On Fri, Aug 25, 2017 at 4:15 AM, Tim Small <[email protected]> wrote: > Since the Beaglebone Black RTC is not usable (I believe due to a hw bug), > I'm using an external RTC chip (A Maxim / Dallas DS1338 on i2c2 at address > 0x68), and informing the kernel about this using a device tree overlay.
Correct, without a battery it's pretty useless. ;) > > I'm also disabling the onboard RTC using a (currently separate) device tree > overlay, this is because otherwise the omap rtc gets enumerated first which > leaves the kernel time starting at jan 1st 2000 on cold boot. The onboard > rtc ends up being /dev/rtc0 (which is linked to by /dev/rtc) and ntpd does > its clock drift adjustment vs this rtc-with-no-battery-backup etc. - it > seemed best to just disable it, since I have another one which is actually > battery-backed. > > This seem to work, but I wanted to check that there wasn't some other > functionality I'd be harming by doing this? > > If anyone is familiar with device tree overlays, I would also appreciate a > review of these: Your overlays look good, have you tried combining them into one file? If it works fine as one file (BB-I2C2-DS1388-00A0.dts) , can you submit a pull request for: https://github.com/beagleboard/bb.org-overlays/tree/master/src/arm and i'll push it out for all users. ;) Regards, > > Firstly BB-DS1388-I2C2-68.dts - which I compile with: > > dtc -W no-unit_address_vs_reg -@ -I dts -O dtb -o > BB-DS1388-I2C2-68-00A0.dtbo BB-DS1388-I2C2-68.dts > > /dts-v1/; > /plugin/; > > / { > > compatible = "ti,beaglebone", "ti,beaglebone-black"; > part-number = "BB-DS1388-I2C2-68"; > version = "00A0"; > > fragment@0 { > target = <&i2c2>; > > __overlay__ { > #address-cells = <1>; > #size-cells = <0>; > pinctrl-0 = <&i2c2_pins>; > > clock-frequency = <100000>; > status = "okay"; > > capertc: rtc@68 { /* Real time clock defined as a child of the i2c2 bus > */ > compatible = "maxim,ds1338"; > #address-cells = <1>; > #size-cells = <0>; > reg = <0x68>; > }; > }; > }; > }; > > > > > Secondly to disable the onboard RTC - BB-NO-OMAP-RTC.dts > > dtc -W no-unit_address_vs_reg -@ -I dts -O dtb -o BB-NO-OMAP-RTC-00A0.dtbo > BB-NO-OMAP-RTC.dts > > /dts-v1/; > /plugin/; > > / { > > compatible = "ti,beaglebone", "ti,beaglebone-black"; > part-number = "BB-NO-OMAP-RTC"; > version = "00A0"; > > fragment@0 { > target = <&rtc>; > > __overlay__ { > status = "disabled"; > > }; > }; > }; > > > Any feedback welcome! > > > Thanks, > > Tim. > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/7ef68dd1-e7c5-49f5-9e4d-32ea021c336b%40googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- Robert Nelson https://rcn-ee.com/ -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/CAOCHtYhsEpD5P6RZXCCUSFjt2iK%3DQ3dxd%3D-NvPREnQM4fZzq1Q%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
