On Fri, Apr 17, 2020 at 01:40:18PM +0200, Linus Walleij wrote:
> The original AK8974 has 16 bits of actual value, while the
> HSCDTD008A has 15 bits and the AMI305 and AMI306 has 12 bits.
> Correct this by providing an extra parameter to the channel
> macro and define a separate set of channels for each variant
> of the chip. The resolution is the actual resolution of the
> internal ADC of the chip.
>
> The values are stored in a S16 in 2's complement so all 16
> bits are used for storing (no shifting needed).
>
> The AMI305, AMI306 and HSCDTD008A valid bits are picked from
> respective datasheet.
>
> My best educated guess is that AK8974 is also 12 bits. The
> AK8973 is an 8 bit and earlier version, and the sibling
> drivers AMI305 and AMI306 are 12 bits, so it makes sense
> to assume that the AK8974 is also 12 bits.
[...]
> -#define AK8974_AXIS_CHANNEL(axis, index) \
> +#define AK8974_AXIS_CHANNEL(axis, index, bits) \
> { \
> .type = IIO_MAGN, \
> .modified = 1, \
> @@ -662,16 +662,42 @@ static const struct iio_chan_spec_ext_info ak8974_ext_info[] = {
> .scan_index = index, \
> .scan_type = { \
> .sign = 's', \
> - .realbits = 16, \
> + .realbits = bits, \
> .storagebits = 16, \
> .endianness = IIO_LE \
> }, \
> }
>
> +/*
> + * We have no datasheet for the AK8974 but we guess that its
> + * ADC is 12 bits.
> + */
> static const struct iio_chan_spec ak8974_channels[] = {
> - AK8974_AXIS_CHANNEL(X, 0),
> - AK8974_AXIS_CHANNEL(Y, 1),
> - AK8974_AXIS_CHANNEL(Z, 2),
> + AK8974_AXIS_CHANNEL(X, 0, 12),
> + AK8974_AXIS_CHANNEL(Y, 1, 12),
> + AK8974_AXIS_CHANNEL(Z, 2, 12),
> + IIO_CHAN_SOFT_TIMESTAMP(3),
> +};
> +
> +/*
> + * The AMI305 and AMI306 have 12 bit ADC resolution according to
> + * datasheets.
> + */
> +static const struct iio_chan_spec ami30x_channels[] = {
> + AK8974_AXIS_CHANNEL(X, 0, 12),
> + AK8974_AXIS_CHANNEL(Y, 1, 12),
> + AK8974_AXIS_CHANNEL(Z, 2, 12),
> + IIO_CHAN_SOFT_TIMESTAMP(3),
> +};
Maybe call it channels_12bit[] and then you wouldn't need to make
am exact duplicate for ak8974?
Best Regards,
Michał Mirosław
