Re: [PATCH] IIO: ADC: New driver for AD7792/AD7793 3 Channel SPI ADC

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

On 05/27/11 11:23, Michael Hennerich wrote:
> On 05/27/2011 11:44 AM, Jonathan Cameron wrote:
>> ...
>>> Hi Jonathan,
>>>
>>>
>>> root:/sys/devices/platform/bfin-spi.0/spi0.18/device0>  ls
>>> device0:buffer0               power
>>> in-in_scale                   range
>>> in0-in0_raw                   range_available
>>> in1-in1_raw                   sampling_frequency
>>> in2-in2_raw                   sampling_frequency_available
>>> in3_raw                       subsystem
>>> in4_supply_raw                temp0_raw
>>> in4_supply_scale              temp_scale
>>> in_scale                      trigger
>>> name                          uevent
>>>
>>> root:/sys/devices/platform/bfin-spi.0/spi0.18/device0>  cat in_scale
>>> 0.000140
>>>
>>> root:/sys/devices/platform/bfin-spi.0/spi0.18/device0>  cat range_available
>>> 2500 1250 625 312 156 78 39 19
>>>
>>> root:/sys/devices/platform/bfin-spi.0/spi0.18/device0>  echo 312>  range
>>> root:/sys/devices/platform/bfin-spi.0/spi0.18/device0>  cat in_scale
>>> 0.000010
>>>
>>> root:/sys/devices/platform/bfin-spi.0/spi0.18/device0>  echo 78>  range
>>> root:/sys/devices/platform/bfin-spi.0/spi0.18/device0>  cat in_scale
>>> 0.000000
>>> root:/sys/devices/platform/bfin-spi.0/spi0.18/device0>
>>>
>>> with these 24-bit converters and input AMPs we are already exhausted
>>> the number of available digits we have for scale.
>> Time for a new return type and extra logic in the core.
>> IIO_VAL_INT_PLUS_NANO
>>
>> should still fit in a 32 bit long.  Perhaps it's better to make a  bigger jump - or
>> this will just bite us again sometime soon.
>>
>> After nano we will have to start having padding zeros which is going to be a little
>> strange - or I guess we don't have to keep val as being int...
>>
>> IIO_VAL_MICRO_PLUS_PICO maybe?  The maximum option of IIO_VAL_NANO_PLUS_ATTO seems a little
>> 'odd'.
>>
>> The more complex question is going to be writing values that are this small. I think we will
>> have to add another callback into the drivers where they can query what format a value should
>> be in so the core can provide it.  Make this optional so it doesn't effect the majority
>> of drivers where int + micro does the job.
>>
> IIO_VAL_INT_PLUS_NANO should do the job for now.
> 
>>> What shall we do?
>>>
>>> Also how would you name AIN1(-) - AIN1(-)?
>>>
>>> #define AD7793_CH_AIN1P_AIN1M        0 /* AIN1(+) - AIN1(-) */
>>> #define AD7793_CH_AIN2P_AIN2M        1 /* AIN2(+) - AIN2(-) */
>>> #define AD7793_CH_AIN3P_AIN3M        2 /* AIN3(+) - AIN3(-) */
>>> #define AD7793_CH_AIN1M_AIN1M        3 /* AIN1(-) - AIN1(-) */
>>>
>>> in0-in0_zerooffset_raw ?
>> Hmm.. That is awkward.  Given only the channel numbers exist in event codes
>> it will also possibly cause us issues at some later date.
>> How about having in0-in0_raw then in0-in0_offset + in0-in0_offset_available.
>> (actually this would be shared I guess so in-in_offset_available).
>> A little clunky, but does fit better within the api.  Is there a real use case
>> for buffering where one grabs both offsets in the same scan?
> As far as I understand things - We do zero and full scale calibration,
> The results read from the other channels should have the offset eliminated.
> I agree the offset read from  AIN1(-) - AIN1(-) should be the same for all channels.
> So in-in_offset sounds good to me - why _available?
Because there are two options possible.  One when we are doing signed output
and one for differential but with only positive values possible.
>> Jonathan
>>
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> 
>