > + *val2 = 65536;
>> > + return IIO_VAL_FRACTIONAL;
>> > }
>> > break;
>> > case IIO_CHAN_INFO_OFFSET:
>> > - *val = -3971;
>> > - *val2 = 879096;
>> > + *val = -15887;
>> > + *val2 = 515151;
>> > return IIO_VAL_INT_PLUS_MICRO;
>> > default:
>> > return -EINVAL;
>> > --
>> > 2.7.4
>> >
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