Re: IIO_CONST_ATTR_SCAN_EL_TYPE add result shift?

[Jonathan Cameron <jic23@cam.ac.uk>]

On 10/05/10 13:06, Hennerich, Michael wrote:
> Jonathan Cameron wrote on 2010-10-05:
>> On 10/05/10 12:52, Hennerich, Michael wrote:
>>> Jonathan Cameron wrote on 2010-10-05:
>>>> On 10/05/10 12:24, Hennerich, Michael wrote:
>>>>> /**
>>>>>  * IIO_CONST_ATTR_SCAN_EL_TYPE - attr to specify the data format
>>>>> of a  scan el * @name: the scan el name (may be more general and
>>>>> cover a set  of scan elements * @_sign: either s or u for signed
>>>>> or unsigned *
>>>>>  @_bits: number of actual bits occuplied by the value *
>>>>>  @_storagebits: number of bits _bits is padded to when read out of
>>>>>  buffer  **/
>>>>> #define IIO_CONST_ATTR_SCAN_EL_TYPE(_name, _sign, _bits,
>>>>> _storagebits) \
>>>>>         IIO_CONST_ATTR(_name##_type,
>>>>> #_sign#_bits"/"#_storagebits); There are cases where bits <
>>>>> storagebits and the result is not alligned to the LSB. Lets say we
>>>>> have an 10-bit ADC. The output is stored in a 16-bit word, with
>>>>> four leading zeros, then the 10-bit datum, followed by 2 don't care bits.
>>>>>
>>>>> So it would be good to provide an additional shift value?
>>>>> Or how shall we handle these cases?
>>>> This was discussed in the original debate and we simply proposed
>>>> leaving it until we had a user.  So the question is how to describe
>>>> the shift.
>>>>
>>>> So taking your example, how about:
>>>>
>>>> u10/16>>2
>>>>
>>>> Where the shift is optional.
>>>>
>>>> Other suggestions welcome given I made that up with 2 seconds
>> thought.
>>>
>>> I think this is sufficient. I can only think about right shifts being
>>> useful. This notation would consistently allow both, that's why I like
>>> it. It would be decidedly odd for right shift to make sense.
>>>
>>> A bit off topic - some common defines for signed/unsigned types might
>>> also be useful.
>>>
>>> #define IIO_SCAN_EL_TYPE_SIGNED         's' #define
>>> IIO_SCAN_EL_TYPE_UNSIGNED       'u' Fine with me.
> 
> Shall we add the shift option to the existing macro?
> Or shall we create a new one? How would you name it?
Create a new one (as this is optional and as of yet, not that common)
IIO_CONST_ATTR_SCAN_EL_TYPE_WITH_SHIFT should do the job.


> 
> Greetings,
> Michael
> 
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