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

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Message-ID: <CAK-9PRDncAn7vBPywr4R+tOiTHtXjLnW35Yysjx3vaFHLUsRWA@mail.gmail.com>
Date:	Thu, 23 Aug 2012 17:03:31 +0530
From:	Chinmay V S <cvs268@...il.com>
To:	"AnilKumar, Chimata" <anilkumar@...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

12bit it IS then. :-)
LGTM. +1.

On Thu, Aug 23, 2012 at 4:45 PM, AnilKumar, Chimata <anilkumar@...com> wrote:
> 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

-- 
regards
ChinmayVS
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