svn commit: r300421 - in head/sys: arm/allwinner arm/broadcom/bcm2835 arm/freescale/imx arm/mv dev/acpi_support dev/acpica dev/amdtemp dev/coretemp dev/iicbus powerpc/powermac

[Ravi Pokala]

-----Original Message-----
From: <owner-src-committers at freebsd.org> on behalf of Warner Losh <imp at bsdimp.com>
Date: 2016-05-23, Monday at 10:37
To: Justin Hibbits <chmeeedalf at gmail.com>
Cc: Ravi Pokala <rpokala at mac.com>, src-committers <src-committers at freebsd.org>, "svn-src-head at freebsd.org" <svn-src-head at freebsd.org>, Luiz Otavio O Souza <loos at freebsd.org>, "svn-src-all at freebsd.org" <svn-src-all at freebsd.org>
Subject: Re: svn commit: r300421 - in head/sys: arm/allwinner arm/broadcom/bcm2835 arm/freescale/imx arm/mv dev/acpi_support dev/acpica dev/amdtemp dev/coretemp dev/iicbus powerpc/powermac

>On Sun, May 22, 2016 at 1:12 PM, Justin Hibbits <chmeeedalf at gmail.com> wrote:
>>
>> On May 22, 2016 13:51, "Ravi Pokala" <rpokala at mac.com> wrote:
>>>
>>> Out of morbid curiosity, why do these things report in deciKelvin anyway?
>>> Are there sensors we support out there which report native Kelvin, or that
>>> report sub-degree precision?
>>>
>>> Thanks,
>>>
>>> Ravi (rpokala@)
>>>
>>
>> There are many i2c sensors which report in sub-degree centigrade. Though
>> some of them are in 1/8 (or other power of 2) degree precision, not 1/10.
>
>ACPI reports in decikelvin, and it was the first thing we supported. Some 1 wire
>devices support 1/16th a degree, and we support it in millikelvin since 1/16th
>is 0.0625. So the precision needed is actually greater than what we're
>reporting.
>However, the accuracy of the measurement isn't +/- 0.001, it's closer
>to +/1 0.063
>or so (well, that's a relative accuracy, absolute accuracy is closer
>to +/- 1 degree).
>We report the higher level of precision so that applications that use
>the relative
>temperature can use it to inform a control loop. We have no good way to report
>relative precision for a measurement, or the absolute accuracy.
>
>Warner

Good to know. Thanks guys.

-Ravi