Currently IIO uses a decimal fixed point representations for real type numbers.
This patch introduces a new representation for rational type numbers. The number
will be expressed by specifying a numerator and denominator. For converting a
raw value to a processed value multiply it by the numerator and divide it by the
denominator.
The reasoning for introducing this new type is that for a lot of devices the
scale can be represented easily by a fractional number, but it is not possible
to represent it as fixed point number without rounding. E.g. for a simple DAC
the scale is often the reference voltage divided by the number of possible
values (Usually 2**n_bits - 1). Each driver currently implements the conversion
of this fraction to a fixed point number on its own.
Also when it comes to the in-kernel interface this allows to directly use the
fractional factors to convert a raw value to a processed value. This should on
one hand require less instructions and on the other hand increase the
precession.
Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
---
drivers/iio/industrialio-core.c | 6 ++++++
include/linux/iio/types.h | 1 +
2 files changed, 7 insertions(+)
diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 0499330..6eb24db 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -366,6 +366,7 @@ static ssize_t iio_read_channel_info(struct device *dev,
{
struct iio_dev *indio_dev = dev_to_iio_dev(dev);
struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
+ unsigned long long tmp;
int val, val2;
bool scale_db = false;
int ret = indio_dev->info->read_raw(indio_dev, this_attr->c,
@@ -391,6 +392,11 @@ static ssize_t iio_read_channel_info(struct device *dev,
return sprintf(buf, "-%d.%09u\n", val, -val2);
else
return sprintf(buf, "%d.%09u\n", val, val2);
+ case IIO_VAL_FRACTIONAL:
+ tmp = div_s64((s64)val * 1000000000LL, val2);
+ val2 = do_div(tmp, 1000000000LL);
+ val = tmp;
+ return sprintf(buf, "%d.%09u\n", val, val2);
default:
return 0;
}
diff --git a/include/linux/iio/types.h b/include/linux/iio/types.h
index 44e3977..5c647ec 100644
--- a/include/linux/iio/types.h
+++ b/include/linux/iio/types.h
@@ -57,5 +57,6 @@ enum iio_modifier {
#define IIO_VAL_INT_PLUS_MICRO 2
#define IIO_VAL_INT_PLUS_NANO 3
#define IIO_VAL_INT_PLUS_MICRO_DB 4
+#define IIO_VAL_FRACTIONAL 10
#endif /* _IIO_TYPES_H_ */
--
1.7.10.4
--
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
