Hi, Thanks for you fast reply.
Here are some results:
with a Ethercat task of 4ms and 25% sync offset i get this: Max Cycle Time : 1830 microsec but an unreasonable Jitter Max: 6029 microsec e Min: -3531 microsec
as you can see in the second picture.
Then with an Ethercat task of 8ms and 50% sync offset i get: Max Cycle Time : 1732 microsec but an unreasonable Jitter Max: 6675 microsec e Min: -6685 microsec
as you can see in the first picture.
This Jitter values are likely to be the problem !!!! I've never seen Jitters so high. What can be the problem? I used 2 BBB with the same results.
I use this kernel:
Linux beaglebone 4.4.14-bone-rt-r11 #1 PREEMPT RT Fri Jul 1 01:43:25 UTC 2016 armv7l GNU/Linux
I tried with the OS installed on SD as well on the eMMC.
EDIT: I also tried with a raspberry Pi 2 Model B