Date: Tue, 26 Nov 2019 15:41:10 -0700 From: Ian Lepore <ian@freebsd.org> To: Stefan Parvu <sparvu@kronometrix.org> Cc: "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org> Subject: Re: rpi3 clock drift Message-ID: <84328c3ce2cf3cc73ff4f54a466f70c3bdd3b759.camel@freebsd.org> In-Reply-To: <702EA0B2-5EA4-41C9-8E8A-D6A2BF634465@kronometrix.org> References: <MWHPR06MB3134CD05551D36CC3B45D368AA450@MWHPR06MB3134.namprd06.prod.outlook.com> <702EA0B2-5EA4-41C9-8E8A-D6A2BF634465@kronometrix.org>
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On Wed, 2019-11-27 at 00:18 +0200, Stefan Parvu wrote: > > I was thinking of ordering an I2C RTC but I'm unsure how to make > > FreeBSD aware of the clock. > > We are currently using and heavily testing this RTC: > https://afterthoughtsoftware.com/products/rasclock > > based on NXP PCF2129. See here complete description of a product > based on FreeBSD 12 and RPI3+ > https://kronometrix.com/wp-content/uploads/2019/11/Kronometrix-K1.pdf > > > Follow this thread for more instructions and hints how to get this > RTC working with FreeBSD 12. > http://freebsd.1045724.x6.nabble.com/Rasclock-PCF2127-Hardware-Clock-FreeBSD-12-0-td6339218.html > > I don't see that I ever followed up in that thread about the rasclock, but I eventually updated the driver to init the chip into a lower power mode and basically doubled the running-on-battery lifetime (cut the power draw in half). I also added a sysctl that lets you set the chip's oscillator drift tuning, and I found that by doing so you could reduce the drift to about 1ppm (which is damn good for a cheap crystal rtc). You can just grab the code from the driver on head and recompile it on whichever branch you're using to get those features. -- Ian
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