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From: Martin Fuzzey <mfuzzey@parkeon.com>
To: linux-iio@vger.kernel.org, Jonathan Cameron <jic23@kernel.org>
Subject: [PATCH] iio: mma8452: Use correct acceleration units.
Date: Fri, 11 Jul 2014 14:54:31 +0200	[thread overview]
Message-ID: <20140711125431.22109.59659.stgit@localhost> (raw)

The userspace interface for acceleration sensors is documented as using
m/s^2 units [Documentation/ABI/testing/sysfs-bus-iio]

The fullscale raw value for the mma8452 (-2048) corresponds to -2G, -4G or -8G
depending on the seleted mode.

The scale table was converting to G rather than m/s^2.
Change the scaling table to match the documented interface.

Signed-off-by: Martin Fuzzey <mfuzzey@parkeon.com>
---
 drivers/iio/accel/mma8452.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
index 17aeea1..61eba5a 100644
--- a/drivers/iio/accel/mma8452.c
+++ b/drivers/iio/accel/mma8452.c
@@ -111,8 +111,13 @@ static const int mma8452_samp_freq[8][2] = {
 	{6, 250000}, {1, 560000}
 };
 
+/* Hardware has fullscale of -2G, -4G, -8G corresponding to raw value -2048
+ * The userspace interface uses m/s^2 and we declare micro units
+ * So scale factor is given by:
+ * 	g * N * 1000000 / 2048 for N = 2, 4, 8 and g=9.80665
+ */
 static const int mma8452_scales[3][2] = {
-	{0, 977}, {0, 1953}, {0, 3906}
+	{0, 9577}, {0, 19154}, {0, 38307}
 };
 
 static ssize_t mma8452_show_samp_freq_avail(struct device *dev,


             reply	other threads:[~2014-07-11 13:27 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-07-11 12:54 Martin Fuzzey [this message]
2014-07-12 10:50 ` [PATCH] iio: mma8452: Use correct acceleration units Hartmut Knaack
2014-07-12 12:19   ` Jonathan Cameron

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