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

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Date:	Thu, 23 Aug 2012 11:15:09 +0000
From:	"AnilKumar, Chimata" <anilkumar@...com>
To:	Chinmay V S <cvs268@...il.com>
CC:	"carmine.iascone@...com" <carmine.iascone@...com>,
	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

Chinmay,

On Thu, Aug 23, 2012 at 15:53:10, Chinmay V S wrote:
> > Note from datasheet, "1LSb=4g/4096 at 12bit representation,
> > ±2g Full-scale"
> 
> Precisely my point. All the datasheet says is :
> 1. It is +/-2G mode --> so Numerator is 4G.
> 2. We are using 12bits --> so Denominator is 2^12 = 4096.
> 
> There is no clear reason/justification as to why 12bits was chosen in
> the first place. At this point unless someone from the
> design/original-driver team actually confirms why the 12bit
> representation was chosen, it is all conjecture on our part.
> 
> If you have the actual LIS331DLH hardware, can you verify if the lower
> 4bits do actually contain any data (or are they always zero). This
> will help us decide whether to use them(16bit mode) or discard
> them(12bit mode)?...
> 

This is the outdata of accelerometer

root@...35xevm:~# cat /sys/devices/platform/lis3lv02d/position
[   16.323852] lis3lv02d: hi 0x1    low 0x50   val 0x15
[   16.329742] lis3lv02d: hi 0x0    low 0x0    val 0x0
[   16.335052] lis3lv02d: hi 0x3e   low 0x50   val 0x3e5
(20,0,973)
root@...35xevm:~# cat /sys/devices/platform/lis3lv02d/position
[   25.777343] lis3lv02d: hi 0x2    low 0xa0   val 0x2a
[   25.783203] lis3lv02d: hi 0xc1   low 0xf0   val 0xfffffc1f
[   25.790130] lis3lv02d: hi 0xfd   low 0x50   val 0xffffffd5
(41,-969,-41)
root@...35xevm:~# cat /sys/devices/platform/lis3lv02d/position
[   47.607330] lis3lv02d: hi 0xc0   low 0x60   val 0xfffffc06
[   47.613464] lis3lv02d: hi 0xfd   low 0x90   val 0xffffffd9
[   47.619934] lis3lv02d: hi 0x2    low 0x40   val 0x24
(-994,-38,35)

Lower nibble always "0"

Regards
AnilKumar
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