[etherlab-users] rtai_rtdm_dc example, "error: system_time_base less than system time" message

Bilko AS, Oguz Dilmac odilmac at bilko-automation.com
Mon Jan 25 16:37:23 CET 2016


We have been using EtherCAT master 1.5.2 for about two years. We have 
successfully implemented 4 machines. Each has 5 Kollmorgen AKD servo 
drives and some Beckhoff IO modules.
Now we are implementing a new machine. On this machine we usually get 
the following messages:
"system2count() error: system_time_base less than system time 
(system_time_base: -58905492552780, time:680659495658"
"system2count() error: system_time_base less than system time 
(system_time_base: -58905492552858, time:680660495658"
"system2count() error: system_time_base less than system time 
(system_time_base: -58905492552936, time:680661495658"
"system2count() error: system_time_base less than system time 
(system_time_base: -58905492553014, time:680662495658"

We implemented our system based on the *rtai_rtdm_dc* example. Only main 
difference is, we use kernel modules with RTAI instead of LXRT user mod.
We are using "cyclic positon" (8) mode with distributed clock.
We choose the first DC capable device as the reference clock by calling 
*ecrt_master_select_reference_clock(master, 0);
*The first node on the bus is a AKD servo drive.

The error occurs from the startup and not disappear until we reboot the 
PC and the drives.
When the error occurs, it seems sometimes drives can't update the new 
position reference. Therefore, if it is moving, it tries to stop for one 
sample and continues to the new reference at the next sample.
This causes a loud "knock" sound on the machine.

We didn't get this message with previous 4 machines.
We tried different FW versions of the AKD drives. Also tried to change 
the bus node order of the drives. But nothing changed.
Do you know what can be the cause for this message? How can we fix the 

Best regards,


Oguz Dilmac
ARGE Bolumu

Bilko AS, R&D Department
Perpa Ticaret Merkezi B Blok Kat 13 Nr. 2568
TR-34384 Okmeydani Istanbul Turkey
Tel : +90 212 220 07 40  Fax :   +90 212 210 47 01
e-mail : odilmac at bilko-automation.com
web site : http://www.bilko-automation.com

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