Re: ROHM ALS, integration time

[Matti Vaittinen <mazziesaccount@gmail.com>]

On 2/26/23 19:30, Jonathan Cameron wrote:
> On Sat, 18 Feb 2023 20:08:10 +0200
> Matti Vaittinen <mazziesaccount@gmail.com> wrote:
> 
>> Thanks a lot Jonathan,
>>
>> You have been super helpful :) Thanks!
>>
>> On 2/18/23 19:20, Jonathan Cameron wrote:
> Hmm. There is another approach that I'd not thought of in this case because
> in my head integration time is more continuous than it is for this part and
> that is to fiddle the _raw values (we do this for oversampling or SAR ADCs
> where things tend to be powers of 2).  The trick is to shift the raw value
> always so that the 'scale' due to (in this case) integration time remains
> constant.  That separates the two controls completely.

Holy cow! That's a neat trick which I didn't think of!

Basically, we could do >> 1 for the data when time is 100 mS, >> 2 when 
200 mS and >> 3 when 400 mS. We would want to use 19-bit channel values 
then.

> However, I'm not sure that makes sense here where the thing we typically
> want to change when scaling due to saturation is integration time.

That's a bit problematic, yes. We could "fool" the user by doing the 
saturation check in driver, and then just returning the max value of all 
19-bits set if the saturation is detected. This, however, would yield 
raw values that are slightly off. OTOH, with max sift of 3 bits that's 
only 7 'raw ticks' - which I hope is acceptable. I hope the user will 
then be switching to shorter integration time and start getting correct 
readings.

It's slightly sad to say "good bye" to the gain-time-scale helpers but I 
guess you just helped me to solve this with a _really_ simple way. We 
can keep those helpers in "back pocket" for the day when we need them ;)

I will see what comes out of this idea - thanks for the help again!

> 
> Jonathan
>>
>> Yours,
>> 	-- Matti
>>
> 

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

~~ When things go utterly wrong vim users can always type :help! ~~