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
as its unit. So a fractional scaling factor of approximately 2 * Pi is
added to the angular velocity channel.
The added comments will also be relevant for the scaling factor of
the angle channel.
Signed-off-by: David Veenstra <davidjulianveenstra@xxxxxxxxx>
---
Changes in v2:
- Move explanation of Pi approximation to top of switch statement,
as this will also be relevant to angle channel.
- Replaced 33102 / 2 with 16551 on line 84.
drivers/staging/iio/resolver/ad2s1200.c | 84 +++++++++++++++++++++++----------
1 file changed, 59 insertions(+), 25 deletions(-)
diff --git a/drivers/staging/iio/resolver/ad2s1200.c b/drivers/staging/iio/resolver/ad2s1200.c
index 29a9bb666e7b..6c56257be3b1 100644
--- a/drivers/staging/iio/resolver/ad2s1200.c
+++ b/drivers/staging/iio/resolver/ad2s1200.c
@@ -60,38 +60,71 @@ static int ad2s1200_read_raw(struct iio_dev *indio_dev,
int ret = 0;
u16 vel;
- mutex_lock(&st->lock);
- gpiod_set_value(st->sample, 0);
+ /*
+ * Below a fractional approximation of Pi is needed.
+ * The following approximation will be used: 103993 / 33102.
+ * This is accurate in 9 decimals places.
+ *
+ * This fraction is based on OEIS series of nominator/denominator
+ * of convergents to Pi (A002485 and A002486).
+ */
+ switch (m) {
+ case IIO_CHAN_INFO_SCALE:
+ switch (chan->type) {
+ case IIO_ANGL_VEL:
+ /*
+ * 2 * Pi ~= 2 * 103993 / 33102
+ *
+ * iio_convert_raw_to_processed uses integer
+ * division. This will cause at most 5% error
+ * (for very small values). But for 99.5% of the values
+ * it will cause less that 1% error.
+ */
+ *val = 103993;
+ *val2 = 16551;
+ return IIO_VAL_FRACTIONAL;
+ 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;
+ }
- /* delay (6 * AD2S1200_TSCLK + 20) nano seconds */
- udelay(1);
- gpiod_set_value(st->sample, 1);
- gpiod_set_value(st->rdvel, !!(chan->type == IIO_ANGL));
+ vel = be16_to_cpup((__be16 *)st->rx);
+ switch (chan->type) {
+ case IIO_ANGL:
+ *val = vel >> 4;
+ break;
+ case IIO_ANGL_VEL:
+ *val = sign_extend32((s16)vel >> 4, 11);
+ break;
+ default:
+ mutex_unlock(&st->lock);
+ return -EINVAL;
+ }
- ret = spi_read(st->sdev, st->rx, 2);
- if (ret < 0) {
+ /* delay (2 * AD2S1200_TSCLK + 20) ns for sample pulse */
+ udelay(1);
mutex_unlock(&st->lock);
- return ret;
- }
- vel = be16_to_cpup((__be16 *)st->rx);
- switch (chan->type) {
- case IIO_ANGL:
- *val = vel >> 4;
- break;
- case IIO_ANGL_VEL:
- *val = sign_extend32((s16)vel >> 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[] = {
@@ -105,6 +138,7 @@ 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),
}
};
--
2.16.2
--
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