To measure performance of the pcap POWERLINK demo while
- IO data is exchanged in the isochronous phase and
- A video is streamed over the asynchronous phase
The video demonstration shows a master connected with two slaves through a switch. Master runs at 50ms cycle time and transmits payload through Process Data Object (PDO).
Figure – 1 Environment Set up
Cycle Time: 50 ms
Isochronous Data Size: 1 Byte Tx & 1 Byte Rx
Asynchronous Data Size: 1500 Bytes
The demo C program on the slave receives the data and loops it back into the network
The master is able to receive the data is sent into the network after the loop back at a delay of 200ms i.e. 4 cycles.
Figure – 2 Round trip time of a PDO
During the process master streams a video with the resolution of 176x144 @ 25fps into the network. One of the slaves in the network receives the streamed video with the delay of 2 seconds. The persistence (jitter) between the cycles was measured to be 4ms during the process.
Figure – 3 Jitter measurements
We see that the network is stable and deterministic at 50 ms
To further reduce the cycle time, we can port the ethernet driver into the linux kernel and try using RtPrempt