linux-kernel - RE: [PATCH 4/5] max17042: Fix value scaling for VCELL and avgVCELL

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Date:	Tue, 13 Mar 2012 17:04:25 -0700
From:	Jason Wortham <Jason.Wortham@...im-ic.com>
To:	Dirk Brandewie <dirk.brandewie@...il.com>
CC:	bruce robertson <bruce.e.robertson@...el.com>,
	Anton Vorontsov <cbouatmailru@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dg77.kim@...sung.com" <dg77.kim@...sung.com>,
	"kyungmin.park@...sung.com" <kyungmin.park@...sung.com>,
	"myungjoo.ham@...sung.com" <myungjoo.ham@...sung.com>
Subject: RE: [PATCH 4/5] max17042: Fix value scaling for VCELL and avgVCELL

Ok, the datasheet is written that way as a commitment about the hardware ADC accuracy/resolution.  However, the ADC performs a set of 8x samples, and as a result will have an average which provides some additional "fake" resolution.  Even though this extra resolution isn't strong in an analog way, it's still useful information.

But I guess I'm really splitting hairs here since it's such a small resolution.

--Jason

-----Original Message-----
From: Dirk Brandewie [mailto:dirk.brandewie@...il.com] 
Sent: Tuesday, March 13, 2012 3:59 PM
To: Jason Wortham
Cc: bruce robertson; Anton Vorontsov; dirk.brandewie@...il.com; linux-kernel@...r.kernel.org; dg77.kim@...sung.com; kyungmin.park@...sung.com; myungjoo.ham@...sung.com
Subject: Re: [PATCH 4/5] max17042: Fix value scaling for VCELL and avgVCELL

On 03/13/2012 02:04 PM, Jason Wortham wrote:
> The bottom 3 bits are still functional bits and aren't required to be masked.  Arguably these bits are below the hardware accuracy of the ADC, however, they still provide some averaging information.
>

The datasheet for the 17042 shows the bottom three bits as don't care that
was the reason for the mask.

If Jason says it is still accurate without the mask I am fine with it.

--Dirk
> --Jason
>
> -----Original Message-----
> From: bruce robertson [mailto:bruce.e.robertson@...el.com]
> Sent: Tuesday, March 13, 2012 2:00 PM
> To: Anton Vorontsov
> Cc: dirk.brandewie@...il.com; linux-kernel@...r.kernel.org; dg77.kim@...sung.com; kyungmin.park@...sung.com; myungjoo.ham@...sung.com; Jason Wortham
> Subject: Re: [PATCH 4/5] max17042: Fix value scaling for VCELL and avgVCELL
>
> Anton Vorontsov<cbouatmailru@...il.com>  writes:
>
>> On Tue, Jan 24, 2012 at 09:26:07AM -0800, dirk.brandewie@...il.com wrote:
>>> From: Bruce Robertson<bruce.e.robertson@...el.com>
>>>
>>> The bottom three bits of the register are don't care bits.  The LSB
>>> value is 625 uV.  Adjust the returned values appropriately
>>>
>>> Signed-off-by: Bruce Robertson<bruce.e.robertson@...el.com>
>>> Signed-off-by: Dirk Brandewie<dirk.brandewie@...il.com>
>>> Acked-by: MyungJoo Ham<myungjoo.ham@...sung.com>
>>
>> I guess this was fixed long ago by the following patch:
>>
>> commit cf7a8c03db792894f436db5f3ffc44d947b9b068
>> Author: MyungJoo Ham<myungjoo.ham@...sung.com>
>> Date:   Wed Aug 17 10:18:34 2011 +0900
>>
>>      max17042_battery: Bugfix of incorrect voltage register value interpretation
>>
>>      The calculation had error in getting voltage values from
>>      MAX17042 registers. The least bit denotes 78.125uV (625/8).
>
> The multipliers I see in the patch are 83 making the voltages somewhat
> high and the low 3 bits are not masked off. I'm probably misreading the code.
>
>>
>>      Signed-off-by: MyungJoo Ham<myungjoo.ham@...sung.com>
>>      Signed-off-by: Philip Rakity<prakity@...vell.com>
>>      Signed-off-by: Kyungmin Park<kyungmin.park@...sung.com>
>>      Signed-off-by: Anton Vorontsov<cbouatmailru@...il.com>
>>
>> Thanks,

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