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iio: imu: inv_mpu6050: add comment about frequencies

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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>
This commit is contained in:
Martin Kelly 2018-05-21 11:41:54 -07:00 committed by Jonathan Cameron
parent 9ff1d5009f
commit 96c92d42e9
1 changed files with 8 additions and 1 deletions
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9
drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
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@ -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");