Re: Variable accuracy devices.

[Michael Hennerich <michael.hennerich@analog.com>]

On 06/28/2011 11:58 AM, Jonathan Cameron wrote:
> Hi All,
>
> There are a couple of different types of variable accuracy drivers in three.
>
> 1) Devices with variable gain - these are well handled
>
> 2) Devices with variable number of bits per sample. Typically they will
>     do higher accuracy at a slower rate.
>
> 3) Variable bit depths in hardware ring buffers (sca3000 only - currently
> glossed over).
>
>
> In case 2 we have for example the adis16130 gyro driver (a very simple driver).
> This one doesn't currently implement buffered capture, so our only read route
> is through the sysfs attributes.   So my question here is whether there is
> a use case for sampling at anything other than maximum accuracy if we are
> reading via a slow path anyway?
I don't think so.
>    Basically I'd like to drop the non standard
> interface that this driver has.
ACK

> Case 3 is one I've been avoiding mainly because it only exists in one driver
> right now and that one is for a long deprecated part.   It is however similar
> to a controllable nbit adc or indeed the adis16130 gyro.  In those cases we
> want to be able to control the accuracy of data that is captured into a
> software buffer.  Right now we don't have an easy way of doing this.
>
> The solution that comes to mind is:
> Additional optional callback within ring_setup_ops (it kind of fits in there
> if we broaden the term setup somewhat), checked by equivalent replacement
> of iio_show_fixed_type.  If it's present, the driver is queried, if not then
> we use the fixed type stuff from the iio_chan_spec structure.  Clearly
> we will also need a write function.  The matching _available attribute
> could be done by a second callback.
>
> What do people think?
Sounds good to me.

-- 
Greetings,
Michael

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