On 28, April 2018 17:35, Jonathan Cameron wrote:
> On Sat, 28 Apr 2018 18:23:44 +0100
> Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
>
>> On Mon, 23 Apr 2018 00:03:59 +0200
>> David Veenstra <davidjulianveenstra@xxxxxxxxx> wrote:
>>
>> > The sysfs iio ABI states radians per second is expected as the unit for
>> > angular velocity, but the 12-bit angular velocity register has rps
>> Really small point, but rps is a bit ambiguous given we are
>> talking about converting to radian's per second ;)
>>
>> revs is the 'common' name for what it currently is I think.
>>
>> Otherwise this looks good.
> Actually, I can't immediately tell from the datasheet what the scaling is...
>
> "Bit 15 through bit 4 correspond to the angular
> information. The angular position data format is unsigned
> binary, with all zeros corresponding to 0 degrees and all ones
> corresponding to 360 degrees –l LSB. The angular velocity data
> format instead is twos complement binary, with the MSB
> representing the rotation direction"
>
> Earlier was also had:
>
> "Data Format
> The digital angle signal represents the absolute position of the
> resolver shaft as a 12-bit unsigned binary word. The digital
> velocity signal is a 12-bit twos complement word, which
> represents the velocity of the resolver shaft rotating in either a
> clockwise or a counterclockwise direction."
>
> So for position the 12 bits correspond to 0 to 360 - 360/(2^12)
> hence _SCALE is 360/(2^12)
>
> But I'm not seeing any hint whatsoever on the scaling for the
> rotational velocity...
>
> Am I missing it somewhere? you might be right in how you have
> read it given it will track up to 1000rps and we are 2 directional
> so -2048 to 2047 so not a huge amount of wasted space.
>
> Failing any other evidence I'll go with what you have until we
> can test this, but the datasheet could be clearer!
When I first read the datasheet it wasn't clear to me either. So I
emailed Michael Hennerich. He confirmed to me that the scaling factor
for degrees is indeed 360 / (2^12- 1). And he told me that the unit
for angular velocity is revolutions per second, and that I should
use a scaling factor of 2PI to convert it to rad/s.
Best regards,
David Veenstra
>
> Jonathan
>>
>> Jonathan
>>
>>
>> > as its unit. So a scaling factor of approximately 2 * Pi is
>> > added to the angular velocity channel.
>> >
>> > Signed-off-by: David Veenstra <davidjulianveenstra@xxxxxxxxx>
>> > ---
>> > Changes in v3:
>> > - A decimal approximation of the scale is used, instead
>> > of a fractional approximation.
>> > - Remove unneeded explanation of iio_convert_raw_to_processed.
>> >
>> > drivers/staging/iio/resolver/ad2s1200.c | 71 +++++++++++++++++++++------------
>> > 1 file changed, 45 insertions(+), 26 deletions(-)
>> >
>> > diff --git a/drivers/staging/iio/resolver/ad2s1200.c b/drivers/staging/iio/resolver/ad2s1200.c
>> > index 3c7163610ff6..3e1696e52c38 100644
>> > --- a/drivers/staging/iio/resolver/ad2s1200.c
>> > +++ b/drivers/staging/iio/resolver/ad2s1200.c
>> > @@ -57,37 +57,55 @@ static int ad2s1200_read_raw(struct iio_dev *indio_dev,
>> > struct ad2s1200_state *st = iio_priv(indio_dev);
>> > int ret = 0;
>> >
>> > - mutex_lock(&st->lock);
>> > - gpiod_set_value(st->sample, 0);
>> > -
>> > - /* delay (6 * AD2S1200_TSCLK + 20) nano seconds */
>> > - udelay(1);
>> > - gpiod_set_value(st->sample, 1);
>> > - gpiod_set_value(st->rdvel, !!(chan->type == IIO_ANGL));
>> > -
>> > - ret = spi_read(st->sdev, &st->rx, 2);
>> > - if (ret < 0) {
>> > + switch (m) {
>> > + case IIO_CHAN_INFO_SCALE:
>> > + switch (chan->type) {
>> > + case IIO_ANGL_VEL:
>> > + /* 2 * Pi ~= 6.283185 */
>> > + *val = 6;
>> > + *val2 = 283185;
>> > + return IIO_VAL_INT_PLUS_MICRO;
>> > + default:
>> > + return -EINVAL;
>> > + }
>> > + break;
>> > + case IIO_CHAN_INFO_RAW:
>> > + mutex_lock(&st->lock);
>> > + gpiod_set_value(st->sample, 0);
>> > +
>> > + /* delay (6 * AD2S1200_TSCLK + 20) nano seconds */
>> > + udelay(1);
>> > + gpiod_set_value(st->sample, 1);
>> > + gpiod_set_value(st->rdvel, !!(chan->type == IIO_ANGL));
>> > +
>> > + ret = spi_read(st->sdev, &st->rx, 2);
>> > + if (ret < 0) {
>> > + mutex_unlock(&st->lock);
>> > + return ret;
>> > + }
>> > +
>> > + switch (chan->type) {
>> > + case IIO_ANGL:
>> > + *val = be16_to_cpup(&st->rx) >> 4;
>> > + break;
>> > + case IIO_ANGL_VEL:
>> > + *val = sign_extend32(be16_to_cpup(&st->rx) >> 4, 11);
>> > + break;
>> > + default:
>> > + mutex_unlock(&st->lock);
>> > + return -EINVAL;
>> > + }
>> > +
>> > + /* delay (2 * AD2S1200_TSCLK + 20) ns for sample pulse */
>> > + udelay(1);
>> > mutex_unlock(&st->lock);
>> > - return ret;
>> > - }
>> >
>> > - switch (chan->type) {
>> > - case IIO_ANGL:
>> > - *val = be16_to_cpup(&st->rx) >> 4;
>> > - break;
>> > - case IIO_ANGL_VEL:
>> > - *val = sign_extend32(be16_to_cpup(&st->rx) >> 4, 11);
>> > - break;
>> > + return IIO_VAL_INT;
>> > default:
>> > - mutex_unlock(&st->lock);
>> > - return -EINVAL;
>> > + break;
>> > }
>> >
>> > - /* delay (2 * AD2S1200_TSCLK + 20) ns for sample pulse */
>> > - udelay(1);
>> > - mutex_unlock(&st->lock);
>> > -
>> > - return IIO_VAL_INT;
>> > + return -EINVAL;
>> > }
>> >
>> > static const struct iio_chan_spec ad2s1200_channels[] = {
>> > @@ -101,6 +119,7 @@ static const struct iio_chan_spec ad2s1200_channels[] = {
>> > .indexed = 1,
>> > .channel = 0,
>> > .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
>> > + .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
>> > }
>> > };
>> >
>>
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