Re: [PATCH] iio: imu: inv_mpu6050: advertise max and min freqs

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On 05/16/2018 12:51 AM, Jean-Baptiste Maneyrol wrote:


On 15/05/2018 23:53, Martin Kelly wrote:
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Currently, we allow a minimum FIFO rate of 4 and a max of 1000, but we
advertise down to only 10 and up to 1000. Expand the advertised range to
reflect the full available range.

Signed-off-by: Martin Kelly <mkelly@xxxxxxxx>
---
  drivers/iio/imu/inv_mpu6050/inv_mpu_core.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c b/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
index 43fba5f7532b..3f4862f09db3 100644
--- a/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
+++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
@@ -799,7 +799,7 @@ static const struct iio_chan_spec inv_mpu_channels[] = {
  };

  /* constant IIO attribute */
-static IIO_CONST_ATTR_SAMP_FREQ_AVAIL("10 20 50 100 200 500");
+static IIO_CONST_ATTR_SAMP_FREQ_AVAIL("4 10 20 50 100 200 500 1000");
  static IIO_CONST_ATTR(in_anglvel_scale_available,
                                           "0.000133090 0.000266181 0.000532362 0.001064724");
  static IIO_CONST_ATTR(in_accel_scale_available,
--
2.11.0


Hello,

in fact we advertise only frequencies that are supported by the low-pass filter. Filter bandwidths are: 5Hz, 10Hz, 20Hz, 42Hz (~50), 98Hz (~100), 188Hz (~200), which are corresponding to a sampling rate of (x2): 10Hz, 20Hz, ~50Hz, ~200Hz, ~400Hz. Only 500Hz is a little out of specs, since 400Hz is not a possible frequency.

You can always set the frequency to any supported values, but you can suffer from aliasing.

I strongly suggest we just keep it like it is today. Better not advertise frequencies that are not correctly filtered.

JB

OK, that makes sense and is fine with me. Perhaps I should instead just add a comment explaining the situation, since I couldn't tell from the code itself.
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