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iio: Introduce a new fractional value type

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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
precision.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
This commit is contained in:
Lars-Peter Clausen 2012-09-14 16:21:00 +01:00 committed by Jonathan Cameron
parent ca7d1b32d2
commit 7985e7c100
2 changed files with 7 additions and 0 deletions
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6
drivers/iio/industrialio-core.c
View file

@ -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;
}

1
include/linux/iio/types.h
View file

@ -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_ */