Hi Matti,
On Mon, Oct 24, 2022 at 6:10 PM Matti Vaittinen
<mazziesaccount@xxxxxxxxx> wrote:
>
> KX022A is a 3-axis accelerometer from ROHM/Kionix. The sensor features
> include variable ODRs, I2C and SPI control, FIFO/LIFO with watermark IRQ,
> tap/motion detection, wake-up & back-to-sleep events, four acceleration
> ranges (2, 4, 8 and 16g), and probably some other cool features.
This is a nice driver, and I found it very helpful as a reference.
One question regarding scale please see below.
> + * range is typically +-2G/4G/8G/16G, distributed over the amount of bits.
> + * The scale table can be calculated using
> + * (range / 2^bits) * g = (range / 2^bits) * 9.80665 m/s^2
> + * => KX022A uses 16 bit (HiRes mode - assume the low 8 bits are zeroed
> + * in low-power mode(?) )
> + * => +/-2G => 4 / 2^16 * 9,80665 * 10^6 (to scale to micro)
> + * => +/-2G - 598.550415
> + * +/-4G - 1197.10083
> + * +/-8G - 2394.20166
> + * +/-16G - 4788.40332
> + */
> +static const int kx022a_scale_table[][2] = {
> + { 598, 550415 },
> + { 1197, 100830 },
> + { 2394, 201660 },
> + { 4788, 403320 },
> +};
Given that the integer part is non-zero, and
IIO_VAL_INT_PLUS_MICRO is returned for read_scale,
As raw value will never be fractional how does this
correspond to a reading of 9.8 m/s² for the Z-axis?
> +
> +static int kx022a_read_avail(struct iio_dev *indio_dev,
> + struct iio_chan_spec const *chan,
> + const int **vals, int *type, int *length,
> + long mask)
> +{
> + switch (mask) {
> + case IIO_CHAN_INFO_SAMP_FREQ:
> + *vals = (const int *)kx022a_accel_samp_freq_table;
> + *length = ARRAY_SIZE(kx022a_accel_samp_freq_table) *
> + ARRAY_SIZE(kx022a_accel_samp_freq_table[0]);
> + *type = IIO_VAL_INT_PLUS_MICRO;
> + return IIO_AVAIL_LIST;
> + case IIO_CHAN_INFO_SCALE:
> + *vals = (const int *)kx022a_scale_table;
> + *length = ARRAY_SIZE(kx022a_scale_table) *
> + ARRAY_SIZE(kx022a_scale_table[0]);
> + *type = IIO_VAL_INT_PLUS_MICRO;
> + return IIO_AVAIL_LIST;
> + default:
> + return -EINVAL;
> + }
> +}
Regards
Jagath
