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

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Message-ID: <331ABD5ECB02734CA317220B2BBEABC13EA1BDA9@DBDE01.ent.ti.com>
Date:	Wed, 22 Aug 2012 15:40:25 +0000
From:	"AnilKumar, Chimata" <anilkumar@...com>
To:	Chinmay V S <cvs268@...il.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 16:09:22, Chinmay V S wrote:
> Hmmm. Interesting. As i understand LIS331DLH provides 16bit data
> irrespective of the full-scale/sensitivity configuration. Hence we
> could effectively map +/-2G to +/-32768(signed 16bit 2's complement).
> According to the current-patch right-shifting the register values by
> 4(i.e. reducing 16bit --> 12bit) will mean that we lose accuracy by
> ~1mG.
> 
> Clearly this will NOT affect use-case like display-orientation in
> smart-phones, but surely medical and industrial applications WILL
> benefit from the additional accuracy by utilising the entire 16-bit
> resolution provided by LIS331DLH hardware.
> 
> I went through the LIS331DLH datasheet/application-note from
> http://www.st.com/internet/analog/product/218132.jsp and i'm a bit
> confused from your statement about +/-2G being 12bit data. Nowhere is
> it mentioned that LIS331DLH provides +/-2G|+/-4G|+/-8G as 12|13|14 bit
> data respectively. Then again i might be wrong...
> 

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

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.

Thanks
AnilKumar
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