Date: Mon, 23 May 2016 12:32:31 -0700 From: Ravi Pokala <rpokala@mac.com> To: Warner Losh <imp@bsdimp.com>, Justin Hibbits <chmeeedalf@gmail.com> Cc: src-committers <src-committers@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, Luiz Otavio O Souza <loos@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@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 Message-ID: <F5C36C53-1125-4109-9296-513C4E66660A@panasas.com> In-Reply-To: <CANCZdfpsEpgb_B2mbiZqFGuwOb-rcDxf5KJLaEcavw7mD%2BHj0g@mail.gmail.com> References: <201605221358.u4MDwW8u097510@repo.freebsd.org> <C66E915D-A4D7-4591-AF6C-0949AF184271@panasas.com> <CAHSQbTAVt6QgVNz0M_yCVpTwSc=-YFU5O0uhaqKC6XOPOmJCkQ@mail.gmail.com> <CANCZdfpsEpgb_B2mbiZqFGuwOb-rcDxf5KJLaEcavw7mD%2BHj0g@mail.gmail.com>
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-----Original Message----- From: <owner-src-committers@freebsd.org> on behalf of Warner Losh <imp@bsdimp.com> Date: 2016-05-23, Monday at 10:37 To: Justin Hibbits <chmeeedalf@gmail.com> Cc: Ravi Pokala <rpokala@mac.com>, src-committers <src-committers@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, Luiz Otavio O Souza <loos@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@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@gmail.com> wrote: >> >> On May 22, 2016 13:51, "Ravi Pokala" <rpokala@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
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