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| author | Lars-Peter Clausen <lars@metafoo.de> | 2012-09-14 17:21:00 +0200 |
|---|---|---|
| committer | Jonathan Cameron <jic23@kernel.org> | 2012-09-15 11:12:22 +0200 |
| commit | 7985e7c1003bc5cdfa20755f8cfdada946ed8e18 (patch) | |
| tree | 94adb3cf91ec3406361c2bc9d0c66485e1bf2436 /drivers/iio | |
| parent | iio: Documentation change for inkern interface. (diff) | |
| download | linux-7985e7c1003bc5cdfa20755f8cfdada946ed8e18.tar.xz linux-7985e7c1003bc5cdfa20755f8cfdada946ed8e18.zip | |
iio: Introduce a new fractional value type
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>
Diffstat (limited to 'drivers/iio')
| -rw-r--r-- | drivers/iio/industrialio-core.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c index 0499330d6e98..6eb24dbc081e 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; } |