On 29/09/15 05:19, Matt Ranostay wrote: > On Mon, Sep 28, 2015 at 2:08 AM, Jonathan Cameron > <jic23@xxxxxxxxxxxxxxxxxxxxx> wrote: >> >> >> On 27 September 2015 23:35:29 BST, Matt Ranostay <mranostay@xxxxxxxxx> wrote: >>> On Sun, Sep 27, 2015 at 6:29 AM, Jonathan Cameron <jic23@xxxxxxxxxx> >>> wrote: >>>> On 27/09/15 07:18, Matt Ranostay wrote: >>>>> Previous offset wasn't applied in the correct order and invalid. >>>>> This patchset fixes this issue, and also has the correct scale value >>>>> applied to the offset. >>>>> >>>>> Signed-off-by: Matt Ranostay <mranostay@xxxxxxxxx> >>>> Oops, missed that. >>>> >>>> Given it's provided in the datasheet as effectively a fractional >>> value >>>> would val = -40000, val2 = 65536 and type = IIO_FRACTIONAL not be >>> cleaner >>>> and give the same answer? >>>> >>> Actually not because the way the datasheet states it ((value / 2**16) >>> * 165) - 40, so the scale value needs to be applied to the -40 >>> offset (165/65536) >> Good point. Can't we do (-40*165)/65536 ? > > Nope. > > scale = 165<<2 / 65536 > offset = 40 / scale > > Maybe we should add a new IIO_CHAN_INFO_SCALED_OFFSET that uses the > scale value and a divisor that returns an IIO_FRACTIONAL? Hmm. Would get messy fast. Lets just go with your original fixed point option below. If someone later figures out a neater way of doing it, good for them ;) J > > >>> >>>> Speaking of which, for the scale are we loosing any precision by >>> shifting >>>> the bottom of the fraction right 2 rather than the top left 2 which >>> would have >>>> the same result? >>> >>> Ah possibly. But I suspect isn't anything measurable... >>> >>>> >>>> Jonathan >>>>> --- >>>>> drivers/iio/humidity/hdc100x.c | 5 +++-- >>>>> 1 file changed, 3 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/drivers/iio/humidity/hdc100x.c >>> b/drivers/iio/humidity/hdc100x.c >>>>> index 2824578..a7f61e8 100644 >>>>> --- a/drivers/iio/humidity/hdc100x.c >>>>> +++ b/drivers/iio/humidity/hdc100x.c >>>>> @@ -221,8 +221,9 @@ static int hdc100x_read_raw(struct iio_dev >>> *indio_dev, >>>>> } >>>>> break; >>>>> case IIO_CHAN_INFO_OFFSET: >>>>> - *val = -40; >>>>> - return IIO_VAL_INT; >>>>> + *val = -3971; >>>>> + *val2 = 879096; >>>>> + return IIO_VAL_INT_PLUS_MICRO; >>>>> default: >>>>> return -EINVAL; >>>>> } >>>>> >>>> >> >> -- >> Sent from my Android device with K-9 Mail. Please excuse my brevity. -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
