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authorMartin Kelly <mkelly@xevo.com>2018-05-21 11:41:54 -0700
committerJonathan Cameron <Jonathan.Cameron@huawei.com>2018-05-22 18:29:09 +0100
commit96c92d42e9c93b2647d55b84ad883b11baa76307 (patch)
tree75e467f4968fe110479a70d60266b8e296105218 /drivers/iio
parent9ff1d5009fc4b47ac0e6d7818dac0158e1804c3e (diff)
downloadop-kernel-dev-96c92d42e9c93b2647d55b84ad883b11baa76307.zip
op-kernel-dev-96c92d42e9c93b2647d55b84ad883b11baa76307.tar.gz
iio: imu: inv_mpu6050: add comment about frequencies
Although the driver allows frequencies between 4 and 1000 Hz, only the frequencies advertised in the available frequencies file are backed properly by a low-pass filter to prevent aliasing, so it's best to use them. Since this is not obvious to the user, add a comment explaining what's going on. Signed-off-by: Martin Kelly <mkelly@xevo.com> Acked-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Diffstat (limited to 'drivers/iio')
-rw-r--r--drivers/iio/imu/inv_mpu6050/inv_mpu_core.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c b/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
index 43fba5f..f9c0624 100644
--- a/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
+++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
@@ -798,7 +798,14 @@ static const struct iio_chan_spec inv_mpu_channels[] = {
INV_MPU6050_CHAN(IIO_ACCEL, IIO_MOD_Z, INV_MPU6050_SCAN_ACCL_Z),
};
-/* constant IIO attribute */
+/*
+ * The user can choose any frequency between INV_MPU6050_MIN_FIFO_RATE and
+ * INV_MPU6050_MAX_FIFO_RATE, but only these frequencies are matched by the
+ * low-pass filter. Specifically, each of these sampling rates are about twice
+ * the bandwidth of a corresponding low-pass filter, which should eliminate
+ * aliasing following the Nyquist principle. By picking a frequency different
+ * from these, the user risks aliasing effects.
+ */
static IIO_CONST_ATTR_SAMP_FREQ_AVAIL("10 20 50 100 200 500");
static IIO_CONST_ATTR(in_anglvel_scale_available,
"0.000133090 0.000266181 0.000532362 0.001064724");
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