>-----Original Message-----
>From: Xenomai <[email protected]> On Behalf Of Prasanna Kannan via
>Xenomai
>Sent: Friday, May 27, 2022 9:39 PM
>To: [email protected]
>Subject: Difference between Xenomai timer and Linux clock
>
>Hello Everybody,
>
>I am comparing the Xenomai Timer(rt_timer_read()) and clock_gettime() with
>CLOCK_REALTIME and found that the two drift at roughly 100 us/s
>Here is the snippet from my code:
>
>init():
>clock_gettime(CLOCK_REALTIME, &ts_start);
>rtime_start = rt_timer_read();
>
>runtime():
>clk_xenotime = (rt_timer_read() - rtime_start) * 1e-9;
>clock_gettime(CLOCK_REALTIME, &ts);
>clk_rttime = (ts.tv_sec - ts_start.tv_sec) + (ts.tv_nsec -
>ts_start.tv_nsec) * 1e-9;
>delta = clk_rttime - clk_xenotime
>
>The observation is that the delta is around 100us/s
>...
>ClockGetTime:2.588435s, rt_timer_read:2.588167s, delta:0.000268s
>ClockGetTime:3.588533s, rt_timer_read:3.588161s, delta:0.000372s
>ClockGetTime:4.588671s, rt_timer_read:4.588196s, delta:0.000475s
>...
>
>The Linux clock is not corrected via NTP/PTP, thus I am wondering why they
>are drifting in this way.
>
>Some Information about my setup:
>Xenomai/cobalt v3.1
>Linux rtdonau 4.19.115-ipipe #54 SMP PREEMPT Wed Oct 13 12:16:56 CEST 2021
>x86_64 GNU/Linux
>Kernel parameters: intel_idle.max_cstate=0 vga=0x317 ip=dhcp root=/dev/nfs
>nfsroot=10.0.0.1:/opt/xyz/xeno_rt,tcp,nfsvers=3 BOOT_IMAGE=xeno10.2
>I-pipe release #12 detected
>Cobalt core 3.1 detected
>Compiler: gcc version 7.5.0 (GCC)
>Build args: --prefix=/opt/xenomai-3.1 --enable-smp --enable-pshared
>--enable-dlopen-libs
>
>The hardware used is an Intel SBC based on Core i7-4700EQ CPU @ 2.40GHz
One of what we found is that there is delayed work which would refine tsc clock
after Xenomai init and that cause
Clock difference which may result in such drift. The patchset "[Cobalt
Xenoami3.1 PATCH 0/2] notify Xenomai udpated clockfreq."
I sent in community at 5/27 try to fix what we found. Could you send your
complete linux dmsg to check if our issues is the same?
Regards
Hongzhan Chen
>
>Thank you in Advance.
>
>Best Regards
>Prasanna
>
