linux-kernel - RE: [PATCH v2] lis3lv02d: Add STMicroelectronics lis331dlh digital accelerometer

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Date:	Thu, 23 Aug 2012 10:00:54 +0000
From:	"AnilKumar, Chimata" <anilkumar@...com>
To:	Chinmay V S <cvs268@...il.com>,
	"carmine.iascone@...com" <carmine.iascone@...com>
CC:	Arnd Bergmann <arnd@...db.de>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"eric.piel@...mplin-utc.net" <eric.piel@...mplin-utc.net>,
	"jic23@....ac.uk" <jic23@....ac.uk>,
	"greg@...ah.com" <greg@...ah.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"broonie@...nsource.wolfsonmicro.com" 
	<broonie@...nsource.wolfsonmicro.com>,
	"dmitry.torokhov@...il.com" <dmitry.torokhov@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] lis3lv02d: Add STMicroelectronics lis331dlh digital
 accelerometer

On Wed, Aug 22, 2012 at 22:24:10, Chinmay V S wrote:
> > Look at this application note which talks about the outdata values
> > for 2G range (page 12/31) http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/APPLICATION_NOTE/CD00215823.pdf
> 
> Had been through the application note earlier. The table5 (on page 12)
> that you refer to, does NOT contradict either 12/16bit, as in all the
> examples the lower 4 bits are zero. So i don't see how one can assume
> from these examples that for +/-2G they one should consider 12/16bits.
> A nice side-effect of using 12|13|14bits for +/-2|4|8G is that the
> values returned by the driver are in mG in all the 3 modes.
> 
> > Corresponding to the 4G and 8G I got the details form older
> > patches (SHIFT_ADJ_4G and SHIFT_ADJ_8G).
> > http://driverdev.linuxdriverproject.org/pipermail/devel/2010-November/009685.html
> >
> > We can easily interpret number of bits for 4G and 8G from 2G
> > information.
> 
> Going through the code of this driver i can see what you are talking
> about. Depending on the full-scale-range the device is being
> configured for, the number of bits used to represent acceleration in
> the driver is changed.
> 
> Again judging from the code, the driver is always returning
> acceleration at a constant accuracy i.e. 1mG in all the 3 modes
> (+/-2|4|8G)i.e.
> +/-2G is mode means value can be anywhere from +/-2048mG,
> (requiring 12bits.)
> +/-4G in the range of +/-4096mG, requiring 13bits.
> +/-8G i.e. +/-8192mG, requiring 14bits.
> 
> Was this done...
> 
> a. ...because LIS331DLH's theoretical MAX accuracy is ~1mG
> If yes, then using 12bits is fine.
> 

Note from datasheet, "1LSb=4g/4096 at 12bit representation,
±2g Full-scale"

>From this I understood that ±2G full scale value is 12 bits.
That is one more reason to take 12bit value.

Regards
AnilKumar
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