[etherlab-users] [PATNI] Regarding DC Synchronisation

[Andreas Stewering-Bone]

Hello Yogesh,

you have to notice following steps:

- If you want to do DC, you have to use a RT-kernel and a 
RT-application, because jitter on the base system can be a sync problem.

- Do not use NTP on the system, use CLOCK_MONOTONIC or 
CLOCK_MONOTONIC_RAW if accessible to get a stable clocksource.

- Get system time just before you set the application time, to get the 
correct time.

- Sync slaves every transmit cycle.

- Rise up the cycle freq, the DC syncs better if you have faster 
transmit cycles

- your  second question: see doc under page 27- >  watch -n0 "ethercat 
reg read -p4 -tsm32 0x92c"



Best regards

Andreas

Am 19.05.2011 08:59, schrieb Dhake, Yogesh:
>
> Hi,
>
> EtherCAT master performs DC synchronization as below:
>
> 1) Initially EtherCAT master calculates Propagation delay time between 
> slaves.
>
> 2) Time Delay calculated (actual frame send from Master state machine 
> - application start time) and deducted from System Time read from 
> slave. New Offset time (new offset = old offset from slave + time 
> difference between Master Application Start Time and Slave System 
> Time) is send to slaves.
>
> 3) After this, Master sends synchronization datagram (with command 
> FRMW-First READ MULTIPLE WRITE) to reference clock slave as well as to 
> other EtherCAT slaves on network.
>
> 4) FRMW command reads reference clock slave system time (lower 32 bit) 
> (0x0910 to 0x0927) and writes to lower 32 bit of other EtherCAT slave 
> system time register (0x0910 to 0x0927).
>
> 5) Activity number 2 to 4 happens at every 10ms in user application.
>
> 6) Our observation is difference between master time and slave system 
> time is around 16-20 seconds after step 2.
>
> 7) Slave System Time is not accessible to us for checking whether 
> Slave System Time synchronized with Master Application Time.
>
> Our query is:
>
> 1. How can we reduce difference between Master Application Time and 
> Slave System Time in step 2?
>
> 2. How to check System Time register of BECKHOFF slave after step 4?
>
> Please let us know your valuable inputs regarding synchronization of 
> Distributed clocks of EtherCAT slaves.
>
> Please find attached DC synchronization process. Rename file to .png type.
>
> Regards,
>
> Yogesh
>
>
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Mit freundlichem Gruß

Andreas Stewering-Bone

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