On 05/10/15 06:57, Matt Ranostay wrote: > On Tue, Sep 29, 2015 at 10:33 AM, Jonathan Cameron <jic23@xxxxxxxxxx> wrote: >> 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 ;) > > Ok that works. Applied to the togreg branch of iio.git - initially pushed out as testing for the autobuilders to play with it. Thanks, Jonathan >> >> 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 > -- 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
