Re: [yocto] connman + busybox-hwclock startup failure

From: Mike Looijmans <mike.looijmans@topic.nl>
To: yocto@lists.yoctoproject.org
Subject: Re: [yocto] connman + busybox-hwclock startup failure
Date: Fri, 28 Jul 2023 08:15:02 +0200	[thread overview]
Message-ID: <90948cc2-b8d4-dd9b-e419-ffa683c273e1@topic.nl> (raw)
In-Reply-To: <CAHkgX0uZ0Hd5aMx+OcGuYnNdjVjY-nGCWLwL-D9-TbsnXo-m6w@mail.gmail.com>

A bit late, but might be useful to others.

The Linux kernel has options to set the RTC time at boot. This will happen as 
soon as the RTC probes, which is often before the rootfs mounts.

The kernel also has an option to synchronize the RTC to NTP time (userspace 
provides the actual NTP) when available.

Combined this completely replaces the hwclock functionality. In fact, I found 
that I had to bbappend the busybox recipeand remove the hwclock scripts, they 
actually interfere with proper operation:
- At boot, the RTC clock is copied twice
- At shutdown the RTC is set. But most RTC clocks have more accurate time 
keeping (e.g. temperature compensated crystal) than what the system has, so 
this usually makes things worse. Better to set the RTC time from userspace and 
leave it alone.
- Most RTCs have only "second" resolution and setting it too often makes it 
drift more.

On 31-03-2023 00:04, Chris Elledge via lists.yoctoproject.org wrote:
> I've encountered an issue when using a system that has both connman and the 
> hwclock.sh script enabled during startup. The default combined startup order 
> for these two services is wrong.
> 
> Currently connman starts at 05, and hwclock.sh is at 20 (default for 
> update-rc.d). This means that we have a situation where connman starts up and 
> obtains a correct NTP time, then hwclock.sh clobbers the system time with 
> whatever is in the RTC even if it is way in the past. The big issue caused by 
> that is connman schedules its next NTP update at an absolute time of (current 
> time + 1024s). Once the hwclock.sh script knocks the system time way into the 
> past, the NTP update will not run for a potentially very long time.
> 
> I would suggest adding a line to poky/meta/recipes-core/busybox.inc to move 
> hwclock.sh earlier.
> For example:
> INITSCRIPT_PARAMS:${PN}-hwclock = "start 04 2 3 4 5 . stop 20 0 1 6"
> or
> INITSCRIPT_PARAMS:${PN}-hwclock = "start 40 S . stop 20 0 1 6"
> 
> Thanks,
> Chris Elledge
> 
> 

-- 
Mike Looijmans
System Expert

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