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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