Thanks Jan

We use this setup: Two computers are RTnet-slaves synchronized to provide them common time. These two computers also have a second NIC which tap a target Ethernet network using RTcap. In this way we can measure Ethernet travel times on the target network.

This works well. The only problem is that we don't know exactly how to handle if a TDMA sync arrives at the same time as RTcap captures a frame on the target network.

We ran a test where we only read the system time from kernel space using rt_timer_read(). This reading and saving to a file takes approximately 1 us. However this time increases to approx 16 us when the reading is made when a synchronization TDMA packet is being handled.

We would like to detect when this happens so we can discard the frame travel times that collide with the TDMA sync.

I hope this makes sense

Benjamin

Kiszka wrote:

Benjamin Biegel wrote:

What has highest priority RTcap or TDMA-synchronization reception?

We have a PC with two NICs, so one has TDMA, and one other captures with 
RTcap. If two frames arrive at the same time on both NICS, which is 
handled? Is it the first one, or does one have higher priority than the 
other?

Any help directly or where to look is appreciated.


Timestamping and packet queuing of both sources work at exactly the same
priority and even go through a common path, the Stack Manager task. So
the ordering is more or less random. But the final delivery happens at
different level: TDMA is handled at high RT prio, RTcap captured frames
are forwarded to Linux, thus are then saved at the according low prio.

But why are you running two NICs instead of attaching RTcap to the
TDMA-managed interface? Or are they connected to different Ethernets?

Jan