OBJECTIVE
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).
DEMO SETUP
Figure – 1 Environment Set up
PERFORMANCE NUMBERS
Configuration
- 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
Performance
- 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 176×144 @ 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
OBSERVATION
- 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 RtPreempt