Re: Why is only one int returned in iio_read_channel_processed?

[Lars-Peter Clausen <lars@metafoo.de>]

On 05/22/2013 03:29 PM, Guillaume Ballet wrote:
> On Wed, May 22, 2013 at 1:43 PM, Lars-Peter Clausen <lars@metafoo.de> wrote:
>> On 05/22/2013 11:37 AM, Guillaume Ballet wrote:
>>>>>
>>>>>>
>>>>>>> functions' signature only has one integer
>>>>>>> in/out parameter. That makes sense in the context of _raw because the
>>>>>>> value isn't yet processed.
>>>>>>>
>>>>>>> However, as the scale is a number encoded over two ints, the
>>>>>>> _processed value should also span two ints. Is there a reason why it's
>>>>>>> still only one int?
>>>>>>
>>>>>> No it certainly should not be one int for exactly the reasons you have
>>>>>> stated.
>>>>>>>
>>>>>>>
>>>>>
>>>>> I'm not to sure about that. I'd rather add a scale parameter to the
>>>>> iio_read_channel_processed, just in the same way the
>>>>> convert_raw_to_processed function takes a scale parameter.
>>>>
>>>> That may be tricky to do given we often have nasty non linear functions
>>>> that are the reason we are using processed in the first place.  Hmm.
>>>> Not sure which way works better.
>>>
>>> I agree, this is the whole point of using processed. Lars, is there a
>>> specific reason why you want to keep reading the value and the scale
>>> in different function calls?
>>
>> I don't want to keep reading scale and value in different function calls.
>>
>> What's you use case and how do you want to split the data between the two
>> integers?
> 
> Since the scale's format can be IIO_VAL_INT_PLUS_MICRO and
> IIO_VAL_INT_PLUS_NANO, etc... and since iio_read_channel_processed
> returns a value that is homogeneous to (value * scale), it seems to me
> the same format should be used as when calling iio_read_channel_raw
> with IIO_CHAN_INFO_SCALE. My use case is not more complicated than
> making sure I keep the same precision when getting processed values.

That doesn't really help me understand what you are trying to do. What is
your application, where do you call iio_read_channel_processed and how do
you process the returned value.

- Lars